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Biomedical subjects

K Choi

Publications and source records attributed to K Choi.

At least 19 recordsLinked to original sources
PubMed2001

Endogenous glycosylphosphatidylinositol-specific phospholipase C releases renal dipeptidase from kidney proximal tubules in vitro.

Spontaneous enzymic release of renal dipeptidase (RDPase; EC 3.4.13.19), a glycosylphosphatidylinositol (GPI)-linked ectoenzyme, was observed in vitro during incubation of porcine proximal tubules at 37 degrees C. Triton X-114 phase separation of the released RDPase showed that the majority of the enzyme activity partitioned into the aqueous phase, indicating its hydrophilic nature. Immunoblot analyses using an antibody against the cross-reacting determinant (CRD) inositol 1,2-cyclic monophosphate, the epitope formed by phospholipase C (PLC) cleavage of the GPI anchor on a protein, detected the released RDPase. Reprobing the immunoblot with an anti-RDPase serum showed the RDPase band co-migrating with the CRD band. The release of RDPase from the proximal tubules was a Ca(2+)-dependent process and had a pH optimum of 9.0. These results indicate that RDPase is released from the proximal tubules by the action of a distinct endogenous GPI-specific PLC.

Animals↗
PubMed2000

Target site search and effective inhibition of leukaemic cell growth by a covalently closed multiple anti-sense oligonucleotide to c-myb.

Systematic secondary structure simulation of a target mRNA sequence is shown to be effective for locating a good anti-sense target site. Multiple selected anti-sense sequences were placed in a single molecule. The anti-sense oligonucleotide (oligo) was covalently closed to avoid exonuclease activities and was designated CMAS (covalently closed multiple anti-sense)-oligo. CMAS-oligo was found to be stable, largely preserving its structural integrity after 24 h of incubation in the presence of either exonuclease III or serum. When human c-myb mRNA was targeted by the c-myb CMAS-oligo, expression of the gene was completely abolished. Further, tumour cell growth was inhibited by 82+/-3% as determined by an MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay and by 90+/-1% by [(3)H]thymidine incorporation. When a leukaemic cell line K562 was treated with CMAS-oligo, colony formation on soft agarose was also decreased by 93%. In contrast, treatment with a scrambled control oligo did not significantly inhibit leukaemic cell growth. These results suggest that a rational target site search is possible for an anti-sense oligo and that CMAS-oligo can be employed as an effective anti-sense agent with enhanced stability.

Cell Division↗
PubMed2000

Potent growth inhibition of leukemic cells by novel ribbon-type antisense oligonucleotides to c-myb1.

We studied the effects of antisense oligonucleotides (AS oligos) with a novel structure. The AS oligos were covalently closed to avoid exonuclease activities by enzymatic ligation of two identical molecules. The AS oligos of a ribbon type (RiAS oligos) consist of two loops containing multiple antisense sequences and a stem connecting the two loops. Three antisense sequences targeting different binding sites were placed in a loop that was designed to form a minimal secondary structure by itself. RiAS oligos were found to be stable because they largely preserved their structural integrity after 24 h incubation in the presence of either exonuclease III or serums. When a human promyelocytic cell line, HL-60, was treated with RiAS oligos to c-myb, c-myb expression was effectively ablated. Cell growth was inhibited by >90% determined by both the 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyltetrazolium bromide assay and [(3)H]thymidine incorporation. Further, when the leukemic cell line K562 was treated with c-myb RiAS oligos, colony formation on soft agarose was reduced by 92 +/- 2%. These results suggest that RiAS oligos may be employed for developing molecular antisense drugs as well as for the functional study of a gene.

Base Sequence↗
PubMed2000

Acute and chronic life cycle toxicity of acenaphthene and 2,4,6-trichlorophenol to the midge Paratanytarsus parthenogeneticus (Diptera: Chironomidae).

The acute and life cycle toxicities of acenaphthene and 2,4,6-trichlorophenol (2,4,6-TCP) were evaluated using the parthenogenic dipteran larva, Paratanytarsus parthenogeneticus, of the family Chironomidae. Static 48 h acute toxicity tests employed third instar larvae, and the flow-through 20-day life cycle tests were initiated with eggs. No acute lethal effect was observed in the saturated concentration (2.1 mg/l) of acenaphthene in water, and the median lethal concentration of 2,4,6-TCP was approximately 40 mg/l. In the life cycle toxicity test with acenaphthene, hatchability of the midge was affected by 50% at an exposure concentration of approximately 0.17 mg/l. The median effective concentration for larval, pupal and adult development was found between 0.06 and 0.07 mg/l, respectively, and these were significantly lower than the effective concentration for hatching success. With regard to 2,4,6-TCP toxicity, the median effective concentration for midge hatchability was 4.23 mg/l. The larval development, pupal formation and adult emergence, however were impeded at 1.60, 1.46 and 1.33 mg/l, respectively. Each level was noticeably lower than the median effective concentration for hatchability. The concentrations for each compound that interfered with the development to fourth instar, pupa and adult were not significantly different. These results indicate that larval developments after hatching were the most sensitive stages and affected the success of midge growth.

Acenaphthenes↗
PubMed2000

Calreticulin couples calcium release and calcium influx in integrin-mediated calcium signaling.

The engagement of integrin alpha7 in E63 skeletal muscle cells by laminin or anti-alpha7 antibodies triggered transient elevations in the intracellular free Ca(2+) concentration that resulted from both inositol triphosphate-evoked Ca(2+) release from intracellular stores and extracellular Ca(2+) influx through voltage-gated, L-type Ca(2+) channels. The extracellular domain of integrin alpha7 was found to associate with both ectocalreticulin and dihydropyridine receptor on the cell surface. Calreticulin appears to also associate with cytoplasmic domain of integrin alpha7 in a manner highly dependent on the cytosolic Ca(2+) concentration. It appeared that intracellular Ca(2+) release was a prerequisite for Ca(2+) influx and that calreticulin associated with the integrin cytoplasmic domain mediated the coupling of between the Ca(2+) release and Ca(2+) influx. These findings suggest that calreticulin serves as a cytosolic activator of integrin and a signal transducer between integrins and Ca(2+) channels on the cell surface.

Animals↗
PubMed2000

Grass carp (Ctenopharyngodon idellus) bile may inhibit the release of renal dipeptidase from the proximal tubules by nitric oxide generation.

There are many reports on acute renal failure (ARF) after ingestion of grass carp bile (CB; Ctenopharyngodon idellus). Renal dipeptidase (RDPase; EC 3.4.13.19) is a glycosylphosphatidylinositol-anchored ectoenzyme within the renal proximal tubules (PTs) and is proposed as a diagnostic enzyme of renal disease. We examined the release of RDPase following treatment with CB and various nitric oxide (NO) related compounds in porcine PTs. The RDPase release from PTs was inhibited by CB in a concentration-dependent manner and was also inhibited by sodium nitroprusside (direct NO donor) and L-arginine (NO synthase substrate) in the tested range (0-12 mM). CB-treated (0. 1 mg/ml) PTs showed a decreased RDPase activity in comparison with the control group. This inhibition was blocked by 2 mM L-NAME (NO synthase inhibitor) and U73122 (inhibitor of phosphatidylinositol-specific phospholipase C) in a concentration-dependent manner. Eel bile (0-0.1 mg/ml), used as the control, did not significantly affect the RDPase release from PTs. The NO concentration was observed as nitrite, the degradation product of the NO metabolism, increased in proportion to CB and L-arginine. The increase of nitrite to 151.5% by CB treatment (0.1 mg/ml) was blocked by 2 mM L-NAME (95.5%). When the phospholipase C pathway was blocked by 10 and 20 microM U73122, the nitrite generation decreased to 122.7 and 89.4%, respectively. These results strongly suggest that NO generation and the phospholipase C pathway affect the RDPase release from the PTs and that they may be involved in the development of ARF in vivo following CB ingestion. The release of RDPase from PTs could be a useful tool not only for this CB-caused ARF, but also for the elucidation of other biochemical mechanisms.

Animals↗
PubMed2000

Basic fibroblast growth factor positively regulates hematopoietic development.

Recently identified BLast Colony Forming Cells (BL-CFCs) from in vitro differentiated embryonic stem (ES) cells represent the common progenitor of hematopoietic and endothelial cells, the hemangioblast. Access to this initial cell population committed to the hematopoietic lineage provides a unique opportunity to characterize hematopoietic commitment events. Here, we show that BL-CFC expresses the receptor tyrosine kinase, Flk1, and thus we took advantage of the BL-CFC assay, as well as fluorescent activated cell sorter (FACS) analysis for Flk1(+) cells to determine quantitatively if mesoderm-inducing factors promote hematopoietic lineage development. Moreover, we have analyzed ES lines carrying targeted mutations for fibroblast growth factor receptor-1 (fgfr1), a receptor for basic fibroblast growth factor (bFGF), as well as scl, a transcription factor, for their potential to generate BL-CFCs and Flk1(+) cells, to further define events leading to hemangioblast development. Our data suggest that bFGF-mediated signaling is critical for the proliferation of the hemangioblast and that cells expressing both Flk1 and SCL may represent the hemangioblast.

Activins↗
PubMed1999

Complications of buttress plate stabilization of cervical corpectomy.

STUDY DESIGN: A retrospective analysis of 14 patients treated with cervical corpectomy and buttress plate fixation. OBJECTIVES: To determine the complications of buttress plate fixation following multilevel cervical corpectomies. SUMMARY OF BACKGROUND DATA: Buttress plate fixation of multilevel cervical corpectomy has recently been reported. Biomechanical data suggests that it is preferable to long plates spanning the entire corpectomy site. There are no clinical studies that have specifically addressed the complications of this type of plate fixation. METHODS: The records and radiographs of all patients who had undergone cervical buttress plate fixation following anterior cervical corpectomy for myelopathy were independently reviewed. Twelve of the patients had three-level corpectomies and two had two-level corpectomies. All patients had placement of a short plate at the inferior end of the construct with sufficient overhang to act as a buttress against graft extrusion. Three patients underwent posterior cervical fusion in addition to the anterior procedure. RESULTS: Graft extrusion. One patient had complete graft extrusion on the third post-operative night. A second patient who had undergone circumferential fusion had minimal plate dislodgement secondary to graft settling. Pseudarthrosis. Three patients had pseudarthroses. Two of these required revision posterior surgery. Neurologic. None of the patients suffered neurologic complications. With the exception of the one patient who died, the rest of the patients all improved by at least one Nurick grade. CONCLUSION: The most catastrophic complication in the present series was plate dislodgement causing airway compromise and eventually resulting in death. Surgeons who utilize these types of buttress plates without additional posterior instrumentation should be aware of the potential complications of buttress plate fixation.

Adult↗
PubMed1999

Combinatorial Methods for the Synthesis of Aluminophosphate Molecular Sieves.

Automatic dispensing of reagents into autoclave blocks followed by synthesis, isolation, and automated structure analysis with X-ray diffractometry represents an efficient methodology for the combinatorial synthesis of microporous materials. The figure shows a typical diffractogram of as-synthesized AFI-type molecular sieves taken with a CCD camera.

Journal Article↗
PubMed1999

In vitro hematopoietic and endothelial potential of flk-1(-/-) embryonic stem cells and embryos.

Mice deficient in the Flk-1 receptor tyrosine kinase are known to die in utero because of defective vascular and hematopoietic development. Here, we show that flk-1(-/-) embryonic stem cells are nevertheless able to differentiate into hematopoietic and endothelial cells in vitro, although they give rise to a greatly reduced number of blast colonies, a measure of hemangioblast potential. Furthermore, normal numbers of hematopoietic progenitors are found in 7.5-day postcoitum flk-1(-/-) embryos, even though 8. 5-day postcoitum flk-1(-/-) embryos are known to be deficient in such cells. Our results suggest that hematopoietic/endothelial progenitors arise independently of Flk-1, but that their subsequent migration and expansion require a Flk-1-mediated signal.

Animals↗
PubMed1999

Release of renal dipeptidase from rabbit renal proximal tubules and its inhibition by gentamicin.

Effects of several drugs on rabbit renal proximal tubules were examined for the applicability of renal dipeptidase (RDPase, EC 3. 4. 13. 11) release as a model system to study nephrotoxicity. The proximal tubule prepared by the method of Taub (1990) released RDPase spontaneously in the control experiment which was confirmed by Western blotting. RDPase was also released from cisplatin, lipopolysaccharide (LPS), and indomethacin-treated tubules. Gentamicin inhibited RDPase release in a concentration-dependent manner. This RDPase release system may not be a general model to screen nephrotoxicity but could be a useful source of RDPase purification in a simple and inexpensive way.

Animals↗
PubMed1999

Optimal operating parameters in the composting of swine manure with wastepaper.

A series of experiments were conducted to determine the optimal conditions for composting of swine manure and wastepaper. The aeration rate and mixing ratio were the variables investigated. In the first study (Study-1), four experiments each with the same mixing ratio but a different aeration rate were carried out. In the second study (Study-2), different mixing ratios were investigated, each however with the same aeration rate which was found to be optimal from Study-1. Composting efficiencies were evaluated on the temperature profile and the reduction of C/N ratio. From the aeration rates of 200, 500, 1000, and 1500 mL/min.kg_vs that were evaluated, the aeration rate of 500 mL/min.kg_vs and higher showed good results. In Study-2, where the initial C/N ratios were 20, 25, 30, and 35 respectively, the C/N ratio of 30 was found to be optimal. In conclusion, the composting of swine manure with the amendment of wastepaper was best carried out at the aeration of > 500 mL/min.kg_vs and C/N ratio of 30.

Air↗
PubMed1999

Acute bereavement care in the emergency department: does the professional-supported volunteers model work?

The aims of our study were to study the early impact of bereavement and to evaluate the effectiveness of the bereavement care given by our multidisciplinary team to close relatives of a sudden death, measured by the intensity of grief reaction (Texas Revised Inventory of Grief). The study sample consisted of close relatives of patients certified dead at the accident and emergency department (AED) between March 1996 and February 1997. The relatives received immediate care at the AED and were supported continually by the members of the bereavement care team. The control sample (without acute bereavement care) consisted of close relatives contacted by the liaison nursing officer in the previous year. The intensity of grief reactions were assessed by the volunteer grief counsellors at 6 months. The mean score of the intensity of grief reactions were 41.8 and 34.6 in the control (n = 11) and study (n = 18) groups respectively among high risk sample (p = 0.04). However, in the low risk sample, the mean scores were 35.3 and 30.2 in the control (n = 18) and study (n = 25) groups respectively (p = 0.11). Our study suggests that the bereavement care was especially effective in reducing the intensity of the grief at 6 months in the high risk group.

Adolescent↗
PubMed1998

Generation of a primitive erythroid cell line and promotion of its growth by basic fibroblast growth factor.

An immortalized cell line representing the primitive erythroid (EryP) lineage was established from in vitro-differentiated progeny (embryoid bodies [EBs]) of embryonic stem (ES) cells using a retroviral insertional mutation, and has been termed EB-PE for embryoid body-derived primitive erythroid. Even though EB-PE cells are immortalized, they show characteristics of normal EryP cells, such as gene expression and growth factor dependency. In addition, EB-PE cells can differentiate further in culture. Investigation of growth factor requirements of EB-PE cells showed that basic fibroblast growth factor (bFGF) and erythropoietin (Epo) play unique roles in EB-PE proliferation and differentiation. While bFGF was a strong mitogen, Epo was required for both proliferation and differentiation. The unique proliferative response to bFGF coincided with upregulation of its receptor, fibroblast growth factor receptor (fgfr-1), and downregulation of erythropoietin receptor (EpoR) gene expression. Studies of primary EryP cells derived from early EBs, when tested in a colony-formation assay, also provided evidence for the mitogenic role of bFGF in concert with Epo.

Animals↗
PubMed1998

Production and characterization of monoclonal antibodies to oxidized LDL.

Oxidized low density lipoprotein (LDL) seems to take a part in atherogenesis through direct interactions with macrophages, endothelial cells, and smooth muscle cells, and is thought to participate in renal glomerular injury. For the purpose of illustrating the role of oxidized LDL in the human diseases, monoclonal antibodies were developed and characterized, recognizing oxidized LDL-specific epitopes that do not exist on native LDL. LDL was oxidized by the incubation with CuSO4, and used as immunogen. Splenocytes from the immunized mouse and mouse myeloma cells were fused to produce hybridomas, which were screened for the secretion of oxidized LDL-specific antibodies. Immunoblot analysis and binding affinity assay showed that these monoclonal antibodies recognize malondialdehyde-conjugated peptide epitopes.

Antibodies, Monoclonal↗
PubMed1998

Magnetic resonance studies of intramuscular interferon beta-1a for relapsing multiple sclerosis. The Multiple Sclerosis Collaborative Research Group.

The Multiple Sclerosis Collaborative Research Group trial was a double-blind, randomized, multicenter, phase III, placebo-controlled study of interferon beta-1a (IFNbeta-1a; AVONEX) in relapsing forms of multiple sclerosis. Initial magnetic resonance imaging results have been published; this report provides additional results. Treatment with IFNbeta-1a, 30 microg once weekly by intramuscular injection, resulted in a significant decrease in the number of new, enlarging, and new plus enlarging T2 lesions over 2 years. The median increase in T2 lesion volume in placebo and IFNbeta-1a patients was 455 and 152 mm3, respectively, at 1 year and 1,410 and 628 mm3 at 2 years, although the treatment group differences did not reach statistical significance. For active patients, defined as those with gadolinium enhancement at baseline, the median change in T2 lesion volume in placebo and IFNbeta-1a patients was 1,578 and -12 mm3 and 2,980 and 1,285 mm3 at 1 and 2 years, respectively. Except for a minimal correlation of 0.30 between relapse rate and the number of gadolinium-enhanced lesions, correlations between MR and clinical measures at baseline and throughout the study were in general poor. Once weekly intramuscular IFNbeta-1a appears to impede the development of multiple sclerosis lesions at an early stage and has a favorable impact on the long-term sequelae of these inflammatory events as indicated by the slowed accumulation of T2 lesions.

Brain↗