Sang Kil Lee

Korea Research Institute of Standards and Science, Sŏul, Seoul, South Korea

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Publications (6)19.74 Total impact

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    ABSTRACT: We developed an ultra-low field (ULF)-nuclear magnetic resonance (NMR) measurement system capable of working with a measurement field (Bm) of several micro-tesla and performed basic NMR studies with a double relaxation oscillation superconducting quantum interference device (DROS) instead of conventional dc-SQUIDs. DROS is a SQUID sensor utilizing a relaxation oscillation between a dc-SQUID and a relaxation circuit; the new unit consists of an inductor and a resistor, and is connected in parallel with the SQUID. DROS has a 10 times larger flux-to-voltage transfer coefficient (∼mV/ϕ0) than that of the dc-SQUID, and this large transfer coefficient enables the acquisition of the SQUID signal with a simple flux-locked-loop (FLL) circuit using room temperature pre-amplifiers. The DROS second-order gradiometer showed average field noise of 9.2 μϕ0/√Hz in a magnetically shielded room (MSR). In addition, a current limiter formed of a Josephson junction array was put in a flux-transformer of DROS to prevent excessive currents that can be generated from the high pre-polarization field (Bp). Using this system, we measured an 1H NMR signal in water under 2.8 μT Bm field and reconstructed a one-dimensional MR image from the 1H NMR signal under a gradient field BG of 4.09 nT/mm. In addition, we confirmed that the ULF-NMR system can measure the NMR signal in the presence of metal without any distortion by measuring the NMR signal of a sample wrapped with metal. Lastly, we have measured the scalar J-coupling of trimethylphosphate and were able to confirm a clear doublet NMR signal with the coupling strength J3[P,H] = 10.4 ± 0.8 Hz. Finally, because the existing ULF-NMR/MRI studies were almost all performed with dc-SQUID based systems, we constructed a dc-SQUID-based ULF-NMR system in addition to the DROS based system and compared the characteristics of the two different systems by operating the two systems under identical experimental conditions.
    Journal of Applied Physics 09/2011; 110(5):053906. · 2.21 Impact Factor
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    ABSTRACT: Nitric oxide (NO) may aggravate neuronal damage after spinal cord injury (SCI). We hypothesized that NO produced by inducible nitric oxide synthase (iNOS) accelerates secondary damage to spinal tissue, which may be reversed by the neuroprotectant, melatonin. This study investigated the effects of combination therapy with melatonin (10 mg/kg) and exercise (10 m/min) on recovery from SCI caused by contusion. We examined locomotor recovery, iNOS gene expression, autophagic and apoptotic signaling, including Beclin-1, LC3, p53 and IKKalpha protein expression and histological alterations in the ventral horn of the spinal cord. Melatonin in combination with exercise resulted in significantly increased hindlimb movement (P < 0.05), a reduced level of iNOS mRNA (P < 0.05) and more motor neurons in the ventral horn, versus control SCI and SCI plus exercise alone, with no effect on the other signaling molecules examined. This study shows that combined therapy with melatonin and exercise reduces the degree of secondary damage associated with SCI in rats and supports the possible use of melatonin in combination with exercise to reduce the side effects related to exercise-induced fatigue and impairment.
    Journal of Pineal Research 03/2010; 48(3):270-81. · 7.30 Impact Factor
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    ABSTRACT: Olmesartan medoxomil (OLM) is an antihypertensive angiotensin II receptor blocker. OLM has a low bioavailability (BA), approximately 26% in humans, due to its low water solubility and efflux by drug resistance pumps in the gastrointestinal tract. Self-microemulsifying drug delivery system (SMEDDS), which is easily emulsified in aqueous media under gentle agitation and digestive motility, was formulated to increase the oral BA of OLM. Among the surfactants and oils studied, Capryol 90, Tween 20, and Tetraglycol were chosen and combined at a volume ratio of 1:6:3 on the basis of equilibrium solubility and phase diagram experiments. The mean droplet size of SMEDDS was 15 nm. In an oral absorption study in rats, SMEDDS formulation brought faster absorption compared to suspension, showing a T(max) value of 0.2 hr. The C(max) and AUC values of SMEDDS formulation were significantly higher than those of suspension, revealing a relative BA of about 170%. Our study demonstrated the potential usefulness of SMEDDS for the oral delivery of poorly absorbable compounds, including OLM.
    Archives of Pharmacal Research 11/2009; 32(11):1629-35. · 1.54 Impact Factor
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    ABSTRACT: Self-expanding metal stent has emerged as an effective treatment option for malignant gastroesophageal junction obstruction. However, data on the clinicopathologic factors associated with stent patency are still lacking. To investigate the long-term clinical outcomes and prognostic factors, including treatment modalities, affecting stent patency in patients with malignant gastroesophageal junction obstruction given self-expanding metal stent insertions. A total 89 patients who underwent self-expanding metal stent insertion for malignant gastroesophageal junction obstruction were enrolled. We analysed technical and clinical success rates, complications, and prognostic factors affecting stent patency. Self-expanding metal stent insertion was successful in all patients and clinical improvement was achieved in 93.3%. Stent malfunction occurred in 32.9% of patients. The median overall survival time and stent patency time were 143 (95% CI: 99-187) and 190 days (95% CI: 108-272), respectively. In multivariate analysis, radiation therapy after stent placement significantly prolonged stent patency (OR: 0.221; 95% CI: 0.055-0.884; p=0.033). A higher migration rate was observed in those patients given chemotherapy after covered self-expanding metal stent placement (no anticancer treatment: 10.0%, chemotherapy: 42.9%, chemoradiation therapy: 9.1%, p=0.042). Self-expanding metal stent is a feasible and effective treatment for malignant gastroesophageal junction obstruction. Radiation therapy after stent placement significantly prolongs overall stent patency and chemotherapy increases the migration rate of covered stents.
    Digestive and Liver Disease 09/2009; 42(6):436-40. · 3.16 Impact Factor
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    ABSTRACT: Genistein (GT) is an isoflavone from Leguminosae and has received much attention as a phytoestrogen. Genistin is a glycoside form of GT (genistein-7-O-beta-D-glucopyranoside, GT-glu) is mainly found in soy-derived foods. In this study, we examined the pharmacokinetic properties and bioavailability of GT in rats and compared with those of GT-glu. In order to characterize and compare the pharmacokinetics of GT and GT-glu, these compounds were administered intravenously and orally. The plasma concentration of GT was determined by HPLC after enzymatic hydrolysis. After oral administration of GT with various doses (4, 20, 40 mg/kg), the bioavailability of GT was 38.58, 24.34 and 30.75%, respectively. The T(max), C(max) and AUC(0-infinity) of GT after oral administration of GT (40 mg/kg), were 2h, 4876.19 ng/ml, 31,269.66 ng h/ml, respectively. When smaller amount of GT was administered, the faster T(max) was observed. Oral administration of GT-glu resulted in longer T(max), lower C(max), and greater bioavailability than that of GT. The pharmacokinetic parameters of GT following oral administration of GT-glu (64 mg/kg as GT-glu, 40 mg/kg as GT) were obtained as follows: 8h (T(max)), 3763.96 ng/ml (C(max)), 51,221.08 ng h/ml (AUC(0-infinity)) and 48.66% (absolute bioavailability), respectively. These results indicate that the oral bioavailability of GT-glu is greater than that of GT.
    International Journal of Pharmaceutics 07/2007; 337(1-2):148-54. · 3.99 Impact Factor
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    ABSTRACT: The impact of storage conditions on the permeability of porcine buccal mucosa to [3H]water and [14C]mannitol was assessed. The fresh porcine buccal tissue (fresh tissue) was obtained by utilizing pig heads within 24 hours of slaughter. The stored and frozen porcine buccal tissues (stored tissue and frozen tissue) were obtained after the storage of the tissue intact in the pig heads at 4 degrees C or -20 degrees C, respectively, for 24 h. The results demonstrated that the barrier properties of the porcine buccal mucosa were maintained with regard to [3H]water permeability when stored at 4 degrees C for 24 h. However, freezing the tissue resulted in tissue damage illustrated by a significant increase in [3H]water permeability. [14C]Mannitol does not appear to be a suitable model solute to assess the ex vivo permeability of porcine buccal mucosa due to its extremely low permeability.
    Archives of Pharmacal Research 09/2002; 25(4):546-9. · 1.54 Impact Factor

Publication Stats

61 Citations
19.74 Total Impact Points

Institutions

  • 2011
    • Korea Research Institute of Standards and Science
      • Brain and Cognition Measurement Center
      Sŏul, Seoul, South Korea
  • 2009
    • Inje University
      • Department of Pharmaceutical Engineering
      Kŭmhae, South Gyeongsang, South Korea