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S K Williams

Publications and source records attributed to S K Williams.

At least 73 records · Page 4Linked to original sources
PubMed1991

Migration of individual microvessel endothelial cells: stochastic model and parameter measurement.

Analysis of cell motility effects in physiological processes can be facilitated by a mathematical model capable of simulating individual cell movement paths. A quantitative description of motility of individual cells would be useful, for example, in the study of the formation of new blood vessel networks in angiogenesis by microvessel endothelial cell (MEC) migration. In this paper we propose a stochastic mathematical model for the random motility and chemotaxis of single cells, and evaluate migration paths of MEC in terms of this model. In our model, cell velocity under random motility conditions is described as a persistent random walk using the Ornstein-Uhlenbeck (O-U) process. Two parameters quantify this process: the magnitude of random movement accelerations, alpha, and a decay rate constant for movement velocity, beta. Two other quantities often used in measurements of individual cell random motility properties--cell speed, S, and persistence time in velocity, Pv--can be defined in terms of the fundamental stochastic parameters alpha and beta by: S =square root (alpha/beta) and Pv = 1/beta. We account for chemotactic cell movement in chemoattractant gradients by adding a directional bias term to the O-U process. The magnitude of the directional bias is characterized by the chemotactic responsiveness, kappa. A critical advantage of the proposed model is that it can generate, using experimentally measured values of alpha, beta and kappa, computer simulations of theoretical individual cell paths for use in evaluating the role of cell migration in specific physiological processes. We have used the model to assess MEC migration in the presence of absence of the angiogenic stimulus acidic fibroblast growth factor (aFGF). Time-lapse video was used to observe and track the paths of cells moving in various media, and the mean square displacement was measured from these paths. To test the validity of the model, we compared the mean square displacement measurements of each cell with model predictions of that displacement. The comparison indicates that the O-U process provides a satisfactory description of the random migration at this level of comparison. Using nonlinear regression in these comparisons, we measured the magnitude of random accelerations, alpha, and the velocity decay rate constant, beta, for each cell path. We consequently obtained values for the derived quantities, speed and persistence time. In control medium, we find that alpha = 250 +/- 100 microns 2h-3 and beta = 0.22 +/- 0.03h-1, while in stimulus medium (control plus unpurified aFGF) alpha = 1900 +/- 720 microns 2h-3 and beta = 0.99 +/- 0.37h-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipose Tissue↗
PubMed1990

Differences in synergistic actions of vasopressin and deoxycorticosterone in rat and rabbit CCD.

We examined the time course of changes in osmotic water permeability (Pf, micron/s), lumen-to-bath 22Na+ flux (Jl----b, pmol.min-1.mm-1), and transepithelial voltage (VT, mV) in response to arginine vasopressin (AVP) in isolated perfused rat and rabbit cortical collecting ducts (CCD). CCDs were isolated from "normal" (untreated) animals and animals 4-14 days after an intramuscular depot injection of deoxycorticosterone pivalate (DOC; 35 mg/rabbit, 5 mg/rat). In the normal rat CCD, 220 pM AVP added to the bathing solution increased Pf from approximately 0 to 981 +/- 120, Jl----b from 24 +/- 5 to 62 +/- 9, and VT from -0.7 +/- 0.6 to -4.0 +/- 0.6 (mean +/- SE; P less than 0.05). The effect of AVP on Pf in DOC-treated rats was not significantly different, but the effects on Jl----b and VT were greater. Jl----b rose from a control value of 78 +/- 16 to 192 +/- 14 with AVP, and VT hyperpolarized from -4.2 +/- 1.6 to -12.2 +/- 0.4. All of these effects of AVP in the normal and DOC-treated rat CCD persisted for greater than or equal to 90-150 min. In DOC-treated rabbit tubules, AVP caused a stable increase in Pf from 9 +/- 6 to 800 +/- 199, which was significantly greater than in normal tubules (379 +/- 32). In the normal rabbit CCD we confirmed previous observations that AVP produces only a transient increase in Na+ absorption and VT; Jl----b increased from 76 +/- 4 to 96 +/- 7 during the period 15-25 min after AVP addition but subsequently fell to 80 +/- 6; VT transiently hyperpolarized from -55 +/- 7 to -64 +/- 8 at 3-8 min after AVP and then fell to -54 +/- 9. In DOC-treated rabbit CCDs, AVP produced no change whatsoever in Jl----b, which was not significantly different from the control value of 99 +/- 7, nor in VT, which was -68 +/- 8 mV. These results indicate fundamental differences in the response of the rat and rabbit CCD to AVP and the presence or absence of synergistic interactions with mineralocorticoids, which may relate to their differing response to other autacoids.

Animals↗
PubMed1990

Chemotaxis of human microvessel endothelial cells in response to acidic fibroblast growth factor.

Migration of microvessel endothelial cells (MEC) in response to angiogenic stimuli is a key aspect of angiogenesis, whether in physiologic or pathologic situations. In this work, we provide a rigorous quantitative assessment of the chemokinetic and chemotactic responses of human MEC to acidic fibroblast growth factor (aFGF). A uniform concentration of 1 micrograms/ml of heparin was included in most experiments to exploit heparin's potentiating effect on aFGF activity. The migration is measured in an under-agarose assay with a linear geometry, and evaluated in terms of the random motility and chemotaxis coefficients, mu and chi, which are defined in a mathematical model. The change in value of mu with changes in aFGF concentration provides a quantitative description of the stimulated random motility response, a process known as chemokinesis. This allows the true directional response in gradients to be quantified by the chemotaxis coefficient, chi, and its variation with attractant concentration. The effect of aFGF on MEC random motility is relatively small, with the random motility coefficient ranging from 4.6 +/- 0.4 x 10(-9) to 9.9 +/- 0.3 x 10(-9) cm2/second (mean +/- SE) over four orders of magnitude of aFGF concentration (10(-11) to 10(-8) M). On the other hand, the magnitude of the chemotaxis coefficient at optimal concentrations is quite large (2600 +/- 750 cm2/second-M around 10(-10) M aFGF), demonstrating a significant degree of MEC directional sensitivity to aFGF gradients. The chemotaxis coefficient shows a biphasic dependence on aFGF concentration, suggestive of a receptor-mediated response in which apparent differences in receptor occupancy govern directional bias. These results provide support for the hypothesis that MEC chemotaxis accounts for the directed microvessel growth observed in angiogenesis.

Cell Movement↗
PubMed1990

Thrombus-free, human endothelial surface in the midregion of a Dacron vascular graft in the splanchnic venous circuit--observations after nine months of implantation.

The addition of an endothelial cell lining to a prosthetic vascular graft may reduce the thrombogenicity of the blood-contacting surface. An endothelialized mesoatrial graft was implanted in a patient with Budd-Chiari syndrome caused by a primary inferior vena caval leiomyosarcoma. During the initial surgery a Dacron vascular graft was preclotted with plasma and then lined with microvascular endothelial cells derived from the patient's subcutaneous adipose tissue. The patient did well initially but 9 months later required resection of a mechanical stricture of the graft that occurred as it passed beneath the costochondral junction. Grossly, the luminal surface of the resected graft was free of thrombus, with a smooth, glistening, white surface. Light microscopy demonstrated a surface layer of cells morphologically consistent with an endothelial cell monolayer, a subendothelial layer composed of extracellular matrix and spindle-shaped cells, and granulation tissue around the Dacron fabric. Immunohistochemistry and electron microscopy confirmed the presence of vascular endothelium on the luminal surface. This report documents the successful achievement of a human endothelial cell monolayer that persisted for 9 months in the midportion of a Dacron vascular graft.

Adult↗
PubMed1990

Electron microscopy of endothelial cell-biopolymer interaction.

Vascular endothelial cells form a natural antithrombogenic lining on all blood vessels. Replacement or bypass of small diameter blood vessels with artificial polymeric grafts has not been clinically acceptable due to the thrombogenic nature of polymeric material. One approach to improving the patency of vascular prosthetic devices has been the establishment of endothelial monolayers on the blood flow surface using the technique known as seeding. Scanning electron microscopy has been a major tool in evaluating the interaction of endothelial cells with polymeric surfaces resulting in a basic understanding of forces and structures regulating endothelium-polymer interactions. In-vitro and in-vivo studies have established the feasibility of using endothelial cell seeding technology in human clinical trials. This tutorial describes the development of endothelial cell seeding technology and illustrates how scanning electron microscopic evaluations have furthered our understanding of endothelial cell-polymer interactions.

Biopolymers↗
PubMed1989

Enhanced adherence of human adult endothelial cells to plasma discharge modified polyethylene terephthalate.

Human adult aortic endothelial cell attachment to polyethyleneterephthalate (PET as mylar film) was examined in vitro. PET was examined in both the unmodified form (PET-) and in a modified form (PET+) that had undergone plasma discharge surface modification (PDSM). These surfaces were compared to unmodified tissue culture polystyrene (PS-). The kinetics of attachment and the force of attachment using the rotating disc were determined as a function of surface and substrate protein applied to the surface. Four proteins--fibronectin, collagen I/III, collagen IV/V, and laminin--were added and compared to saline pretreatment. The most significant variable affecting attachment was the time of incubation. When corrected for time, PET+ demonstrated significantly superior attachment kinetics when compared to PET- in most cases. These kinetics were similar to those seen on PS-. Fibronectin precoating of the surface greatly enhanced attachment kinetics on PET+ and PS- but to a much lesser degree on PET-. The fibronectin effect was synergistic with PDSM, suggesting that PDSM enhances protein adsorption on the surface. The force of attachment was generally independent of incubation time and surface/substrate combination except for laminin precoating. Taken together, these data indicate that human endothelial cell adherence to PET may be significantly enhanced by PDSM and surface precoating with fibronectin. Attachment occurs rapidly and, once attached, the cells demonstrate a very firm attachment force capable of resisting shear stresses up to 90 dynes/cm2.

Cell Adhesion↗
PubMed1989

Intravital fluorescence microscopy of endothelial cells on vascular grafts.

The ability to evaluate the extent of initial endothelial cell coverage on a vascular graft subsequent to an endothelial cell seeding technique would be desirable to substantiate the durability of the endothelial cell lining. To this end, we have evaluated the use of intravital fluorescence microscopy to assess human endothelial cell interaction with vascular grafts. Five fluorescent stains, mithramycin, Hoechst 33342, sulfofluorescein diacetate, Nile red, and rhodamine 123 were evaluated for their ability to fluorescently label human endothelial cells. The staining capability of each dye was also evaluated with respect to accuracy in determining seeded cell number and cell spreading. Of the stains evaluated, rhodamine 123 produced the most desirable characteristics. We observed excellent cell visualization after a 30-min incubation. Unlike the other four stains, rhodamine 123 exhibited a bright orange fluorescence emission at a 510-nm excitation wavelength while the underlying dacron or expanded polytetrafluoroethylene demonstrated minimal autofluorescence. Rhodamine 123 also exhibited no inhibitory effect on cell attachment to plastic or subsequent cell growth in culture. Intravital fluorescence microscopy could be easily utilized in the operating room to visualize part or all of an endothelial cell-seeded graft prior to implantation and would permit a quantitative as well as qualitative evaluation of the seeding process. Since intravital fluorescence imaging does not require tissue fixation, the same surface as that evaluated for seeding efficiency can be directly implanted.

Blood Vessels↗
PubMed1989

Effects of in vitro aging on human endothelial cell adherence to dacron vascular graft material.

The adherence and growth characteristics of cultured human adult large vessel endothelial cells (EC) maintained on substrate-coated polyethylene terephthalate in the form of woven dacron vascular graft were examined. Two different populations of EC, a low passage (EC (low] and a high passage (EC (high] population, were incubated at cell densities from 10(3) to 10(5) EC/cm2 for 24 hr. Cell counts were performed at 24 hr and after 14 days in tissue culture. At 24 hr on collagen I/III-coated Dacron, EC adherence was independent of the number of passages or the incubation density. When examined after 14 days in culture only EC (low) incubated at 10(5) EC/cm2 maintained initial cell numbers. Human plasma precipitated upon Dacron was necessary before significant cell growth occurred. We conclude that increasing in vitro EC age is associated with decreasing attachment and growth on Dacron. Growth on this important vascular replacement surface requires low passage EC incubated at a high density and the presence of plasma proteins in the substrate coating.

Blood Platelets↗
PubMed1989

Human microvessel endothelial cell isolation and vascular graft sodding in the operating room.

We have evaluated multiple factors inherent to an operating room-compatible endothelial cell procurement and sodding procedure. Microvessel endothelial cell isolations have been performed on fat tissue obtained from over 140 patients with a 100% success rate. Liposuction-derived fat was optimal with respect to cell yield, and isolation time. The devices and equipment used were acceptable to the operating room and the complete cell procurement procedure was successful even in the hands of personnel with minimal training. Fat digestion was achieved using crude clostridial collagenase, with an average cell yield of 1 x 10(6) microvessel endothelial cells/gm of fat. Evaluation of this procedure with canine fat using an operating room acceptable procedure resulted in a 100% procurement success rate requiring 1.5 hours (+/- .5 hrs) for completion of the fat isolation, and cell isolation procedure. Microvessel EC could subsequently be used in graft seeding or sodding techniques to establish endothelial cell monolayers on vascular grafts. Our results indicate that one person with minimal cell isolation background can reproducibly isolate large quantities of sterile autologous endothelial cells in the operating room for immediate use in endothelial cell seeding/sodding procedures.

Adipose Tissue↗
PubMed1989

Endothelial cell interactions with native surfaces.

Since native vessels are presumably the ideal surface for endothelial cells, we have examined endothelial cell interactions with natural surfaces as a standard to determine the possibilities obtainable on a surface. We have examined three separate types of natural surfaces including human amnion, superficially-injured human arteries, and tanned bovine carotid arteries. When basement membrane collagen is a principal component of a surface, such as with amnion or a superficially denuded large vessel, very rapid cell attachment and spreading occurs. Intact confluent monolayers covering 100% of the amnion surface are present as early as one hour. Human arteries superficially injured to denude their endothelium also exhibit excellent affinity for EC adherence and spreading. Endothelial monolayers cover 80.8% (+/- 5.3) of this surface after one hour, with 91.4% (+/- 1.2) coverage after two hours. For tanned bovine carotid arteries, one and two hour endothelial cell incubation results in coverage of 59.2% (+/- 1.3) and 75.9% (+/- 4.1), respectively. This surface is composed of interstitial collagen of the arterial wall in medial and adventitial layers. Electron microscopy reveals excellent endothelial cell spreading with little or no exposed underlying basement membrane. This suggests that polymeric surfaces designed to mimic injured native surface could allow an endothelialized surface to develop within minutes to hours.

Amnion↗
PubMed1989

Endothelialization of vascular prosthetic surfaces after seeding or sodding with human microvascular endothelial cells.

The rapid establishment of an endothelial cell (EC) monolayer on the luminal surface of small-diameter vascular grafts may be necessary to prevent early thrombosis and failure. We have studied procedures used to promote EC coverage of vascular grafts and have compared preclotting prosthetic surfaces with ECs in platelet-rich plasma (seeding) with plating ECs onto a preestablished clot (sodding). We evaluated the rate of monolayer formation, the subsequent resistance to shear stress, and the effects of EC growth factors (ECGF and heparin) on these functions. Woven Dacron was seeded or sodded at a density of 2 x 10(5) cells/cm2 with human adult microvessel ECs derived from adipose tissue. In the presence of ECGF-heparin, the immediate establishment of an EC layer after sodding was observed, whereas seeded grafts required almost 48 hours for cells to reach the surface. In the absence of ECGF-heparin, sodded grafts still exhibited a complete monolayer of EC, whereas ECs were not observed at the surface of seeded grafts after 48 hours. After exposure to shear stress (up to 20 dynes/cm2) for 2 hours, most freshly sodded EC remained attached; however, the loss of loosely adherent cells did occur. EC seeded grafts remained covered with fibrin matrix after exposure to shear stress. We conclude that the use of a microvessel sodding technique as an alternative to previously reported seeding techniques is necessary for the immediate formation of an EC monolayer before implantation.

Blood Vessel Prosthesis↗
PubMed1989

Pulmonary arterial hypertension: a contemporary review.

Pulmonary arterial hypertension has many causes, only some of which are well understood. The radiographic findings in pulmonary arterial hypertension are very similar regardless of the cause. Some radiographic features such as cardiac chamber enlargement, occur secondary to elevation of pulmonary pressures. In addition, sequential radiographs may demonstrate dramatic changes as the hypertension develops. This article presents examples of the various forms of pulmonary arterial hypertension, with pathologic correlation. Included are chronic pulmonary thromboembolism, plexogenic pulmonary arteriopathy, pulmonary venooclusive disease and persistent fetal circulation. Examples of lesions causing secondary pulmonary arterial hypertension: parenchymal lung disease, pulmonary venous hypertension, and congenital heart disease, are also illustrated.

Diagnostic Imaging↗
PubMed1988

Phenotypic diversity in cultured cerebral microvascular endothelial cells.

Diversity exists in both the structure and function of the endothelial cells (EC) that comprise the microvasculature of different organs. Studies of EC have been aided by our ability to first isolate and subsequently establish cultures from microvascularized tissue. After the isolation of microvessel endothelial cells (MEC) derived from rat cerebrum, we observed morphologic differences in colonies of cells that grew in primary cultures. The morphologies ranged from a cobblestone phenotype considered typical of EC in culture to elongated and stellate cell appearances. Serially passaged cell lines were established based on two parameters: initially by growth and, seconds, on differences in primary colony morphology using selective weeding techniques. Each culture was examined for the presence of EC-characteristic markers which include Factor-VIII-related antigen, angiotensin-I-converting enzyme activity, collagen type IV synthesis, and PGI2 production. Variable expression of each of these characteristics among the established EC lines was observed. Growth curves established for each of the EC cultures demonstrated differences in both population doubling rates and cell densities at confluence. The endocytic capacity of each EC line was also evaluated. Our ability to isolate and establish a number of morphologically distinct EC cultures indicates that diversity exists within the EC that comprise the cerebral microvasculature. Diversity in the established cell lines suggests either the EC that line the brain microvasculature exist as a mosaic or that morphologically distinct cultures may originate from different microanatomical origins (arteriolar, true capillary, or venular) or may have resulted from cells at different points in their in vitro life spans at the time of isolation.

Animals↗
PubMed1988

Permeability characteristics of cultured endothelial cell monolayers.

The purpose of this study was to characterize the permeability characteristics of an in vitro endothelial cell monolayer system and relate this information to available in vivo data. We cultured bovine fetal aortic endothelial cells on fibronectin-coated polycarbonate filters and confirmed that our system was similar to others in the literature with regard to morphological appearance, transendothelial electrical resistance, and the permeability coefficient for albumin. We then compared our system with in vivo endothelium by studying the movement of neutral and negatively charged radiolabeled dextran tracers across the monolayer and by using electron microscopy to follow the pathways taken by native ferritin. There were a number of differences. The permeability of our monolayer was 10-100 times greater than seen in intact endothelium, there was no evidence of "restricted" diffusion or charge selectivity, and ferritin was able to move freely into the subendothelial space. The reason for these differences appeared to be small (0.5-2.0 micron) gaps between 5 and 10% of the endothelial cells. Although the current use of cultured endothelial cells on porous supports may provide useful information about the interaction of macromolecules with the endothelium, there appear to be differences in the transendothelial permeability characteristics of these models and in vivo blood vessels.

Animals↗