Biomedical subjects

Mian Long

Publications and source records attributed to Mian Long.

11 recordsLinked to original sources

PubMed2006

Probabilistic modeling of rosette formation.

Rosetting, or forming a cell aggregate between a single target nucleated cell and a number of red blood cells (RBCs), is a simple assay for cell adhesion mediated by specific receptor-ligand interaction. For example, rosette formation between sheep RBC and human lymphocytes has been used to differentiate T cells from B cells. Rosetting assay is commonly used to determine the interaction of Fc gamma-receptors (FcgammaR) expressed on inflammatory cells and IgG coated on RBCs. Despite its wide use in measuring cell adhesion, the biophysical parameters of rosette formation have not been well characterized. Here we developed a probabilistic model to describe the distribution of rosette sizes, which is Poissonian. The average rosette size is predicted to be proportional to the apparent two-dimensional binding affinity of the interacting receptor-ligand pair and their site densities. The model has been supported by experiments of rosettes mediated by four molecular interactions: FcgammaRIII interacting with IgG, T cell receptor and coreceptor CD8 interacting with antigen peptide presented by major histocompatibility molecule, P-selectin interacting with P-selectin glycoprotein ligand 1 (PSGL-1), and L-selectin interacting with PSGL-1. The latter two are structurally similar and are different from the former two. Fitting the model to data enabled us to evaluate the apparent effective two-dimensional binding affinity of the interacting molecular pairs: 7.19x10(-5) microm4 for FcgammaRIII-IgG interaction, 4.66x10(-3) microm4 for P-selectin-PSGL-1 interaction, and 0.94x10(-3) microm4 for L-selectin-PSGL-1 interaction. These results elucidate the biophysical mechanism of rosette formation and enable it to become a semiquantitative assay that relates the rosette size to the effective affinity for receptor-ligand binding.

Animals↗

PubMed2006

Kinetics of receptor-ligand interactions in immune responses.

Receptor-ligand interactions in blood flow are crucial to initiate the biological processes as inflammatory cascade, platelet thrombosis, as well as tumor metastasis. To mediate cell adhesions, the interacting receptors and ligands must be anchored onto two apposing surfaces of two cells or a cell and a substratum, i.e., the two-dimensional (2D) binding, which is different from the binding of a soluble ligand in fluid phase to a receptor, i.e., three-dimensional (3D) binding. While numerous works have been focused on 3D kinetics of receptor-ligand interactions in immune systems, 2D kinetics and its regulations have less been understood, since no theoretical framework and experimental assays have been established until 1993. Not only does the molecular structure dominate 2D binding kinetics, but the shear force in blood flow also regulates cell adhesions mediated by interacting receptors and ligands. Here we provided the overview of current progresses in 2D bindings and regulations. Relevant issues of theoretical frameworks, experimental measurements, kinetic rates and binding affinities, and force regulations, were discussed.

Animals↗

PubMed2005

Flavonoid of Drynaria fortunei protects against acute renal failure.

The flavonoid fraction (FF) from Drynaria fortunei was investigated to determine its biological activity expression in three acute renal failure animal models. Guinea pigs received 100 mg/kg of gentamicin (GM group), 100 mg/kg of GM plus 10 mg/kg of FF (GMFF group), 10 mg/kg of FF (FF group) or saline (saline group) intramuscularly for 14 days. The blood urea nitrogen (BUN) and creatinine levels were found to be significantly higher in the GM group (22.70+/-3.84 mg/dL, 0.68+/-0.05 mg/dL) than in the GMFF group (17.10+/-1.04 mg/dL, 0.58+/-0.09 mg/dL), the FF group (17.40+/-1.01 mg/dL, 0.49+/-0.20 mg/dL) and the saline group (17.50+/-1.22 mg/dL, 0.50+/-0.02 mg/dL). Mice were treated once with 6 mg/kg of mercuric chloride, followed by 10 mg/kg of FF or saline. On days 3, 4 and 5, BUN and creatinine levels were found to be significantly higher in the HgCl2-saline group (74.00+/-39.20 mg/dL, 59.30+/-31.20 mg/dL, 74.00+/-37.30 mg/dL and 0.53+/-0.17 mg/dL, 0.48+/-0.15 mg/dL 0.33+/-0.15 mg/dL) than in the HgCl2-FF group (19.50+/-4.90 mg/dL, 43.00+/-26.30 mg/dL, 38.50+/-13.80 mg/dL and 0.23+/-0.05 mg/dL, 0.30+/-0.12 mg/dL, 0.15+/-0.06 mg/dL).After surgery for 5/6-nephrectomy, ten mice received FF at a dose of 10 mg/kg/day and eight received saline for 42 days. The saline group survived for 12-62 days and the FF group survived for 20-320 days. The FF group had a significantly longer survival time than the saline group (p<0.05). Regeneration of kidney tubular cells and significantly enlarged convoluted tubules were noted in the pathology study of the FF group. In conclusion, the present study suggests that FF prevents nephrotoxicity, improves kidney function and promotes kidney primary epithelial tubular cell regeneration.

Acute Kidney Injury↗

PubMed2005

[Measuring rupture forces of P-selectin/PSGL-1 bonds using an optical trap assay].

Selectin/ligand interaction plays an important role in such biological processes as inflammatory reaction, tumor metastasis, etc. External forces affect dissociation of receptor-ligand bonds. A novel approach, upon optical trap technique, was developed in this study to investigate the dissociation of P-selectin/PSGL-1 (P-Selectin Glycoprotein Ligand 1) bindings. Stiffness of optical trap was calibrated with laser power using a viscous drag method. While P-selectin and PSGL-1 molecules were functionally coated on surfaces of glass beads, respectively, the dissociation of interacting molecule bond was studied by measuring the rupture force distribution. It was found that most probable rupture force increased with loading rate at < 25 pN/s. These results complemented and validated the current theory at low loading rates.

Humans↗

PubMed2005

Forced dissociation of selectin-ligand complexes using steered molecular dynamics simulation.

Selectin-ligand interactions are crucial to such biological processes as inflammatory cascade or tumor metastasis. How transient formation and dissociation of selectin-ligand bonds in blood flow are coupled to molecular conformation at atomic level, however, has not been well understood. In this study, steered molecular dynamics (SMD) simulations were used to elucidate the intramolecular and intermolecular conformational evolutions involved in forced dissociation of three selectin-ligand systems: the construct consisting of P-selectin lectin (Lec) and epidermal growth factor (EGF)-like domains (P-LE) interacting with synthesized sulfoglycopeptide or SGP-3, P-LE with sialyl Lewis X (sLe(X)), and E-LE with sLe(X). SMD simulations were based on newly built-up force field parameters including carbohydrate units and sulfated tyrosine(s) using an analogy approach. The simulations demonstrated that the complex dissociation was coupled to the molecular extension. While the intramolecular unraveling in P-LE-SGP-3 system mainly resulted from the destroy of the two anti-parallel beta sheets of EGF domain and the breakage of hydrogen-bond cluster at the Lec-EGF interface, the intermolecular dissociation was mainly determined by separation of fucose (FUC) from Ca2+ ion in all three systems. Conformational changes during forced dissociations depended on pulling velocities and forces, as well as on how the force was applied. This work provides an insight into better understanding of conformational changes and adhesive functionality of selectin-ligand interactions under external forces.

Animals↗

PubMed2004

Quantifying the effects of molecular orientation and length on two-dimensional receptor-ligand binding kinetics.

Surface presentation of adhesion receptors influences cell adhesion, although the mechanisms underlying these effects are not well understood. We used a micropipette adhesion frequency assay to quantify how the molecular orientation and length of adhesion receptors on the cell membrane affected two-dimensional kinetic rates of interactions with surface ligands. Interactions of P-selectin, E-selectin, and CD16A with their respective ligands or antibody were used to demonstrate such effects. Randomizing the orientation of the adhesion receptor or lowering its ligand- and antibody-binding domain above the cell membrane lowered two-dimensional affinities of the molecular interactions by reducing the forward rates but not the reverse rates. In contrast, the soluble antibody bound with similar three-dimensional affinities to cell-bound P-selectin constructs regardless of their orientation and length. These results demonstrate that the orientation and length of an adhesion receptor influences its rate of encountering and binding a surface ligand but does not subsequently affect the stability of binding.

Animals↗

PubMed2004

Flavanoid of Drynaria fortunei protects against gentamicin ototoxicity.

A flavanoid fraction (FF) from Drynaria fortunei, was investigated to see if it has the protective and ameliorative effects against gentamicin (GM) ototoxicity in guinea pigs (n = 36). Eleven (GM-group) animals received GM 100 mg/kg/day. Eleven (GMFF-group) animals received the same dose of GM but 2 days prior were dosed with FF (10 mg/kg/day) for 2 weeks. Seven (S-group) animals received saline and seven (FF-group) animals received the same dose of FF as the GMFF-group. The thresholds of tone-burst auditory evoked response (ABR) at 2 k, 8 k, and 32 k Hz were determined to be as follows: GM-group: 90 dB, 92 dB and 72 dB, GMFF-group: 30 dB, 37 dB and 38 dB, FF-group: 28 dB, 25 dB and 29 dB, S-group: 30 dB, 28 dB and 39 dB. The GM-group had a significantly higher hearing threshold than the other groups (p < 0.05). The GMFF- and FF-groups had hearing thresholds similar to the S-groups (p > 0.1). Repair of damaged hair cells was observed histologically. The percentage of the damaged outer hair cells (OHC) and inner hair cells (IHC) were determined to be as follows: GM-group: 43% and 20%, GMFF-group: 20% and 2%, FF-group: 9% and 2% and S-group: 4% and 1%. The GMFF-group showed less damage to the OHC (p > 0.05) and significantly less damage to the IHC (p < 0.05) than the GM-group. FF did not change the antimicrobial activity of GM and it did not show any intrinsic antibacterial effect. FF did not affect the kinetics of GM during the course of the experiment.

Animals↗

PubMed2003

Direct observation of catch bonds involving cell-adhesion molecules.

Bonds between adhesion molecules are often mechanically stressed. A striking example is the tensile force applied to selectin-ligand bonds, which mediate the tethering and rolling of flowing leukocytes on vascular surfaces. It has been suggested that force could either shorten bond lifetimes, because work done by the force could lower the energy barrier between the bound and free states ('slip'), or prolong bond lifetimes by deforming the molecules such that they lock more tightly ('catch'). Whereas slip bonds have been widely observed, catch bonds have not been demonstrated experimentally. Here, using atomic force microscopy and flow-chamber experiments, we show that increasing force first prolonged and then shortened the lifetimes of P-selectin complexes with P-selectin glycoprotein ligand-1, revealing both catch and slip bond behaviour. Transitions between catch and slip bonds might explain why leukocyte rolling on selectins first increases and then decreases as wall shear stress increases. This dual response to force provides a mechanism for regulating cell adhesion under conditions of variable mechanical stress.

Antibodies, Monoclonal↗

PubMed2002

Measuring receptor/ligand interaction at the single-bond level: experimental and interpretative issues.

There is increased interest in measuring kinetic rates, lifetimes, and rupture forces of single receptor/ligand bonds. Valuable insights have been obtained from previous experiments attempting such measurements. However, it remains difficult to know with sufficient certainty that single bonds were indeed measured. Using exemplifying data, evidence supporting single-bond observation is examined and caveats in the experimental design and data interpretation are identified. Critical issues preventing definitive proof and disproof of single-bond observation include complex binding schemes, multimeric interactions, clustering, and heterogeneous surfaces. It is concluded that no single criterion is sufficient to ensure that single bonds are actually observed. However, a cumulative body of evidence may provide reasonable confidence.

Cell Adhesion↗

PubMed2002

Mechanical properties of hepatocellular carcinoma cells.

AIM: To study the viscoelastic properties of human hepatocytes and hepatocellular carcinoma (HCC) cells under cytoskeletal perturbation, and to further to study the viscoelastic properties and the adhesive properties of mouse hepatoma cells (HTC) in different cell cycle. METHODS: Micropipette aspiration technique was adopted to measure viscoelastic coefficients and adhesion force to collagen coated surface of the cells. Three kinds of cytoskeleton perturbing agents, colchicines (Col), cytochalasin D (CD) and vinblastine (VBL), were used to treat HCC cells and hepatocytes and the effects of these treatment on cell viscoelastic coefficients were investigated. The experimental results were analyzed with a three-element standard linear solid. Further, the viscoelastic properties of HTC cells and the adhesion force of different cycle HTC cells were also investigated. The synchronous G(1) and S phase cells were achieved through thymine-2-desoryriboside and colchicines sequential blockage method and thymine-2-desoryriboside blockage method respectively. RESULTS: The elastic coefficients, but not viscous coefficient of HCC cells (K(1)=103.6+/-12.6N.m(-2), K(2)=42.5 +/ 10.4N.m(-2), mu=4.5 +/- 1.9Pa.s), were significantly higher than the corresponding value for hepatocytes (K(1)=87.5 +/- 12.1N.m(-2), K(2)=33.3+/-10.3N.m(-2), mu=5.9+/-3.0Pa.s, P<0.01). Upon treatment with CD, the viscoelastic coefficients of both hepatocytes and HCC cells decreased consistently, with magnitudes for the decrease in elastic coefficients of HCC cells (K(1): 68.7 N.m(-2) to 81.7N.m(-2), 66.3% to 78.9%; K(2): 34.5N.m(-2) to 37.1N.m(-2), 81.2% to 87.3%, P<0.001) larger than those for normal hepatocytes (K(1): 42.6N.m(-2) to 49.8N.m(-2), 48.7% to 56.9%; K(2): 17.2N.m(-2) to 20.4N.m(-2), 51.7% to 61.3%, P<0.001). There was a little decrease in the viscous coefficient of HCC cells (2.0 to 3.4Pa.s, 44.4 to 75.6%, P<0.001) than that for hepatocytes (3.0 to 3.9Pa.s, 50.8 to 66.1% P<0.001). Upon treatment with Col and VBL, the elastic coefficients of hepatocytes generally increased or tended to increase while those of HCC cells decreased. HTC cells with 72.1% of G(1) phase and 98.9% of S phase were achieved and high K(1), K(2) value and low mu value were the general characteristics of HTC cells. G(1) phase cells had higher K(1) value and lower mu value than S phase cells had, and G(1) phase HTC cells had stronger adhesive forces ((275.9 +/- 232.8) x 10(-10)N) than S phase cells ((161.2 +/- 120.4) x 10(-10)N, P<0.001). CONCLUSION: The difference in both the pattern and the magnitude of the effect of cytoskeletal perturbing agent on the viscoelastic properties between HCC cells and hepatocytes may reflect differences in the state of the cytoskeleton structure and function and in the sensitivity to perturbing agent treatment between these two types of cells. Change in the viscoelastic properties of cancer cells may affect significantly tumor cell invasion and metastasis as well as interactions between tumor cells and their micro-mechanical environments.

Animals↗

PubMed2002

Adhesive properties of hepatoma cells to collagen IV coated surfaces.

OBJECTIVES: To quantitatively study the adhesive properties of hepatoma cells to collagen IV coated artificial basement membrane and to investigate the relevance of cell adhesive forces to the concentration of collagen IV. METHODS: Synchronous G1 and S phase cells were achieved using thymine-2-desoxyriboside and cochicine sequential blockage method and double thymine-2-desoxyriboside blockage method respectively. The adhesive forces of hepatoma cells were investigated by micropipette aspiration technique. RESULTS: The adhesive forces of hepatoma cells to artificial basement membrane were (107.78+/-65.44)x10(-10)N, (182.60+/-107.88)x10(-10)N, (298.91+/-144.13)x10(-10)N when the concentration of the membrane coated by 1, 2, 5 microg/ml collagen IV respectively (P<0.001). The adhesive forces of G1 and S phases hepatoma cells to artificial basement membrane were (275.86+/-232.80)x10(-10)N and (161.16+/-120.40)x10(-10)N respectively when the concentration of the membrane coated by 5 microg/ml collagen IV (P<0.001). CONCLUSIONS: The adhesive forces of hepatoma cells to artificial basement membrane in direct proportion to the concentration of collagen IV suggests that the increase of basement membrane might be conducive to the chemotactic motion and adhesiveness of tumor cells. G1 phase cells are more capable of adhering to basement membrane than S phase cells. Hepatoma cells, especially G1 phase cells, may survive in blood circulation, and sequest and adhere in microcirculation, and get through basement membrane for remote metastasis.

Animals↗