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M Kadletz

Publications and source records attributed to M Kadletz.

29 records · Page 2Linked to original sources
PubMed1990

Mechanical simulation of shear stress on the walls of peripheral arteries.

In the last few years many attempts were made to line artificial vascular grafts with in vitro grown endothelial cell layers and thereby to minimize the risk of thromboembolism. However, adherence and resistance against shear stress forces were not tested under physiological pulsatile shear stress forces. In this paper, a mock-circulation apparatus is described, which simulates various forms of pulsatile shear stress, and which at the same time meets the requirements of cell cultivation. It can be sterilized and needs less than 700 ml of culture medium for priming. The generated flow profile can be adapted to a wide range of shear stress and also to different viscosities of used media. To take account of the different viscosities of culture medium and blood, a computerized calculation of the shear stress pattern was performed. Using the results of this computer model, the flow pattern was modified to obtain normal physiological shear stress when using culture medium. Results of pulse generation and simulation for the superficial femoral artery are presented.

Arteries↗
PubMed1990

[Experimental studies of extracellular matrix constituents for coating artificial prostheses before endothelialization].

Endothelialization seems to be a possibility to reduce thrombogenicity of artificial vascular prostheses. We have been occupied to find an ideal coating for the cells. Substances of extracellular matrix (ECM) were used: human fibronectin (HFN), laminin, collagen type I + III + IV. We have compared the influence of these materials with regard to adherence, sheer stress resistance and growth of cultivated human vena saphena endothelial cells (SEC). There was not any statistically significant difference according to cell proliferation. During a cultivation period of 7 days SEC increased by population doubling number 5 corresponding to a population doubling time of 76 hours. PTFE prostheses were coated with the materials, seeded with SEC and exposed to sheer stress in a physiological perfusion unit. Adherent SEC were counted after 24 hours of perfusion. Counts were correlated to the number of seeded cells. After perfusion only 23 +/- 4%, resp. 25 +/- 6% of cells were counted on collagen I + IV + HFN and on collagen I + IV + laminin. We found better results on collagen I + III and on collagen I + III + HFN; there were adherent 55 +/- 5%, resp. 53 +/- 7% after perfusion. These results document that there is no difference for SEC cultivation on different native components of basal membrane, under sheer stress conditions there seems to be differences in cell adherence.

Blood Vessel Prosthesis↗
PubMed1989

Use of fibrin glue as a substrate for in vitro endothelialization of PTFE vascular grafts.

The shear stress resistance of cultured human endothelium was investigated on 6 mm polytetrafluoroethylene vascular grafts. Endothelial cell attachment was promoted by precoating the grafts with fibrin glue, which contained human fibronectin and inhibitors of fibrinolysis (aprotinin and tranexam acid). To evaluate the possible effect of fibrinolysis on cell detachment, seven grafts were lined with adult human saphenous vein endothelial cells (AHSVEC) and 11 with fibrinolytically almost inactive human umbilical vein endothelial cells (HUVEC). Endothelial cell seeding was performed in a microprocessor-controlled rotation device, allowing a low inoculum of 12 X 10(4) endothelial cells/cm2. Grafts were then cultivated for 9 days to enable the maturation of the cytoskeleton, before they were exposed to pulsatile shear stress for 48 hours. A mock circulation simulated the flow patterns and the wall shear forces of the femoral artery. After a 3-hour seeding process, 45% of AHSVEC and 43% of HUVEC were attached to the fibrin matrix, forming a confluent monolayer. After 24 hours of perfusion, a cell loss of 23% in AHSVEC- and of 42% in HUVEC-lined grafts was encountered. In spite of a further cell loss during the following 24 hours of perfusion, the majority of the graft surface was still covered by endothelial cells. Therefore we conclude that fibrin glue is a suitable substrate for the formation of a shear stress-resistant endothelial cell monolayer on polytetrafluoroethylene vascular grafts.

Aprotinin↗
PubMed1989

Precoating substrate and surface configuration determine adherence and spreading of seeded endothelial cells on polytetrafluoroethylene grafts.

Primary adherence and attachment area of seeded human endothelial cells (EC) were determined on differently coated polytetrafluoroethylene (PTFE) grafts. Cell counts and morphometric analyses were done immediately after 60 minutes of electronically controlled seeding of 3 x 10(4) EC/cm2, as well as after 3 hours of subsequent incubation. Cell adherence and cell spreading were distinctly superior on two surface-covering substrates: fibronectin-treated type I/III collagen and fibrinolytically inhibited fibrin glue. Uncovered, purely fibronectin- or laminin-coated PTFE or type IV collagen treated with the specifically binding glycoprotein laminin showed a far lower EC attachment rate and less pronounced cell spreading. It appears that not only a high surface content of fibronectin but also a smooth PTFE-covering matrix are prerequisites for optimal primary adherence and cell spreading. Because fibrin glue might be fibrinolytically degraded despite its plasmin-inhibiting epsilon-amino-caproic acid compound, type I/III collagen plus fibronectin could provide an optimal precoating substrate for EC lining of PTFE grafts.

Aprotinin↗
PubMed1989

[Vascular replacement--a critical evaluation of status].

The beginning of angioplasty dates back to the turn of this century. Two lines of research were pursued over the past 40 years, organic and synthetic replacements of vessels. Autologous replacement, using an endogenous extremity vein, proved to be the most favourable variant. It was found to be not applicable to about 20 per cent of all patients, so that allogenic, semixenogenic or synthetic substitutes were required. Synthetic replacement was found to be characterised by a high rate of longtime closure, attributable to good biocompatibility of synthetic prostheses and low thrombogenic property of their inner surfaces. Endothelialisation of the prosthesis would be a possibility to improve the rate of success in bypass vascular surgery.

Arterial Occlusive Diseases↗
PubMed1987

In vitro lining of fibronectin coated PTFE grafts with cryopreserved saphenous vein endothelial cells.

In an attempt to produce instant endothelial cell (EC) monolayers on graft surfaces, cryopreserved cultivated human saphenous vein endothelial cells (HSVEC) were cultivated on reinforced PTFE prostheses. The graft surface was precoated with 40 micrograms/ml human fibronectin (HFN) prior to seeding with 200 x 10(3) EC/cm2. The seeding procedure was performed in a specially designed rotation device. After a cultivation period of 9 days, the seeded endothelial cells on the PTFE prostheses were exposed to shear stresses in a perfusion circuit, containing a bubble oxygenator, a roller pump and a tygon perfusion loop. The applied shear forces were 3 and 6 dyn/cm2, respectively. In control grafts, spontaneous cell detachment occurred from day 11 onwards and only 50% of the graft surface remained endothelialized on day 16. When the grafts were exposed to 3 dyn/cm2 only small cell-free areas less than 1000 micron in diameter were found after 4 hours of perfusion. In contrast, exposure to 6 dyn/cm2 produced discouraging results: as early as 4 hours after the onset of perfusion 50% of the graft surface was cell free. After 16 hours only 20% endothelial cell coverage was seen under the stereo microscope. However, assuming that an ideal precoating substratum can be found, the two stage technique of in vitro endothelialization of vascular grafts with autologous endothelial cells may offer a promising clinical method. Moreover, the fact that our grafts were lined with cryopreserved EC implies the possible prospect of cell banks supplying unlimited numbers of EC for subsequent bypass operations.

Blood Vessel Prosthesis↗
PubMed1987

Endothelial cell seeding of polytetrafluoroethylene vascular grafts in humans: a preliminary report.

The importance of initial human trials with autologous endothelial seeding lies not only in the implementation of a promising idea but also in the fact that canine data are only partially applicable to humans. The surface area of jugular veins in humans is much smaller than in dogs and considerably longer grafts are needed. Moreover, the reproductive capacity of adult human endothelial cells under in vivo conditions, which probably determines the success of seeding more than the seeding density, is also uncertain. Therefore the efficiency of autologous endothelial seeding in humans was investigated in 18 patients undergoing distal femoropopliteal bypass surgery. The average surface area of the jugular veins was 4.9 +/- 1.7 cm2 with an average cell yield of 32.6 +/- 18.0 x 10(4). The mean number of seeded cells per square centimeter of graft surface was 3.1 x 10(3). In a follow-up extending for 14 weeks, plasma levels of platelet factor 4 and beta-thromboglobulin as well as the platelet function in the whole blood aggregometer showed significantly better results in the seeded group. Plasma thromboxane B2, uptake and survival of indium 111-labeled platelets, and Doppler ultrasound investigations also favored the seeded group, but the results were statistically insignificant. No difference at all was found for the platelet dense granule compounds, releasable adenosine triphosphate and platelet serotonin. Thus our findings did not indicate the development of a closed endothelialized surface after 14 weeks, which is a period three times as long as the one required for confluent endothelial cell coverage in dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Scanning electron microscopy of circulating platelets reveals new aspects of platelet alteration during cardiopulmonary bypass operations.

Seventeen male patients undergoing cardiopulmonary bypass (CPBP) surgery for aorto-coronary bypass grafting were investigated by scanning electron microscopy (SEM) for alterations of the surface morphology of circulating platelets. An initial decline in the percentage of unactivated smooth discocytes (SD) to 87 +/- 12% was found after thoracotomy. Three minutes after the onset of CPBP, the percentage of SD had dropped drastically to 59 +/- 13%, and by the 8th minute of CPBP it had dropped to its lowest point (49 +/- 19%). On the other hand, the percentage of shape-changed platelets (SC) increased to 17 +/- 9% after 3 minutes, and the percentage of pseudopod discocytes (PD) to 25 +/- 13% after 8 minutes. Surprisingly, a remarkable recovery of platelet morphology could be observed after even 15 minutes of CPBP, and by the end of bypass 78 +/- 15% of the circulating platelets had regained the smooth discoid (SD) appearance of unactivated platelets. We conclude that this recovery of platelet morphology is due to an increasing insensitivity of the platelets to activating stimuli during the course of CPBP. Our study provides evidence that the only major platelet activation occurs during the first minutes of CPBP, and that CPBP-caused platelet activation is much less pronounced than generally believed.

Journal Article↗
PubMed1987

Endothelialization of artificial surfaces: does surface tension determine in vitro growth of human saphenous vein endothelial cells?

To evaluate the possibility of providing, in vitro, an endothelial lining for artificial hearts, we cultivated adult autologous endothelial cells on two polyurethane and two silicone rubber surfaces. Over the ensuing 11-day period, we investigated the resulting cell proliferation and morphology by means of scanning electron and light microscopy. On the silicone rubber surfaces, seeding of 200,000 human saphenous vein endothelial cells per cm(2) produced an ideal cobblestone monolayer within a single day. In contrast, the polyurethane surfaces displayed an uneven, patchy distribution of endothelial cells. Scanning electron microscopy revealed microvilli and marginal overlapping in both groups. After the first day, the cell count on the polyurethane surfaces increased, whereas the count on the silicone rubber surfaces decreased. Morphologic investigations revealed that the ideally shaped cells initially on the silicone rubber had begun to overspread and subsequently to become detached, leaving denuded spheroid areas. Moreover, cultivation for 11 days on the polyurethane surfaces resulted in an unevenness of cell distribution that far exceeded the unevenness seen on the first day. Thus, despite the fact that materials with a high surface tension (such as silicone rubbers) seem to be ideal for initial cell spreading, subsequent cultivation results in cell detachment and death. On materials with a lower surface tension (such as polyurethanes), the less differentiated monolayers do at least proliferate, although their morphology remains unsatisfactory. Even if adult human endothelial cells should prove shear-stress-resistant, a minimum of 6 to 8 weeks would be required to establish autologous endothelial cell monolayers on the inner surface. Therefore, the endothelialization of artificial hearts is not possible when such hearts are used for urgent "bridging" before cardiac transplantation.

Journal Article↗
PubMedDate not supplied

A model of BAX gene delivery to human lung cancer.

In this report we have investigated the effects of BAX in enhancing apoptosis in two primary non-small cell lung cancer cell lines. A count of the apoptotic cells by TUNEL staining revealed that almost 70% of BAX over-expressing cells died, while very few apoptotic cells were detectable in the wildtype cells or in the cells transfected with an empty vector. These findings suggest that de-regulated expression of BAX may provide a novel mechanism for initiating cell death in non-small cell lung cancer cells. Further studies are needed to better define the involvement of this protein in the complex mechanism of lung carcinogenesis and to definitely demonstrate the therapeutic utility of targeting this pathway.

Apoptosis↗