Biomedical subjects

K Zygourakis

Publications and source records attributed to K Zygourakis.

11 recordsLinked to original sources

PubMed2000

Endothelial cell migration on surfaces modified with immobilized adhesive peptides.

Endothelial cell (EC) migration has been studied on aminophase surfaces with covalently bound RGDS and YIGSRG cell adhesion peptides. The fluorescent marker dansyl chloride was used to quantify the spatial distribution of the peptides on the modified surfaces. Peptides appeared to be distributed in uniformly dispersed large clusters separated by areas of lower peptide concentrations. We employed digital time-lapse video microscopy and image analysis to monitor EC migration on the modified surfaces and to reconstruct the cell trajectories. The persistent random walk model was then applied to analyze the cell displacement data and compute the mean root square speed, the persistence time, and the random motility coefficient of EC. We also calculated the time-averaged speed of cell locomotion. No differences in the speed of cell locomotion on the various substrates were noted. Immobilization of the cell adhesion peptides (RGDS and YIGSRG), however, significantly increased the persistence of cell movement and, thus, the random motility coefficient. These results suggest that immobilization of cell adhesion peptides on the surface of implantable biomaterials may lead to enhanced endothelization rates.

Amino Acid Sequence↗

PubMed1999

Migration of lymphocytes on fibronectin-coated surfaces: temporal evolution of migratory parameters.

Lymphocytes typically interact with implanted biomaterials through adsorbed exogenous proteins. To provide a more complete characterization of these interactions, analysis of lymphocyte migration on adsorbed extracellular matrix proteins must accompany the commonly performed adhesion studies. We report here a comparison of the migratory and adhesion behavior of Jurkat cells (a T lymphoblastoid cell line) on tissue culture treated and untreated polystyrene surfaces coated with various concentrations of fibronectin. The average speed of cell locomotion showed a biphasic response to substrate adhesiveness for cells migrating on untreated polystyrene and a monotonic decrease for cells migrating on tissue culture-treated polystyrene. A modified approach to the persistent random walk model was implemented to determine the time dependence of cell migration parameters. The random motility coefficient showed significant increases with time when cells migrated on tissue culture-treated polystyrene surfaces, while it remained relatively constant for experiments with untreated polystyrene plates. Finally, a cell migration computer model was developed to verify our modified persistent random walk analysis. Simulation results suggest that our experimental data were consistent with temporally increasing random motility coefficients.

Adsorption↗

PubMed1998

Bioenergetics of rat prostate cancer cell migration.

BACKGROUND: Increased cell motility and increased glycolysis are two well-known hallmarks of cancer. We undertook these studies to determine whether increased glycolysis is required for prostate cancer cell locomotion. METHODS: We studied the highly metastatic MatLu cell line, which is a variant of the Dunning R-3327 rat prostate adenocarcinoma model. Using videomicroscopy and computer image analysis, we compared the speed of migration of cells grown in serum-free medium in either the presence or absence of glucose. RESULTS: We found that cells grown in glucose-free, conditioned medium maintained speeds of migration and intracellular ATP levels for 24 hr which were equivalent to those of cells grown in conditioned medium containing glucose. In contrast, migration was significantly inhibited by growth in glucose-free, unconditioned medium. We also tested the effect of antimycin A and rotenone, two inhibitors of mitochondrial electron transport, on cell migration and ATP levels. Antimycin A had no significant effect on either feature, while rotenone slightly inhibited cell migration without affecting ATP levels. CONCLUSIONS: 1) Glycolysis is not necessary for rat prostate cancer cell locomotion in the presence of conditioned medium. 2) MatLu cells grown in the absence of both serum and conditioned medium require glucose to maintain cellular ATP levels and cell migration. 3) MatLu cells in conditioned medium adapt to inhibition of glycolysis or mitochondrial respiration by increasing the activity of the uninhibited pathway.

Adenocarcinoma↗

PubMed1997

A model for the kinetics of homotypic cellular aggregation under static conditions.

We present the formulation and testing of a mathematical model for the kinetics of homotypic cellular aggregation. The model considers cellular aggregation under no-flow conditions as a two-step process. Individual cells and cell aggregates 1) move on the tissue culture surface and 2) collide with other cells (or aggregates). These collisions lead to the formation of intercellular bonds. The aggregation kinetics are described by a system of coupled, nonlinear ordinary differential equations, and the collision frequency kernel is derived by extending Smoluchowski's colloidal flocculation theory to cell migration and aggregation on a two-dimensional surface. Our results indicate that aggregation rates strongly depend upon the motility of cells and cell aggregates, the frequency of cell-cell collisions, and the strength of intercellular bonds. Model predictions agree well with data from homotypic lymphocyte aggregation experiments using Jurkat cells activated by 33B6, an antibody to the beta 1 integrin. Since cell migration speeds and all the other model parameters can be independently measured, the aggregation model provides a quantitative methodology by which we can accurately evaluate the adhesivity and aggregation behavior of cells.

Antibodies↗

PubMed1996

Induction of homotypic lymphocyte aggregation: evidence for a novel activation state of the beta1 integrin.

Intercellular adhesion of Jurkat lymphocytic cells was investigated by use of monoclonal antibodies 33B6 and 18D3, which bind to the beta1 integrin receptor. 33B6 induced homotypic aggregation of Jurkat cells, whereas 18D3 inhibited this aggregation. Jurkat cells could he induced to aggregate at low 33B6 concentrations corresponding to 5% beta1 integrin site occupancy, and the rate of aggregation was maximum at 30% occupancy. Simultaneous addition of mAb 18D3 and 33B6 demonstrated that the two antibodies mediate changes in the beta1 integrin activation state that are competitive in nature. Aggregation through beta1 integrin induced by 33B6 was reversed by subsequent addition of 18D3. To further examine the mechanism by which 33B6 and 18D3 affect cell adhesion function, we explored the binding of monoclonal antibody (mAb) 15/7. This mAb recognizes an activation epitope of the beta1 integrin and has been shown to sustain cell adhesion to vascular cell adhesion molecule 1 (VCAM-1) and fibronectin. Activation of Jurkat cells with Mn2+ caused a 2.5-fold increase in 15/7 binding but did not increase binding of 33B6. 33B6 partially blocked 15/7 binding to beta1 integrin on unstimulated and Mn2+-activated Jurkat cells. 18D3 did not affect mAb 15/7 binding. These results indicate that 33B6 and 18D3 modulated homotypic aggregation by inducing a novel activation state of the very late activation integrin distinct from the state recognized by 15/7, which supports cell binding to VCAM-1 and fibronectin.

Antibodies, Monoclonal↗

PubMed1996

Computer-aided design of bioerodible devices with optimal release characteristics: a cellular automata approach.

The development of a computational tool to design bioerodible devices with optimal release characteristics is presented. This computational tool uses cellular automata and parallel iterations to model and simulate the release of bioactive agents (drugs) from bioerodible matrices. The simulations can accurately model surface erosion processes in multicomponent systems of arbitrary geometry and with different dissolution rates for each component. Simulation results are analysed to show how the overall release rates are affected by the intrinsic dissolution rates, drug loading, porosity and the dispersion of the drug in the bioerodible matrix. A strongly non-linear dependence of release rates on drug loading and the intrinsic dissolution rates of the solid components is obtained and the effects of phase dispersion on the variability of release rates are elucidated. Finally, guidelines are presented for screening of alternatives to minimize the development effort and experimentation required for designing devices with desired release characteristics.

Biocompatible Materials↗

PubMed1995

A cellular automaton model for the proliferation of migrating contact-inhibited cells.

A cellular automaton is used to develop a model describing the proliferation dynamics of populations of migrating, contact-inhibited cells. Simulations are carried out on two-dimensional networks of computational sites that are finite-state automata. The discrete model incorporates all the essential features of the cell locomotion and division processes, including the complicated dynamic phenomena occurring when cells collide. In addition, model parameters can be evaluated by using data from long-term tracking and analysis of cell locomotion. Simulation results are analyzed to determine how the competing processes of contact inhibition and cell migration affect the proliferation rates. The relation between cell density and contact inhibition is probed by following the temporal evolution of the population-average speed of locomotion. Our results show that the seeding cell density, the population-average speed of locomotion, and the spatial distribution of the seed cells are crucial parameters in determining the temporal evolution of cell proliferation rates. The model successfully predicts the effect of cell motility on the growth of isolated megacolonies of keratinocytes, and simulation results agree very well with experimental data. Model predictions also agree well with experimentally measured proliferation rates of bovine pulmonary artery endothelial cells (BPAE) cultured in the presence of a growth factor (bFGF) that up-regulates cell motility.

Algorithms↗

PubMed1993

Analysis of lymphocyte aggregation using digital image analysis.

We present the development and testing of a novel assay of lymphocyte adhesion based on time-resolved morphological measurements of intercellular aggregation. Homotypic lymphocyte aggregation is induced according to various protocols and monitored for several hours using video microscopy and time-lapse recording. Digital images of the aggregating cell population are acquired and analyzed to obtain the size distribution and the shape of cell aggregates. By following the temporal evolution of the size distribution of aggregates, the rates of aggregation events can be accurately quantified and compared. In addition, an analysis of the two- and three-dimensional structures of the aggregates using appropriately defined shape factors allows comparisons of mechanical binding strengths and cytoskeletal activity. To demonstrate the capabilities of the assay, we present results from a series of aggregation experiments with Jurkat cells treated with 33B6, 19H8, IC9, and 20E4 monoclonal antibodies. These monoclonal antibodies bind to various epitopes of known adhesion molecules and induce aggregation phenomena that proceed at different rates. Our results show that the assay has small repeatability error and is sensitive enough to compare aggregation events induced through distinct molecular epitopes. Used in conjunction with current biochemical detection assays and adhesion pathway modulation experiments, the developed assay will facilitate the study of cellular adhesion and aggregation mechanisms.

Antibodies, Monoclonal↗

PubMed1993

Analysis of lymphocyte activation and proliferation by video microscopy and digital imaging.

Video microscopy and digital imaging were used as a noninvasive method to quantitatively analyze lymphocyte activation and proliferation. This method takes advantage of the fact that upon activation lymphocytes blast and become significantly larger before proliferating. The mean cell sizes of T lymphocytes in an activation kinetics assay were measured by digital image analysis and compared to [3H]-thymidine incorporation of cells under the same treatment. An increase in cell size was observed before [3H]-thymidine incorporation; therefore the digital imaging assay is more sensitive in determining the earliest time-point of activation. Also, the digital imaging assay was comparable to the [3H]-thymidine incorporation assay in providing information about the extent and rates of T lymphocyte proliferation. Cellular DNA was stained with propidium iodide to show that the larger blasting cells in the population of activated T lymphocytes were indeed the cells that accounted for the increase in DNA synthesis and thus an increase in cell size can be correlated with activation.

Analog-Digital Conversion↗

PubMedDate not supplied

A quantitative assay for intercellular aggregation.

In an earlier communication (Munn et al., J Immunol. Methods 166: 11-25, 1993), we presented the initial development of a quantitative assay for monitoring the rates of cellular aggregation based on digital image processing and video microscopy. This study describes some important enhancements and modifications to the procedure. A new index is introduced to characterize the three-dimensional morphology of the aggregates. This index is based on temporal changes in the projected area of the cells and cell aggregates during the course of the experiment. By drawing an analogy with the kinetic theory of gases, we have also introduced a procedure to normalize for variations in cell seeding density among different experiments. In addition, the image analysis technique has been improved by introducing a background subtraction algorithm to remove illumination defects and an adaptive segmentation procedure. These improvements allowed us to completely automate the image analysis procedure, thus minimizing user intervention and improving the reproducibility of the measurements. The enhanced visual assay is evaluated using some recent results from our studies on homotypic lymphocyte aggregation.

Cell Aggregation↗

PubMedDate not supplied

Characterization of endothelial cell locomotion using a Markov chain model.

A Markov chain model was developed to characterize the two-dimensional locomotion of bovine pulmonary artery endothelial (BPAE) cells cultured with or without basic fibroblast growth factor (bFGF). This model provides a detailed description of the migration process by computing the following locomotory parameters: (i) the speed of cell locomotion; (ii) the expected duration of cell movement in any given direction; (iii) the probability distribution of turn angles that will decide the next direction of cell movement; (iv) the frequency of cell stops; and (v) the duration of cell stops. Eight directional states and a stationary state were used in our Markov analysis. From cell trajectory data, the transition probabilities among the various states and the waiting times for the directional and the stationary states were computed. The steady-state probabilities were also calculated to obtain the ultimate direction of cell motion and, thus, determine whether cell motion was random. Our results showed how the addition of bFGF enhanced the locomotory capability of BPAE cells. Cells cultured with 30 ng/mL bFGF had lower probability of moving to the stationary state than those cultured without bFGF. In addition, cells cultured with 30 ng/mL bFGF remained in the stationary state for shorter periods of time than cells cultured without bFGF. In both these cases, however, the transition probabilities from the stationary state to any directional state were uniformly distributed and were not affected by the presence of bFGF.

Algorithms↗