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Biomedical subjects

M Yin

Publications and source records attributed to M Yin.

At least 109 records · Page 6Linked to original sources
PubMed1993

Artificial duplication of the R67 dihydrofolate reductase gene to create protein asymmetry. Effects on protein activity and folding.

R67 dihydrofolate reductase (DHFR), encoded by an R plasmid, provides resistance to the antibacterial drug trimethoprim. This enzyme does not exhibit any structural or sequence homologies with chromosomal DHFR. A recent crystal structure of tetrameric R67 DHFR (D. Matthews, X. Nguyen-huu, and N. Narayana, personal communication) shows a single pore traversing the length of the molecule. Numerous physical and kinetic experiments suggest the pore is the active site. Since the center of the pore possesses exact 222 symmetry, mutagenesis of residues designed to explore substrate binding will probably also affect cofactor binding. As a first step in breaking this inevitable symmetry in R67 DHFR, the gene has been duplicated. The protein product, R67 DHFRdouble, is twice the molecular mass of native R67 DHFR and is fully active with kcat = 1.2 s-1, Km(NADPH) = 2.7 microM and Km(dihydrofolate) = 6.3 microM. Equilibrium unfolding studies in guanidine-HCl indicate R67 DHFRdouble is more stable than native R67 DHFR at physically reasonable protein concentrations. Microcalorimetry studies show native R67 DHFR undergoes fully reversible thermal unfolding. Unfolding can be described by a two-state process since a ratio of delta Hcalorimetric to delta Hvan't Hoff equals 0.96. In contrast, thermal unfolding of R67 DHFRdouble is not fully reversible and possesses an oligomerization component introduced by the gene duplication event.

Amino Acid Sequence↗
PubMed1993

Structures of thrombin complexes with a designed and a natural exosite peptide inhibitor.

The structures of two hirudin-based fibrinogen recognition exosite peptide inhibitors with significantly different sequences complexed with alpha-thrombin at a site distinct from the active site (exosite) have been determined crystallographically at 2.2 and 2.3 A resolution. One is a designed synthetic peptide with some nonconventional amino acid residues (MDL-28050), and the other is a natural COOH-terminal peptide isolated from the leech Hirudinaria manillensis (hirullin P18). The structures have been refined by restrained least squares methods to R values of 0.161 and 0.155, respectively. The first stretch of each peptide, corresponding to hirudin 55-59, associates with thrombin similar to hirudin and hirugen (hirudin 53-64). Although the remaining residues of the inhibitors interact with and bind to thrombin, the binding is accomplished. through a rigid body conformational adjustment of the peptide with respect to the conformation displayed by hirudin and hirugen (40 degrees rotation about the Ile59, CA-C bond). This causes the side groups of cyclohexylalanine 64' of MDL-28050 and Ile60, of hirullin to point in the opposite direction of the all important Tyr63, ring of hirudin and hirugen but permits the residues to penetrate and interact with the 3(10) turn hydrophobic binding pocket of thrombin. Thus, the hydrophobic interaction is accomplished in a different way by virtue of the substrate conformational readjustment. The results show that the first stretch of peptide makes concerted and efficient binding interactions with thrombin, and the peptide positions of the inhibitors are fairly specific and homologous so that the stretch appears to be related to specific recognition associated with the exosite. The relative flexibility of structure and sequence of the second stretch is a display of tolerance of imprecision by thrombin in its COOH-terminal hydrophobic association with hirudin-based inhibitors.

Amino Acid Sequence↗
PubMed1993

The presence of mast cells in the human endometrium pre- and post-insertion of intrauterine devices.

A study of the density of mast cells in the human endometrium was carried out on biopsy specimens prepared for light microscopy in 87 cases with three types of IUDs (stainless steel ring SS-type, copper Cu-T 220 and LNG-IUD levonorgestrel-releasing device) pre- and post-insertion. The results revealed that, in general, there was an increase of mast cells after 3 to 24 months' use of IUD, independent of type (p < 0.01 when compared with the pre-insertion value). The increase in number of mast cells was most prominent in women having used the Cu-T220 IUD for 24 months (p < 0.05 when compared with the SS-IUD and p < 0.01 when compared with the LNG-IUD). The difference between the SS-IUD and the LNG-IUD as to the number of mast cells was not significant. No significant difference was found between the "bleeders" and "non-bleeders" in any of the three types of IUDs. It is noteworthy that patients using the Cu-T220-IUD had the highest percentage of patients with abnormal bleeding (> 50%) and that this group also had the highest density of mast cells per mm2 after 24 months' use. Although no significant difference with regard to the density of mast cells could be found between the "bleeders" and the "non-bleeders" in the present study, the number of "bleeders" of the three study groups is usually small and sometimes this number does not allow an adequate statistical analysis for comparison. Further investigations, involving larger number of IUD users, may yield a better understanding with regard to the potential relationship between the number of bleeding episodes and the density of mast cells in the human endometrium.

Adult↗
PubMed1993

Clonogenic potential of myeloid leukaemia cells in vitro is restricted to leukaemia cells expressing the CD34 antigen.

Cells from patients with acute myeloid leukaemia (AML) or chronic myeloid leukaemia (CML) were separated into CD34-enriched and CD34-depleted subpopulations. The clonogenic capacities of these two subpopulations were then compared to each other and to the original unseparated cell population. In every study, the CD34-enriched subpopulation demonstrated a substantial increase in clonogenicity in vitro in comparison with the original cell population, while the reverse was the case for the CD34-depleted subpopulations. For reasons not clear at present, the enrichment for clonogenic cells far exceeded the enrichment for cells expressing the CD34 antigen. Additionally, the clonogenic potential was found to be unrelated to the level of myc expression in the various cell populations.

Antigens, CD↗
PubMed1993

Effects of rhGM-CSF on myeloid clonogenic cells in acute myelogenous leukemia patients.

The effects of rhGM-CSF in vivo on the myeloid clonogenic cells present in 6 AML patients was evaluated. The relative number of clonogenic cells fell in 4 of the 6 patients. The effects of rhGM-CSF on the percentage of clonogenic cells in S phase and the sensitivity of clonogenic cells to cytosine arabinoside varied among the patients. These effects were not related to the effects of rhGM-CSF on the white blood cell count or on the proliferative rate of the leukemia cell population as a whole.

Adult↗
PubMed1992

Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease.

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.

Animals↗
PubMed1992

Comparison of two methods for concentrating CD34+ cells from patients with acute non-lymphocytic leukemia.

The aim of the present study was to compare two different methods for obtaining CD34+ cells from the peripheral blood or the bone marrow of patients with acute non-lymphocytic leukemia (ANLL). Twenty-two samples, obtained from 19 patients, were density cut (Ficoll-Hypaque 1.077) and, after incubation with My10 antibody, separated by panning or by immunomagnetic beads. Immunomagnetic beads provided a significantly better separation than panning, either in terms of concentration of CD34+ cells (85.5 +/- 11.6% vs. 55.7 +/- 25.0%, p = 0.003) or in terms of depletion of CD34+ cells (3.9 +/- 8.0% vs. 30.9 +/- 26.3%, p = 0.008). This was consistent with the virtually complete depletion of colony forming cells (CFC) in the CD34 negative fraction and the recovery of virtually all the CFC in the positive fraction in the samples separated by immunomagnetic beads. In conclusion, separation by immunomagnetic beads can allow collection of nearly pure CD34+ and CD34- cell populations from patients with ANLL, thereby facilitating the study of the biological characteristics of these cell populations. Moreover the method is less time consuming than panning and is not toxic to the CFC.

Adolescent↗
PubMed1992

Effects of an IL-1 receptor antagonist on acute myeloid leukemia cells.

The effect of an interleukin 1 receptor antagonist (IL-1ra) on the proliferation of acute myelogenous leukemia (AML) cells was investigated. The antagonist reduced the spontaneous clonogenicity of these cells as well as the clonogenicity of these cells subsequent to exposure to the antagonist. The effects of the IL-1ra on the clonogenicity of leukemia cells was observed even when the antagonist failed to inhibit DNA synthesis by the leukemia cell population as a whole. The data are consistent with the concept that the administration of IL-1ra subsequent to cytotoxic therapy has the potential of slowing the regrowth of leukemia cells thereby potentiating the effects of chemotherapy.

Bromodeoxyuridine↗
PubMed1992

[Studies of cockroachcidal toxin].

A cockroachcidal bacterial isolate CW-W-90-3 was selected by egg yolk agar plate. The isolate produced phospholipase C (PLC) which was pathogenic to the nymph of cockroach. The conditions for production of high level PLC indicated that using LB medium supplement Tween-80 or minimal medium could effectively increase the activity of PLC. The optical phase for production of PLC was in the period of 12-18 hours and below pH8.0. The activity of PLC was reduced along with the culture time until 48 hours. The PLC was resistant to heat. The partially purified PLC from the culture supernatant was assayed by using cockroach nymphes and produced 71.74% mortality.

Animals↗
PubMed1992

Cytogenetic studies of human malignant melanoma cell lines.

Cytogenetic studies were performed on six cell lines derived from three patients suffering from malignant melanomas. The modal chromosome numbers were in the hypotriploid to hypertetraploid ranges and both the numerical and structural aberrations of chromosomes were found. Aberrations were most frequently observed in chromosomes 1, 6 and 7. Deletion of 1q was consistently present in all cell lines, while loss of 6q was observed in two cell lines of case 1. Translocations t (Y; 6) and t (6;?) occurred in one cell line from case 3. An increased number of copies of chromosome 7 was a characteristic feature of the cell lines from case 2. Since positive correlation between the expression of EGF receptors and an increased dosage of chromosome 7 has been reported for malignant melanomas and the gene for EGFR has been mapped to band 7p12-p13, this phenomenon might be of importance for the proliferation of malignant melanoma. The findings of the present study are generally in agreement with the data previously published in the literature, indicating the existence of specific non-random chromosome lesions during melanoma development.

Adult↗
PubMed1991

[Nasal polyps].

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Combined Modality Therapy↗
PubMedDate not supplied

A systemic route for drug loading to lymphatic phagocytes.

Lymph nodes are primary germination and proliferation sites for many types of pathogens. Maintaining therapeutic levels of appropriate chemotherapeutic agents in the lymph node tissue is critical for the treatment of both infection and cancer. This study was intended to develop a systemic route for loading lymph node phagocytes with drugs, using a lymph node specific nanocarrier. The latter is assembled as a 10-15 nm particle with a drug-carrying core and a phagocyte-homing poly(1-->6)-alpha-d-glucose based interface. Biokinetics and microdistribution of the model carrier were investigated in vivo. Nanocarrier accumulation in lymph nodes reached 30-35% dose/g in central lymph nodes, with deposition in various phagocytic cell populations. The latter included cells harboring inhaled microparticles translocated to lymph nodes from the lungs. In view of the nanocarrier ability to transport and release significant amounts of various drug substances, the data suggests feasibility of systemic drug loading to lymphatic phagocytes and, through drug release, to the neighboring cells.

Animals↗