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Biomedical subjects

Jai H Lee

Publications and source records attributed to Jai H Lee.

7 recordsLinked to original sources
PubMed2005

Oxidation mechanism of As(III) in the UV/TiO2 system: evidence for a direct hole oxidation mechanism.

Although it is well-known that As(III) is oxidized to As(V) in the UV/TiO2 system, the main oxidant for that reaction is still not clear. Accordingly, the present study aims at reinvestigating the TiO2-photocatalyzed oxidation mechanism of As(III). We performed a series of As(II) oxidation experiments by using UV-C/H2O2 and UV-A/TiO2, focusing on the effects of competing compounds. The experiment with UV-C/H2O2 indicated that HO2*/O2-* is not an effective oxidant of As(III) in the homogeneous phase. The effects of oxalate, formate, and Cu(II) on the photocatalytic oxidation of As(III) contradicted the controversial hypothesis that HO2*/ O2-* is the main oxidant of As(III) in the UV/TiO2 system. The effect of As(III) on the TiO2-photocatalyzed oxidations of benzoate, terephthalate, and formate was also incompatible with the superoxide-based As(II) oxidation mechanism. Instead, the experimental observations implied that OH* and/or the positive hole are largely responsible forthe oxidation of As(III) in the UV/TiO2 system. To determine which species plays a more significant role, the effects of methanol and iodide were tested. Since excess methanol did not retard the oxidation rate of As(III), OH* seems not to be the main oxidant. Therefore, the best rationale regarding the oxidation mechanism of As(III) in the UV/TiO2 system seems to be the direct electron transfer between As(III) and positive holes. Only with this mechanism, it was possible to explain the data of this study. Besides the mechanistic aspect, an application method for this technology was sought. The usage of UV/TiO2 for oxidizing As(II) requires a posttreatment in which both As(V) and TiO2 should be removed from water. For this objective, we applied FeCl3 and AIK(SO4)2 as coagulants, and the result implied that the combined usage of TiO2 and coagulation might be a feasible solution to treat arsenic contamination around the world.

Adsorption↗
PubMed2005

Interleukin 12 and interferon-gamma synthetic deficiency is associated with dendritic cell cytopenia after cardiac surgery.

Traumatic or inflammatory injury associates with deactivation of monocytes and impaired synthesis of proinflammatory cytokines. We conducted a prospective, observational study to test whether cardiac surgery additionally impaired dendritic and natural killer (NK) cell functions responsible for innate immune production of interleukin (IL)-12-dependent interferon (IFN)-gamma in response to bacteria or toll-like receptor agonists. Blood samples were taken just before induction of anesthesia and 24 h postoperatively. LPS- and fixed Staphylococcus aureus-inducible IFNgamma synthesis in whole blood culture after surgery was reduced to 5% of preoperative values (P < 0.001). Production of IL-12 p70, a critical inducer of IFNgamma in the innate immune response, was reduced to 30% of that produced by preoperative samples (P = 0.013). Circulating CD11c, DR myeloid dendritic cells (DC) that are known sources of IL-12 p70 in normal blood, declined to approximately 25% of presurgical numbers (P = 0.004). Experimental depletion of CD11c, but not CD14, cells from normal peripheral blood mononuclear cell (PBMC) similarly disabled Staphylococcus aureus Cowan 1 (SAC)-induced production of IL-12 p70 and IFNgamma. Consistent with SAC-induced IFNgamma expression in CD56 NK and NK-T cells, CD56 depletion ablated IFNgamma production in normal whole blood. However, repletion of IL-12 p70, IL-18, IL-15, and IL-23 in postoperative blood failed to restore presurgical levels of IFNgamma synthesis (P < 0.05). We conclude that DC cytopenia after major surgery is sufficient to explain postoperative IL-12 p70 and IFNgamma synthetic deficiency. In addition, postoperative blood became hyporesponsive to IFNgamma-inducing cytokines as a further contribution to IFNgamma insufficiency. The novel finding of DC cytopenia after major surgery may portend a lack of other immunologic functions provided by this potent accessory cell population.

Dendritic Cells↗
PubMed2004

A kinetic method for HO2*/O2*- determination in advanced oxidation processes.

A new kinetic method is developed for the determination of hydroperoxyl radical (HO(2)(*))/superoxide radical (O(2)(*)(-)) in aqueous solution, and the calibration using a kinetic half-life technique is also established for determining the concentration of HO(2)(*)/O(2)(*)(-) as produced in the UV/H(2)O(2) process. This new method is based on the reduction of Fe(3+)-EDTA into Fe(2+)-EDTA by HO(2)(*)/O(2)(*)(-) and the well-known Fenton-like reaction of H(2)O(2) and Fe(2+)-EDTA to yield the hydroxyl radicals (OH(*)). Benzoic acid scavenges the OH radicals to produce hydroxybenzoic acids, which are analyzed by fluorescence detection (lambda(ex) = 320 nm; lambda(em) = 400 nm). The limit of detection for the new method depends on the pH values, and it is determined as 3.22 x 10(-)(11) M with signal-to-noise ratio of 2 at pH 5. In addition, the present technique has the advantage of using inexpensive and easily available nonenzymatic reagents that do not require the specific instrument and chemicals and of being insensitive to the moderate concentration of possible interferences often found in aqueous phase.

Journal Article↗
PubMed2002

Sonolytic degradation of methyl tert-butyl ether: the role of coupled Fenton process and persulphate ion.

The sonolytic degradation of methyl tert-butyl ether (MTBE) has been investigated at ultrasonic frequency of 20 kHz. The observed pseudo-first-order rate constant decreased from 1.25 x 10(-4) to 5.32 x 10(-5) s(-1) as the concentration of MTBE increased from 2.84 x 10(-2) to 2.84 x 10(-1) mM. The rate of degradation of MTBE increased with the increase of the power density of ultrasonicator and also with the rise in reactor system temperature. In the presence of oxidising agent, potassium persulphate, the sonolytic rate of degradation of MTBE was accelerated substantially. Tert-butyl formate (TBF) and acetone were found to be the major intermediates of the degradation of MTBE. It is found that the ultrasound/Fe2+/H2O2 method is promising process for the degradation of MTBE. More than 95% degradation of MTBE (2.84 x 10(-2) mM) along with its intermediate products has been achieved during the coupled ultrasound/Fe2+/ H2O2 method. Hence, the coupled ultrasound/Fe2+/H2O2 may be a viable method for the degradation MTBE within a short period of time than the ultrasound irradiation process only. A kinetic model, based on the initial rates of degradation of MTBE and TBF, provides a good agreement with the experimental results.

Carcinogens↗
PubMed2002

Identification and characterization of atrioventricular parasympathetic innervation in humans.

INTRODUCTION: We hypothesized that in humans there is an epicardial fat pad from which parasympathetic ganglia supply the AV node. We also hypothesized that the parasympathetic nerves innervating the AV node also innervate the right atrium, and the greatest density of innervation is near the AV nodal fat pad. METHODS AND RESULTS: An epicardial fat pad near the junction of the left atrium and right inferior pulmonary vein was identified during cardiac surgery in seven patients. A ring electrode was used to stimulate this fat pad intraoperatively during sinus rhythm to produce transient complete heart block. Subsequently, temporary epicardial wire electrodes were sutured in pairs on this epicardial fat pad, the high right atrium, and the right ventricle by direct visualization during coronary artery bypass surgery in seven patients. Experiments were performed in the electrophysiology laboratory 1 to 5 days after surgery. Programmed atrial stimulation was performed via an endocardial electrode catheter advanced to the right atrium. The catheter tip electrode was moved in 1-cm concentric zones around the epicardial wires by fluoroscopic guidance. Atrial refractoriness at each catheter site was determined in the presence and absence of parasympathetic nerve stimulation (via the epicardial wires). In all seven patients, an AV nodal fat pad was identified. Fat pad stimulation during and after surgery caused complete heart block but no change in sinus rate. Fat pad stimulation decreased the right atrial effective refractory period at 1 cm (280 +/- 42 msec to 242 +/- 39 msec) and 2 cm (235 +/- 21 msec to 201 +/- 11 msec) from the fat pad (P = 0.04, compared with baseline). No significant change in atrial refractoriness occurred at distances >2 cm. The response to stimulation decreased as the distance from the fat pad increased. CONCLUSION: For the first time in humans, an epicardial fat pad was identified from which parasympathetic nerve fibers selectively innervate the AV node but not the sinoatrial node. Nerves in this fat pad also innervate the surrounding right atrium.

Adipose Tissue↗
PubMed2002

Earlier recovery with beating-heart surgery: a comparison of 300 patients undergoing conventional versus off-pump coronary artery bypass graft surgery.

OBJECTIVE: To compare outcomes and cost of off-pump coronary artery bypass (OP-CAB) surgery versus cardiopulmonary bypass-assisted coronary artery bypass graft (CABG) surgery. DESIGN: Retrospective review. SETTING: A tertiary care university teaching hospital. PARTICIPANTS: Patients (n = 300) undergoing isolated CABG surgery performed by a single surgeon between July 1998 and February 2000. INTERVENTIONS: Two groups of patients were compared: 150 consecutive patients undergoing OP-CAB surgery and a matched cohort of 150 consecutive patients undergoing conventional CABG surgery. MEASUREMENTS AND MAIN RESULTS: The 2 groups were evenly matched in terms of age and incidence of diabetes, hypertension, peripheral vascular disease, left main disease, prior strokes, congestive heart failure, and recent infarctions. OP-CAB procedures required 3.3 grafts per patient versus 3.8 grafts per patient required for CABG surgery (p = 0.02). Overall mortality was 2.0% (1.3% in the OP-CAB surgery group v 2.7 % in the CABG surgery group; p = NS). Extubation times (6.6 hours v 9.5 hours; p = 0.003), surgical intensive care unit length of stay (39 hours v 49 hours; p = 0.03), and hospital length of stay (6.1 days v 7.0 days; p = 0.04) were all significantly shorter for the OP-CAB surgery group. The combined aggregate endpoints of death and major morbidity were significantly less in the OP-CAB surgery group (5.3% v 12.7%; p = 0.02). CONCLUSION: OP-CAB surgery is associated with low morbidity and mortality and accelerated recovery compared with conventional CABG surgery. OP-CAB surgery may represent the ideal revascularization strategy for patients at high risk for undergoing cardiopulmonary bypass.

Adult↗
PubMed2002

Hemoptysis as an unusual presenting symptom of invasion of a descending thoracic aortic aneurysmal dissection by lung cancer.

A 70-year-old woman with a known chronic dissecting aneurysm of the descending thoracic aorta presented with new-onset back pain and hemoptysis. The hemoptysis was thought to be the result of invasion of the bronchial tree by the aneurysm. During surgical repair, a lesion that appeared to be a pulmonary abscess was discovered to be adhering to the aortic tissue, and the patient underwent a localized pulmonary resection. The pathology report of the surgical specimens revealed squamous cell carcinoma of the lung with infiltration of the aortic wall. The patient died of lung cancer 6 months later. Hemoptysis was an unusual presentation in a case of lung cancer that had invaded a stable chronic aortic aneurysm.

Aged↗