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Biomedical subjects

I Lee

Publications and source records attributed to I Lee.

At least 19 recordsLinked to original sources
PubMed1996

Oxygenation in tumors by modified hemoglobins.

The effect of systemic injection of modified hemoglobin (Hb) prepared from bovine, human, or mouse Hb on tumor oxygenation was investigated. Hb was modified by (1) diisothiocyanatobenzenesulfonate (DIBS) to yield cross-linking within a tetramer; (2) glycolaldehyde (Glyal) to yield cross-linking between and within tetramers; (3) carboxymethylation (Cm) to change oxygen affinity; or (4) poly(ethylene glycol) (PEG) to yield attachment between tetramers. HGL9 (human glioma) in nude mice and FSaII (mice fibrosarcoma) in C3H mice were used as tumor models. Dose and time dependency were detected in the oxygenation effect by bovine-PEG-Hb. Internal cross-linkage prolonged the half-life in the circulation, and thus showed a significant effect. Compared to bovine-CmHb, bovine-DIBS-Hb and bovine-DIBS-CmHb were more effective. Decreasing the oxygen affinity by Cm significantly enhanced tumor oxygenation. Human-DIBS-CmHb was more effective than human-DIBS-Hb. These effects were caused by oxygen carrying capacity of modified Hbs as well as hemodynamic factors, and the injection seemed to reduce both perfusion-limited (acute) and diffusion-limited (chronic) hypoxia.

Animals↗
PubMed1995

A chemiluminescent immunoassay for the identification of functional single-chain antibodies.

Random mutagenesis of a template single-chain Fv (scFv) antibody generates a mutant library with members of varying ligand affinities; however, only a small population of these mutants exhibit strong (Kd approximately 1 nM) or improved affinities. We have therefore designed a chemiluminescent sandwich assay which can identify strong ligand-binding mutants expressed by Escherichia coli. A model system involving scFv 43C9 and selected mutants with varying hapten affinities was used to demonstrate the application of this methodology. Both the plaque and colony lifts of these scFvs were screened for hapten-binding activities with the chemiluminescent assay, and only strong binders were detected.

Antibodies, Bacterial↗
PubMed1995

Isolation and characterization of the chicken trypsinogen gene family.

Based on genomic Southern hybridizations and cDNA sequence analyses, the chicken trypsinogen gene family can be divided into two multi-member subfamilies, a six-member trypsinogen I subfamily which encodes the cationic trypsin isoenzymes and a three-member trypsinogen II subfamily which encodes the anionic trypsin isoenzymes. The chicken cDNA and genomic clones containing these two subfamilies were isolated and characterized by DNA sequence analysis. The results indicated that the chicken trypsinogen genes encoded a signal peptide of 15 to 16 amino acid residues, an activation peptide of 9 to 10 residues and a trypsin of 223 amino acid residues. The chicken trypsinogens contain all the common catalytic and structural features for trypsins, including the catalytic triad His, Asp and Ser and the six disulphide bonds. The trypsinogen I and II subfamilies share approximately 70% sequence identity at the nucleotide and amino acid level. The sequence comparison among chicken trypsinogen subfamily members and trypsin sequences from other species suggested that the chicken trypsinogen genes may have evolved in coincidental or concerted fashion.

Amino Acid Sequence↗
PubMed1995

Changing the inhibitory specificity and function of Cucurbita maxima trypsin inhibitor-V by site-directed mutagenesis.

Cucurbita maxima trypsin inhibitor-V (CMTI-V) is also a specific inhibitor of human blood coagulation factor beta-factor XIIa. A recombinant version of CMTI-V has allowed probing of roles of individual amino acid residues including the reactive site residue, lysine (P1), by site-directed mutagenesis. The K44R showed at least a 5-fold increase in inhibitory activity toward human beta-factor XIIa, while there was no change toward bovine trypsin. This result demonstrates that beta-factor-XIIa prefers an arginine residue over lysine residue, while trypsin is non-specific to lysine or arginine in its binding pocket. On the other hand, the specificity of CMTI-V could be changed from trypsin to chymotrypsin inhibition by mutation of the P1 residue to either leucine or methionine (K44L or K44M).

Animals↗
PubMed1995

Identification and characterization of a human cDNA homologous to yeast SKI2.

A monoclonal antibody, 170A1, which recognizes a nucleolar peptide of molecular weight 90,000, was raised. The protein was conserved among various vertebrates. To characterize the antigen, we screened a human fetal liver expression library using the monoclonal antibody as a probe. Molecular analyses of immunopositive clones suggested the presence of a novel cDNA. It appeared to be a single-copy gene and encoded about 4- and 5-kb mRNAs. The gene appeared to be expressed in every cell tested so far. Its deduced amino acid sequence revealed an overall homology to recently described yeast SKI2. The SKI2 gene of Saccharomyces cerevisiae encoded a nucleolar protein that is involved in the antiviral system. We report here the partial human cDNA sequence and the localization of the corresponding gene on chromosome 6p21.

Amino Acid Sequence↗
PubMed1995

Acute toxicity of the oil dispersant corexit 9554 to marine organisms.

The acute toxicity of a surfactant-based oil dispersant, Corexit 9554, to the early life stages of four marine species was identified using a closed, flow-through exposure system. Standardized, spiked exposures were used in order to impart a measure of reality to the data. The species were taxonomically diverse: a mollusc, the red abalone (Haliotis rufescens); a fish, the topsmelt (Atherinops affinis); a crustacean, the kelp forest mysid (Holmesimysis costata); and a macroalga, the giant kelp (Macrocystis pyrifera). Results indicated the Haliotis test to be most sensitive, followed by the Macrocystis test, and the Atherinops test, with the Holmesimysis test being least sensitive. Median-effect concentration estimates for the four species ranged from 8.0 to 184.3 initial ppm, a > 20-fold difference. Differences in sensitivity of the four tests were likely the result of both internal (morphological, physiological, etc.) and external (life stage, endpoint, etc.) factors.

Animals↗
PubMed1995

Lack of general correlation between interstitial fluid pressure and oxygen partial pressure in solid tumors.

Several studies have shown a decrease in blood perfusion and oxygen partial pressure (pO2), and an increase in interstitial fluid pressure (IFP) with increasing tumor size. However, it is not evident if the elevated IFP is a key parameter responsible for the poor perfusion and oxygenation of solid tumors. To this end, IFP and pO2 were measured in nine human tumor xenografts in immunodeficient mice at a fixed tumor size (approximately 250 mm3). IFP and pO2 were also measured as a function of tumor volume in one human colon adenocarcinoma (LS174T) and in one human glioblastoma (HGL-9). In LS174T tumors IFP did not vary with size (P < .07); however, median pO2 decreased from approximately 35 mm Hg in 100-mm3 tumors to approximately 15 mm Hg in tumors of approximately 500 mm3 (P < 0.001). In HGL-9 tumors an inverse correlation between IFP and pO2 was found; IFP increased (P < 0.001) and pO2 decreased (P < 0.001) with increasing tumor size. At a fixed tumor size of 250 mm3 no correlation was found between mean IFP and median pO2 (P < 0.5) or between the mean IFP and the hypoxic fraction (pO2 < 2.5 mm Hg) (P < 0.7) in the nine tumors studied. The absence of a general relationship between IFP and pO2 could result in part from differences in vascular resistance between tumors. For example, a high geometric resistance to blood flow on the arterial side will lead to a low IFP and blood flow, whereas an elevation of the venous resistance will reduce blood flow and increase IFP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Chemical platinization and its effect on excitation transfer dynamics and P700 photooxidation kinetics in isolated photosystem I.

Isolated photosystem I (PSI) reaction center/core antenna complexes (PSI-40) were platinized by reduction of [PtCl6]2- at 20 degrees C and neutral pH. PSI particles were visualized directly on a gold surface by scanning tunneling microscopy (STM) before and after platinization. STM results showed that PSI particles were monomeric and roughly ellipsoidal with major and minor axes of 6 and 5 nm, respectively. Platinization deposited approximately 1000 platinum atoms on each PSI particle and made the average size significantly larger (9 x 7 nm). In addition to direct STM visualization, the presence of metallic platinum on the PSI complexes was detected by its effect of actinic shading and electrostatic shielding on P700 photooxidation and P700+ reduction. The reaction centers (P700) in both platinized and nonplatinized PSI-40 were photooxidized by light and reduced by ascorbate repeatedly, although at somewhat slower rates in platinized PSI because of the presence of platinum. The effect of platinization on excitation transfer and trapping dynamics was examined by measuring picosecond fluorescence decay kinetics in PSI-40. The fluorescence decay kinetics in both platinized and control samples can be described as a sum of three exponential components. The dominant (amplitude 0.98) and photochemically limited excitation lifetime remained the same (16 ps) before and after platinization. The excitation transfer and trapping in platinized PSI-40 was essentially as efficient as that in the control (without platinization) PSI. The platinization also did not affect the intermediate-lifetime (400-600 ps) and long-lifetime (> 2500 ps) components, which likely are related to intrinsic electron transport and to functionally uncoupled chlorophylls, respectively. The amplitudes of these two components were exceptionally small in both of the samples. These results provide direct evidence that although platinization dramatically alters the photocatalytic properties of PSI, it does not alter the intrinsic excitation dynamics and initial electron transfer reactions in PSI.

Biophysical Phenomena↗
PubMed1995

Significance of magnetic resonance signal enhancement in evaluation of myocardial infarction in cats.

RATIONALE AND OBJECTIVES: To correlate magnetic resonance (MR) signal enhancement with pathophysiologic changes occurring during ischemia and reperfusion in evaluation of myocardial infarction in cats. METHODS: Seven cats were subjected to 150 minutes of occlusion of the left anterior descending coronary artery followed by 90 minutes of reperfusion. Gadolinium (Gd) diethylenetriaminepentaacetic acid-polylysine (molecular weight [mw] = 40 to 50 kd, DP230) contrast-enhanced MR images were acquired with coinjection of poly-L-lysine-fluorescein isothiocyanate (mW = 40 to 50 kd, DP219) as a fluorescent tracer molecule of the contrast agent. Signal intensities on the MR images and fluorescence activities on the resected cardiac specimens were measured. Pathologic examinations by electron and light microscopes and 2,3,5-triphenyltetrazolium chloride histochemical staining were performed on the specimens. RESULTS: Magnetic resonance signal intensity was lower in the center (3.49 +/- 0.36) than in the periphery (4.71 +/- 0.89) of the enhanced area. Fluorescence activities were absent in the normal myocardium; they were scant as nonspecific discrete dots in the center and numerous as specific interstitial distribution in the periphery of the ischemic myocardium. Electron and light microscopic examinations showed severely damaged ultrastructures of the center and moderately distorted ultrastructures of the periphery. CONCLUSIONS: The center of the MR signal-enhanced area is the infarct center with severe ultrastructural damages, which also might be an area of little or absent of blood reflow. Conversely, the peripheral-enhanced area is the infarct periphery with moderate myocardial damages.

Animals↗
PubMed1995

Presence of eosinophilic precursors in the human thymus: evidence for intra-thymic differentiation of cells in eosinophilic lineage.

The distribution of myeloid cells in the human thymus was investigated by light and electron microscopy, immunohistochemistry, and/or flow cytometry. A series of 74 thymic samples, from newborn to 37 year old patients, were studied. By light microscopy, aggregates of mononuclear cells were frequently present in intralobular septa and outer medulla. Among those cells, eosinophilic precursors (promyelocyte, myelocytes and metamyelocytes) were readily identified. These immature granular cells were present in all pre-involutional thymi, and were particularly frequent in the thymi of patients who were younger than 5 years of age. The cells made up 30-50% of the total eosinophilic population and were frequently observed as a group of cells at various stages of differentiation, suggesting that they differentiate from pre-existing precursors in the thymus. These eosinophilic precursors were mostly located in the intralobular septa and fibroreticular network at the corticomedullary junction, while mature eosinophils were scattered throughout the thymus. Flow cytometric analyses, using stem cell-enriched preparations, showed that cells expressing CD33 or CD34 constituted on average 2.55% and 3.33% (0.09% and 0.12% of the total cells), respectively. CD33+/CD34+ coexpressors were also identified, and they constituted 0.36% of the analyzed cells (0.01% of the total cells). No statistical difference in the proportions of CD33+ and/or 34+ cells was noted between any age groups. It is concluded that eosinophilic precursors present in the thymus differentiate into cells in the eosinophilic lineage in particular areas such as the intralobular septa and fibroreticular network of the outer medulla in preinvolutional human thymi.

Adolescent↗
PubMed1995

Adhered platelet morphology in diabetes mellitus.

We compared the morphology of platelets obtained from diabetic patients in various stages of retinopathy and nephropathy with those of control patients. The platelets were collected on to polyethylene films, processed and observed under scanning electron microscopy. Different platelet morphologies were observed within the diabetic group, correlating with the severity of complications, whereas platelets appeared normal in the control group. After more extensive follow-up and comparative studies, these preliminary observations could provide another diagnostic tool for detecting and evaluating severe complications associated with diabetes.

Case-Control Studies↗
PubMed1994

Enhancement of antigen-induced T-cell proliferation by soluble CD26/dipeptidyl peptidase IV.

The addition of a soluble recombinant CD26 (sCD26) enhanced proliferation of peripheral blood lymphocytes induced by the recall antigen tetanus toxoid. sCD26 itself did not provide a mitogenic signal and did not augment the proliferative response of T cells to other mitogenic stimuli such as phytohemagglutinin and anti-CD3. Dipeptidyl peptidase IV-negative sCD26 did not have this enhancement effect, implying a requirement for enzyme activity. It was found that there exists a large variation in the levels of human plasma sCD26/dipeptidyl peptidase IV in vivo which may regulate T-cell activity. Peripheral blood lymphocytes from individuals whose plasma sCD26 was high and responded strongly to tetanus toxoid stimulation were insensitive to the enhancing effects of exogenously added sCD26. This suggests that plasma sCD26 had modulated the responsiveness of T cells of these individuals in vivo and that the endogenous plasma sCD26 regulates immune responses by allowing antigen-specific T cells to exert a maximal response to their specific antigen.

Adjuvants, Immunologic↗
PubMed1994

Effect of hemodilution and resuscitation on tumor interstitial fluid pressure, blood flow, and oxygenation.

Hemodilution due to hemorrhage may increase tumor blood flow (TBF) by lowering blood viscosity and decrease tumor interstitial fluid pressure (TIFP) by moving fluid from the interstitium to the vascular compartment and by lowering microvascular pressure (MVP), mainly due to the decrease in systemic pressure. To test this hypothesis, we measured mean arterial blood pressure (MABP), TIFP, hematocrit, relative TBF (RBC flux), and intratumor pO2 during hemorrhage and volume restitution in severe combined immunodeficient mice, bearing LS174T human colon adenocarcinoma xenografts. MABP and TIFP significantly decreased after 0.2 ml of blood (approximately 12% of blood volume) was withdrawn. MABP decreased from 87.5 +/- 3.9 mmHg (mean +/- standard error) to 59.8 +/- 4.8 mmHg (n = 5, P = 0.01) within 2.5 min after the withdrawal of blood and then returned to control value within 10 min. TIFP gradually decreased from 18.7 +/- 2.3 mmHg to 11.3 +/- 0.9 mmHg after 1 hr (n = 8, P = 0.01), while RBC flux increased by a factor of 1.99 +/- 0.38 (n = 5, P = 0.02). The systemic hematocrit decreased from 51.2 to 45.9% (n = 7, P = 0.02). Tumor oxygenation did not significantly improve (median pO2 for control, 28 mmHg, and median pO2 after blood withdrawal, 32 mmHg; P = 0.14). When 0.2 ml blood was withdrawn and replaced (within 2.5 min) with the same volume of normal saline, MABP significantly decreased from 86.4 +/- 2.4 mmHg to 65.6 +/- 4.6 mmHg (n = 11) at 1 hr post-treatment (P = 0.001). TIFP decreased, but not significantly, from 24.2 +/- 2.9 mmHg to 20.4 +/- 2.4 mmHg (P = 0.35). Blood withdrawals in excess of 0.3 ml significantly decreased MABP and TIFP without recovery during 1 hr of observation. Volume restitution with hyperoncotic/hyperosmotic 6.0% Dextran 70 and 7.5% saline had effects attributable to a direct transmission of systemic pressure to the tumor microcirculation and to a lowering of tumor venous resistance. These effects appear to be common to saline blood restitution and volume top-load with Dextran 70. In conclusion, mild hemorrhage (withdrawal of approximately 12% of blood volume) can significantly lower TIFP without a reduction in TBF and pO2.

Adenocarcinoma↗
PubMed1994

Tissue-isolated human tumor xenografts in athymic nude mice.

An ex vivo perfused solid tumor preparation provides control over the physiological, biochemical, and pharmacological composition of the arterial input and easy access to the venous output. This is advantageous for studies of transport and metabolism in solid tumors. Here we present a tissue-isolated tumor preparation adapted to the nude mouse, allowing ex vivo perfusion of human tumor xenografts. Previously, such preparations have only been developed in rats, to study primarily rodent tumors. In the present study this new tumor preparation is physiologically characterized in comparison with subcutaneously transplanted tumors in nude mice using the human colon adenocarcinoma LS174T.

Adenocarcinoma↗
PubMed1994

Catalytic antibodies: perusing combinatorial libraries.

Combinatorial libraries are a promising alternative for isolating catalytic antibodies produced by the immune system in response to the transition-state analog of a given reaction. Large, diverse panels of antibodies with high affinity for the transition-state analog can be isolated using screening or selection approaches. Furthermore, we have estimated that nucleotide sequences that bear close similarity to the sequence for a known catalytic antibody occur in combination at frequencies sufficient for their detection in such libraries.

Amino Acid Sequence↗
PubMed1994

Changes in tumour blood flow, oxygenation and interstitial fluid pressure induced by pentoxifylline.

Pentoxifylline (PTX) has been shown to increase radiation damage to tumours and to decrease late radiation-induced injury to normal tissues. This tumour radiation sensitisation results from increased oxygen supply via improved tumour perfusion. We propose that the improved perfusion results from decreased viscous resistance and/or geometric resistance. The decreased flow resistance may be accompanied by a reduction in microvascular pressure (MVP). Since MVP is approximately equal to the interstitial fluid pressure (IFP), PTX should lead to a decrease in IFP. To test this hypothesis, we measured PO2, laser Doppler flow (RBC flux) and IFP in FSaII murine tumours at two doses (PTX at 25 and 100 mg per kg body weight) which sensitise this tumour to X-irradiation. We found that 25 mg kg-1 PTX was ineffective, but 100 mg kg-1 PTX was effective in increasing the PO2 of this tumour. PTX at 100 mg kg-1 (i.p.) increased median PO2 from 5 to 7 mmHg (P < 0.05) within 2 h, and decreased the fraction of PO2 values < 5 mmHg from 65% to 45% (P < 0.05). In support of our hypothesis, we found that with this dose of PTX, RBC flux in the tumour centre increased significantly (n = 6, P < 0.05) prior to an approximately 40% decrease (n = 13, P < 0.05) in tumour interstitial fluid pressure (TIFP), without changes in mean arterial blood pressure (MABP). In conclusion, a single i.p. administration of PTX at 100 mg kg-1 can increase oxygen availability in the tumour due to ameliorate hypoxia in tumour microregions. Second, PTX can lower the elevated TIFP without lowering the MABP.

Animals↗