Biomedical subjects

I Lee

Publications and source records attributed to I Lee.

At least 37 records · Page 2Linked to original sources

PubMed2001

Cytochrome C oxidase and the regulation of oxidative phosphorylation.

Life of higher organisms is essentially dependent on the efficient synthesis of ATP by oxidative phosphorylation in mitochondria. An important and as yet unsolved question of energy metabolism is how are the variable rates of ATP synthesis at maximal work load during exercise or mental work and at rest or during sleep regulated. This article reviews our present knowledge on the structure of bacterial and eukaryotic cytochrome c oxidases and correlates it with recent results on the regulatory functions of nuclear-coded subunits of the eukaryotic enzyme, which are absent from the bacterial enzyme. A new molecular hypothesis on the physiological regulation of oxidative phosphorylation is proposed, assuming a hormonally controlled dynamic equilibrium in vivo between two states of energy metabolism, a relaxed state with low ROS (reactive oxygen species) formation, and an excited state with elevated formation of ROS, which are known to accelerate aging and to cause degenerative diseases and cancer. The hypothesis is based on the allosteric ATP inhibition of cytochrome c oxidase at high intramitochondrial ATP/ADP ratios ("second mechanism of respiratory control"), which is switched on by cAMP-dependent phosphorylation and switched off by calcium-induced dephosphorylation of the enzyme.

Adenosine Triphosphate↗

PubMed2001

CD99 expression is positively regulated by Sp1 and is negatively regulated by Epstein-Barr virus latent membrane protein 1 through nuclear factor-kappaB.

Epstein-Barr virus (EBV)-encoded latent membrane protein-1 (LMP1) is highly expressed in Hodgkin and Reed-Sternberg (H-RS) cells from patients with EBV-associated Hodgkin disease. It was previously demonstrated that CD99 can be negatively regulated by LMP1 at the transcriptional level, and the decreased expression of CD99 in a B lymphocyte cell line generates H-RS-like cells. In this study, detailed dissection of the CD99 promoter region was performed to search regulatory factor(s) involved in the expression of the gene. Using various mutant constructs containing deletions in the promoter region, it was revealed that the maximal promoter activity was retained on 5'-deletion to the position -137 from the transcriptional initiation site. Despite the presence of multiple putative Sp1-binding sites in the promoter region, the site located at -95 contributes heavily as a positive cis-acting element to its basal promoter activity. However, on examination of the involvement of the positive-acting Sp1-binding site of the promoter for the repressive activity of LMP1, it appeared to be dispensable. Instead, the repressive effect was mapped to the nuclear factor (NF)-kappaB activation domains in the cytoplasmic carboxyl terminus of LMP1 despite the absence of the NF-kappaB consensus sequences in the CD99 promoter region. Furthermore, the decreased CD99 promoter activity by LMP1 was markedly restored when NF-kappaB activity was inhibited. Taken together, these data suggest that Sp1 activates, whereas LMP1 represses, transcription from the CD99 promoter through the NF-kappaB signaling pathway, and they might aid in the understanding of the molecular mechanisms of viral pathogenesis in EBV-positive Hodgkin disease. (Blood. 2001;97:3596-3604)

12E7 Antigen↗

PubMed2001

Substituted beta-cyclodextrins interact with PAMAM dendrimer-DNA complexes and modify transfection efficiency.

The efficiency of PAMAM dendrimer-mediated DNA transfer can be improved by the addition of substituted beta-cyclodextrins (beta-CDs) as formulation excipients. In vitro CAT expression increased approximately 200-fold when dendrimer/DNA/beta-CD formulations were applied on the surface of collagen membranes. The inclusion of beta-CD into the formulations resulted in particles that were smaller and more evenly distributed on the surface of the solid support. The average size of the complex formed at 50 microg/ml and at charge ratio of 1 decreased from 156 nm to 5.8 nm and 21.2 nm in 0.025-0.1% w/vol beta-CDs. Sulfonated beta-CDs bind to dendrimer and in the increased concentration may displace DNA in the dendrimer/DNA complex. High concentrations of amphoteric beta-CD do not dissociate dendrimer/DNA complexes; however, they may decrease their ability to transfect cells. At the optimized formulations the surface-modified beta-CDs may enhance solid support-based transfection in vitro, through modification of dendrimer/DNA complex composition and improved surface distribution.

Animals↗

PubMed2001

Adenosine triphosphate-dependent degradation of a fluorescent lambda N substrate mimic by Lon protease.

Escherichia coli Lon exhibits a varying degree of energy requirement toward hydrolysis of different substrates. Efficient degradation of protein substrates requires the binding and hydrolysis of ATP such that the intrinsic ATPase of Lon is enhanced during protein degradation. Degradation of synthetic tetrapeptides, by contrast, is achieved solely by ATP binding with concomitant inhibition of the ATPase activity. In this study, a synthetic peptide (FRETN 89-98), containing residues 89-98 of lambda N protein and a fluorescence donor (anthranilamide) and quencher (3-nitrotyrosine), has been examined for ATP-dependent degradation by E. coli and human Lon proteases. The cleavage profile of FRETN 89-98 by E. coli Lon resembles that of lambda N degradation. Both the peptide and protein substrates are specifically cleaved between Cys93 and Ser94 with concomitant stimulation of Lon's ATPase activity. Furthermore, the degradation of FRETN 89-98 is supported by ATP and AMPPNP but not ATPgammaS nor AMPPCP. FRETN 89-98 hydrolysis is eight times more efficient in the presence of 0.5 mM ATP compared to 0.5 mM AMPPNP at 86 microM peptide. The ATP-dependent hydrolysis of FRETN 89-98 displays sigmodial kinetics. The k(cat), [S](0.5), and the Hill coefficient of FRETN 89-98 degradation are 3.2 +/- 0.3 s(-1), 106 +/- 21 microM, and 1.6 respectively.

ATP-Dependent Proteases↗

PubMed2001

Nucleophilic substitution at the imidoyl carbon atom: intermediate mechanistic and reactivity behavior between carbonyl and vinyl carbon substitution.

Gas-phase nucleophilic substitution reactions at the imidoyl carbon have been investigated using chloride exchanges, Cl- + RY=CHCl right harpoon over left harpoon RY=CHCl + Cl- with Y = N and R = F, H or CH3, at the MP2, B3LYP and G2(+) levels using the MP2/6-311+G geometries. The results are compared with those for the vinyl (Y = CH) and carbonyl (Y = O) carbon substitution. The mechanism and reactivity of substitution at the imidoyl carbon are intermediate between those of carbonyl (SNpi) and vinyl carbon (SNsigma) substitution, which is directly related to the electronegativity of Y, CH < N < O. The prediction of competitive SNsigma with SNpi path for the imidoyl chloride is consistent with the S(N)1-like mechanism proposed for reactions in solution. The important factors in favor of an in-plane concerted SN2 (SNsigma) over an out-of-plane pi-attack (SNpi) path are (i) lower proximate sigma-sigma* charge-transfer energies (DeltaECT), (ii) stronger electrostatic stabilization (DeltaENCT), and (iii) larger lobe size on C(alpha) for the sigma*- than pi*-LUMO despite the higher sigma* than pi* level. The electron correlation energy effects at the MP2 level are overestimated for the relatively delocalized structure (S(N)pi TS) but are underestimated for the localized structure (SNsigma TS) so that the MP2 energies lead to a wrong prediction of preferred reaction path for the vinyl chloride. The DFT at the B3LYP level predicts correct reaction pathways but overestimates the electron correlation effects.

Journal Article↗

PubMed2001

Increased T cell autoreactivity in the absence of CD40-CD40 ligand interactions: a role of CD40 in regulatory T cell development.

Mutations in the CD40 ligand (CD40L) gene lead to X-linked immunodeficiency with hyper-IgM, which is often associated with autoimmune diseases. To determine the contribution of defective CD40-CD40L interactions to T cell autoreactivity, we reconstituted CD40-CD40L interactions by transferring T cells from CD40-deficient mice to syngenic athymic nude mice and assessed autoimmunity. T cells from CD40-deficient mice triggered autoimmune diseases accompanied with elevations of various autoantibodies, while those from wild-type mice did not. In CD40-deficient mice, the CD25(+) CD45RB(low) CD4(+) subpopulation which regulates T cell autoreactivity was markedly reduced. CD40-deficient APCs failed to induce T regulatory cells 1 producing high levels of an inhibitory cytokine, IL-10 in vitro. Furthermore, autoimmune development was inhibited when T cells from CD40-deficient mice were cotransferred with CD45RB(low) CD4(+) T cells from wild-type mice or with T regulatory cells 1 induced on CD40-expressing APCs. Collectively, our results indicate that CD40-CD40L interactions contribute to negative regulation of T cell autoreactivity and that defective interactions can lead to autoimmunity.

Animals↗

PubMed2001

Dissociating hippocampal subregions: double dissociation between dentate gyrus and CA1.

This study presents a double dissociation between the dentate gyrus (DG) and CA1. Rats with either DG or CA1 lesions were tested on tasks requiring either spatial or spatial temporal order pattern separation. To assess spatial pattern separation, rats were trained to displace an object which covered a baited food-well. The rats were then allowed to choose between two identical objects: one covered the same well as the sample phase object (correct choice), and a second object covered a different unbaited well (incorrect choice). Spatial separations of 15-105 cm were used to separate the correct object from the incorrect object. To assess spatial temporal order pattern separation, rats were allowed to visit each arm of a radial eight-arm maze once in a randomly determined sequence. The rats were then presented with two arms and were required to choose the arm which occurred earliest in the sequence. The choice arms varied according to temporal separation (0, 2, 4, or 6) or the number of arms that occurred between the two choice arms in the sample phase sequence. On each task, once a preoperative criterion was reached, each rat was given either a DG, CA1, or control lesion and then retested. The results demonstrated that DG lesions resulted in a deficit on the spatial task but not the temporal task. In contrast, CA1 lesions resulted in a deficit on the temporal task but not the spatial task. Results suggest that the DG supports spatial pattern separation, whereas CA1 supports temporal pattern separation.

Animals↗

PubMed2001

Intraoperative mild hypothermia does not increase the plasma concentration of stress hormones during neurosurgery.

PURPOSE: To determine how mild hypothermia (34 degrees C) affects the hemodynamic and the stress hormonal responses intraoperatively and during extubation in patients undergoing cerebral aneurysm surgery. METHODS: After induction, anesthesia was maintained with 1.2% isoflurane and 50% nitrous oxide. For the normothermia and the hypothermia groups, the body temperature was maintained at 36.9 +/- 0.3 degrees C and 34.2 +/- 0.2 degrees C respectively up to the recovery room. Hemodynamic changes were recorded continuously. Stress hormones comprising epinephrine, norepinephrine, ADH, ACTH, and cortisol were measured at the awake control, intraoperative, and extubation periods. RESULTS: Vital signs of the intraoperative and postextubation time periods were not significantly different between the normothermia and hypothermia groups except for a statistically lower pulse rate intraoperatively in the hypothermia group (P <0.05). In the control awake state, all five hormonal concentrations were similar between the two groups. Intraoperatively, all of the hormonal levels tended to be lower in the hypothermia group compared to the normothermia group, but only the epinephrine level decreased sufficiently to reach statistical significance (P <0.05). During extubation, all stress hormone concentrations, except norepinephrine, were lower in the hypothermia group (epinephrine: P <0.05; ADH: P <0.05; ACTH: P <0.05; cortisol: P <0.05). CONCLUSIONS: Our data suggest that intraoperative mild hypothermia neither significantly affects the blood pressure response nor increases the concentrations of stress hormones intraoperatively. Furthermore, mild hypothermia significantly decreased the plasma concentrations of stress hormones during the extubation period.

Adrenocorticotropic Hormone↗

PubMed2001

Characterization of the Japanese pufferfish (Takifugu rubripes) T-cell receptor alpha locus reveals a unique genomic organization.

Polymerase chain reactions with degenerate V gene segment primers were used to isolate the putative T-cell receptor alpha-chain gene (TCRA) from Japanese pufferfish (Takifugu rubripes). The putative TCRA chain cDNA is composed of an N-terminus leader peptide followed by the variable region and the constant region. The variable portion of the TCRA gene is encoded by V and J gene segments separated in the germline. As in mammals, the V-J junction sequences are GC rich and highly diversified. Amino acid residues that are required to maintain the function and structural integrity of the TCRA polypeptide, including the conserved Trp-Tyr-Lys and Tyr-Tyr-Cys motifs in the V gene segments, the Lys-Leu-X-Phe-Gly-X-Gly-Thr-X-Leu motif in the J gene segment, the three cysteine residues in the constant region and the charged residues in the transmembrane region are all preserved in the pufferfish. These conserved features suggest that the TCRA gene families in fish and mammals have evolved from a common ancestor.

Amino Acid Sequence↗

PubMed2001

Comparison the cognitive effect of anti-epileptic drugs in seizure-free children with epilepsy before and after drug withdrawal.

We studied the cognitive effects of antiepileptic drugs (AED), by investigating epileptic children who were seizure-free for at least 2 years and who had undergone fixed monotherapy. Seventy consecutive epileptic children (25 with carbamazepine (CBZ), 22 with phenobarbital (PB), and 23 with valproate (VPA)) were examined by Wechsler Intelligence Scale for Children-Revised (WISC-R) and auditory event-related potentials (P(300)) at three sessions: before AED reduction, then 1 and 7 months after complete withdrawal of treatment. There were no significant differences in IQ and subtests scores of WISC-R in any group at any of the three sessions. P(300) latencies were significantly increased in the children receiving PB but not in children receiving CBZ or VPA. P(300) amplitudes were increased but not significantly different among the three groups. These findings suggest that PB may affect cognitive function on children, but the changes of P(300) latencies may improve after discontinuation.

Anticonvulsants↗

PubMed2001

Comparative genomics of the human and mouse T cell receptor loci.

The availability of the complete genomic sequences of the human and mouse T cell receptor loci opens up new opportunities for understanding T cell receptors (TCRs) and their genes. The full complement of TCR gene segments is finally known and should prove a valuable resource for supporting functional studies. A rational nomenclature system has been implemented and is widely available through IMGT and other public databases. Systematic comparisons of the genomic sequences within each locus, between loci, and across species enable precise analyses of the various diversification mechanisms and some regulatory signals. The genomic landscape of the TCR loci provides fundamental insights into TCR evolution as highly localized and tightly regulated gene families.

Animals↗

PubMed2001

Palmitate decreases proton pumping of liver-type cytochrome c oxidase.

The H+/e- stoichiometry of reconstituted cytochrome c oxidase from bovine kidney, containing subunit VIaL (liver type), is 0.5 under standard conditions but 1.0 on addition of 1% cardiolipin to the lipid mixture (asolectin). Low concentrations of palmitate (half-maximal effect at 0.5 microm), but not laurate, myristate, stearate, oleate, 1-hexadecanol, palmitoyl glycerol and palmitoyl CoA, decreased the H+/e- ratio in the presence of cardiolipin from 1.0 to 0.5, accompanied by an increase of coupled, but not of uncoupled respiration of proteoliposomes. Cardiolipin and palmitate did not influence the H+/e- stoichiometry and respiration of reconstituted cytochrome c oxidase from bovine heart, containing subunit VIaH (heart-type). The H+/e- stoichiometry of the heart enzyme, however, is decreased from 1.0 to 0.5 by 5 mm intraliposomal ATP (instead of 5 mm ADP). It is assumed that palmitate binds to subunit VIaL. The partial uncoupling of proton pumping in cytochrome c oxidase is suggested to participate in mammalian thermogenesis.

Animals↗

PubMed2001

Lovastatin-induced E2F-1 modulation and its effect on prostate cancer cell death.

Lovastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, induces growth arrest in a variety of cancer cell lines. Its mechanism of action, however, has not been completely elucidated. E2F-1 is thought to act as an oncogene and a tumour suppressor, with its action probably dependent upon the cellular context. We have shown in this study that transcriptional regulation and proteasomal degradation of E2F-1 are critical regulatory events in lovastatin-induced cell death. Accompanying this is a reduction in the E2F-1-regulated expression of cell cycle genes such as c-myc, cyclin D1, cyclin A and cyclin B1. Cell cycle analysis demonstrated that the accumulation of apoptotic cells was preceded by a progressive decrease in the S-phase cell population in response to lovastatin. Although expression of E2F-1 was reduced in three prostate cancer cell lines-PC-3, LNCaP and DU-145-the p21 and p27 protein levels were not increased in all the cell lines treated, suggesting that increase in p21 and p27 protein expression per se is not responsible for lovastatin-mediated down-regulation of E2F-1. The subsequent apoptotic death of these cells in the presence of lovastatin can be prevented by forced ectopic expression of E2F-1. Taken together, these facts imply that E2F-1 is the target of an HMG-CoA inhibitor and critical cell death mediator in prostate cancer cells.

Apoptosis↗

PubMed2001

New control of mitochondrial membrane potential and ROS formation--a hypothesis.

A new control of mitochondrial membrane potential delta(psi)m and formation of reactive oxygen species (ROS) is presented, based on allosteric ATP-inhibition of cytochrome c oxidase at high intramitochondrial ATP/ADP ratios. Since the rate of ATP synthesis by the ATP synthase is already maximal at low membrane potentials (100-120 mV), the ATP/ADP ratio will also be maximal at this delta(psi)m (at constant rate of ATP consumption). Therefore the control of respiration by the ATP/ADP-ratio keeps delta(psi)m low. In contrast, the known 'respiratory control' leads to an inhibition of respiration only at high delta(psi)m values (150-200 mV) which cause ROS formation. ATP-inhibition of cytochrome c oxidase is switched on and off by reversible phosphorylation (via cAMP and calcium, respectively). We propose that 'stress hormones' which increase intracellular [Ca2+] also increase delta(psi)m and ROS formation, which promote degenerative diseases and accelerate aging.

Adenosine Triphosphate↗

PubMed2001

Anastomosis of vessels less than 2 mm with the vascular clip system clip applier.

Sutures may cause endothelial trauma and occlusion. The vascular clip system (VCS) clip applier may minimize endothelial injury. Fourteen carotid arteries of nine adult rabbits were transected and re-anastomosed with either #7-0 polypropylene (Group I, n=8) or VCS clips (Group II, n=6). The animals were sacrificed at 1, 3, 8, 14, and 30 days postoperatively. The operation time and bleeding amount were checked for each anastomosis. Carotid angiograms, photography, H&E staining and scanning electron microscopy (SEM) were performed. Fibrin and thrombus, inflammatory cell infiltration, endothelial disruption, luminal distortion, fibrosis, and wall thickening were compared. The luminal diameter was greater in group II. There were minimal differences in thrombosis, wall thickening and fibrosis between the two groups. However, fibrin, inflammatory cell infiltration, multinucleated giant cell formation, endothelial disruption, and luminal distortion were greater in group I. On SEM, group I showed trans-mural penetration. In contrast, group II showed suture margin eversion and no transmural penetration. Stenosis was greater in group I than in group II on carotid angiogram. The operation time was shorter in group II than in group I, i.e. 5+/-1.4 min vs. 11+/-3.8 min, respectively. The current data showed similar or superior results with VCS clips in comparison to conventional suturing with polypropylene.

Angiography↗

PubMed2001

Closed-loop identification and control application for dissolved oxygen concentration in a full-scale coke wastewater treatment plant.

The objective of this paper is to apply a closed-loop identification to actual dissolved oxygen control system in the coke wastewater treatment plant. It approximates the dissolved oxygen dynamics to a high order model using the integral transform method and reduces it to the first-order plus time delay (FOPTD) or second-order plus time delay (SOPTD) for the PID controller tuning. To experiment the process identification on the real plant, a simple set-point change of the speed of surface aerator under the closed-loop control without any mode change was used as an activation signal of the identification. The full-scale experimental results show a good identification performance and a good tracking ability for set-point change. As a result of improved control performance, the fluctuation of dissolved oxygen concentration variation has been decreased and the electric power saving has been accomplished.

Biomass↗

PubMed2001

Motexafin gadolinium: a redox active drug that enhances the efficacy of bleomycin and doxorubicin.

The effect of motexafin gadolinium (MGd), a redox mediator, on tumor response to doxorubicin (Dox) and bleomycin (Bleo) was investigated in vitro and in vivo. MES-SA human uterine sarcoma cells were studied in vitro using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide viability assay. Rif-1, a murine fibrosarcoma cell line, was studied using a clonogenic survival assay. Tumor growth delay assays were performed using the EMT-6 murine mammary sarcoma cell line in BALB/c mice. MGd (25-100 microM) produced dose-dependent enhancement of Bleo cytotoxicity to MES-SA cells. The IC(50) for Bleo was reduced by approximately 10-fold using 100 microM MGd. In clonogenic assays using Rif-1 cells, MGd enhanced the activity of Bleo approximately 1000-fold. This effect was shown to be mediated, in part, by MGd inhibition of potentially lethal damage repair. MGd enhanced the tumor response to bleomycin and Dox in vivo. MGd had no significant effect on the systemic exposure to Dox (expressed in terms of the plasma area under the curve, 0-24 h) and did not increase Dox myelosuppression. MGd enhanced the effectiveness of the redox active drugs, Bleo and Dox.

Animals↗

PubMed2000

Force measurements on platelet surfaces with high spatial resolution under physiological conditions.

Investigations on platelets are essential to understanding the regulation of hemostasis and thrombosis. Activated platelets undergo dramatic conformational and morphological changes mediated by numerous plasma proteins. AFM techniques can combine high spatial resolution with measurements of the mechanical properties of platelet surfaces. Here, we demonstrate two-dimensional force mapping over a human platelet adsorbed on glass under physiological buffer. The best resolution of platelet membrane elasticity we obtained was at 15.6x15.6 nm(2) pixel(-1). In addition, quantitative information on platelet surface charge density was extracted from individual force curves with the aid of DLVO theory.

Journal Article↗