Polysaccharides as cell carriers for tissue engineering: the use of cellulose in vascular wall reconstruction.

Polysaccharides are long carbohydrate molecules of monosaccharide units joined together by glycosidic bonds. These biological polymers have emerged as promising materials for tissue engineering due to their biocompatibility, mostly good availability and tailorable properties. This complex group of biomolecules can be classified using several criteria, such as chemical composition (homo- and heteropolysaccharides), structure (linear and branched), function in the organism (structural, storage and secreted polysaccharides), or source (animals, plants, microorganisms). Polysaccharides most widely used in tissue engineering include starch, cellulose, chitosan, pectins, alginate, agar, dextran, pullulan, gellan, xanthan and glycosaminoglycans. Polysaccharides have been applied for engineering and regeneration of practically all tissues, though mostly at the experimental level. Polysaccharides have been tested for engineering of blood vessels, myocardium, heart valves, bone, articular and tracheal cartilage, intervertebral discs, menisci, skin, liver, skeletal muscle, neural tissue, urinary bladder, and also for encapsulation and delivery of pancreatic islets and ovarian follicles. For these purposes, polysaccharides have been applied in various forms, such as injectable hydrogels or porous and fibrous scaffolds, and often in combination with other natural or synthetic polymers or inorganic nanoparticles. The immune response evoked by polysaccharides is usually mild, and can be reduced by purifying the material or by choosing appropriate crosslinking agents.

A periadventitial sirolimus-releasing mesh decreased intimal hyperplasia in a rabbit model.

Autologous vein grafts used as aortocoronary bypasses are often prone to intimal hyperplasia, which results in stenosis and occlusion of the vein. The aim of this study was to prevent intimal hyperplasia using a newly developed perivascular system with sustained release of sirolimus. This system of controlled drug release consists of a polyester mesh coated with a copolymer of L-lactic acid and epsilon-caprolactone that releases sirolimus. The mesh is intended for wrapping around the vein graft during surgery. The mesh releasing sirolimus was implanted in periadventitial position onto arteria carotis communis of rabbits, and neointimal hyperplasia was then assessed. We found that implanted sirolimus-releasing meshes reduced intima thickness by 47+/-10 % compared to a vein graft after 3 weeks. The pure polyester mesh decreased vein intima thickness by 35+/-9 %. Thus, our periadventitial system for controlled release of sirolimus prevented the development of intimal hyperplasia in autologous vein grafts in vivo in rabbits. A perivascularly applied mesh releasing sirolimus is a promising device for preventing stenosis of autologous vein grafts.

The role of smooth muscle cells in vessel wall pathophysiology and reconstruction using bioactive synthetic polymers.

This review summarizes recent trends in the construction of bioartificial vascular replacements, i.e. hybrid grafts containing synthetic polymeric scaffolds and cells. In these advanced replacements, vascular smooth muscle cells (VSMC) should be considered as a physiological component, although it is known that activation of the migration and proliferation of VSMC plays an important role in the onset and development of vascular diseases, and also in restenosis of currently used vascular grafts. Therefore, in novel bioartificial vascular grafts, VSMCs should be kept in quiescent mature contractile phenotype. This can be achieved by (1) appropriate physical and chemical properties of the material, such as its chemical composition, polarity, wettability, surface roughness and topography, electrical charge and conductivity, functionalization with biomolecules and mechanical properties, (2) appropriate cell culture conditions, such as composition of cell culture media and dynamic load, namely cyclic strain, and (3) the presence of a confluent, mature, semipermeable, non-thrombogenic and non-immunogenic endothelial cell (EC) barrier, covering the luminal surface of the graft and separating the VSMCs from the blood. Both VSMCs and ECs can also be differentiated from stem and progenitor cells of various sources. In the case of degradable scaffolds, the material will gradually be removed by the cells and will be replaced by their own new extracellular matrix. Thus, the material component in advanced blood vessel substitutes acts as a temporary scaffold that promotes regeneration of the damaged vascular tissue.

Protein C and hypertension.

Protein C antigen and amidolytic activity were assayed in 38 patients with essential hypertension at the first stage of disease. As compared to 20 normal healthy blood donors no abnormality was found.

Clinical significance of protein C.

The coagulation inhibitors are important components of control mechanisms which ensure the haemocoagulation equilibrium. One of them is protein C, whose level was followed in patients with DIC. and IM. In DIC. cases a significant decrease was noted with regard to the MI groups and healthy donors. EID and ELISA methods were used for testing. The patients exhibiting the protein C defect require a corresponding treatment which should suppress the thromboembolic complications.

Platelet reactivity: a contribution to age dependence studies.

The authors examined 230 healthy donors (20-90 years) as to basic biochemical and haematological parameters and those parameters characterizing the function of blood platelets. Besides well known age dependences of fibrinogen concentration, AT III, erythrocyte sedimentation, glucose, cholesterol, alpha-2-macroglobulin and circulating immunocomplexes the results are presented showing a pronounced dependence of primary haemostatic system upon age. Within the age groups 65-75 years and those above 75 years there was a significantly higher amount of circulating aggregates (increase up to 152%), elevated concentration of beta-thromboglobulin and F VIII R:Ag. The increased reactivity of platelets is detectable even by applying relatively simple tests such as the determination of heparin-neutralizing activity, aggregation response to lower concentrations of induces or the determination of the amount of circulating aggregates.

Effect of lomustin on some platelet functions in vitro.

The effect of lomustin on platelet functions was investigated in vitro using a wide battery of tests. Lomustin was found to act as a specific inhibitor of platelet aggregation, release reaction and clot retraction and to induce acquired thrombocytopathy. Thus, impairment of platelet functions might play a role in hemorrhagic complications accompanying lomustin therapy in some cases.

Apolipoprotein B and platelet function in diabetes mellitus.

Serum levels of apolipoprotein B were measured, and investigations of the platelet function were carried out in 32 patients with insulin-dependent diabetes and in 34 healthy controls similar in age. Mean serum levels of apolipoprotein B were 1.51 g/l in the diabetic patients and 1.18 g/l in the control group, and this difference was significant. In the diabetic patients a secondary wave of aggregation was more easily induced by low concentrations of adenosine diphosphate or adrenaline. It was also possible to induce 50% of maximal aggregation by lower concentrations of adenosine diphosphate or arachidonic acid in these patients, and their number of circulating platelet aggregates increased. Plasma levels of beta-thromboglobulin and platelet factor 4 were raised and, in the presence of N-ethyl maleimide, platelets from diabetic patients produced significantly more malondialdehyde than those from normal controls. The relationship between increased serum levels of apolipoprotein B and platelet hyperreactivity may be more than accidental and should be studied further to elucidate its possible implication with platelet function and atherogenesis.

Relationship between platelet aggregation and plasma beta-thromboglobulin levels in arterio-vascular and renal diseases.

The incidence of second wave of platelet aggregation induced by a small dose of ADP (1 mumol/l) was compared with plasma levels of beta-thromboglobulin in 81 normal individuals, 34 patients with acute myocardial infarction, 11 patients with acute cerebrovascular disease and 26 patients with renal disease. Platelet hyperaggregability was observed in 7% of normal individuals. Plasma levels of beta-thromboglobulin were higher in normal individuals over 60 years of age (48 vs. 32 micrograms/l). In contrast, hyperaggregability was observed in 79% of patients with acute myocardial infarction and in 64% of those with acute cerebrovascular disease. Median plasma levels of beta-thromboglobulin were also significantly elevated in patients with acute myocardial infarction (82 micrograms/ml) or acute cerebrovascular disease (99 micrograms/l). Levels of beta-thromboglobulin in plasma were significantly higher in those patients who demonstrated hyperaggregability. In patients with renal disease only 12% had signs of hyperaggregability. Nevertheless their plasma levels of beta-thromboglobulin were elevated (76 micrograms/l) and correlated with the serum creatinine values. These investigations indicate that patients with acute myocardial infarction or stroke have hyperreactive platelets and evidence of increased platelet inactivation in the circulation. However, evaluation of increased levels of beta-thromboglobulin requires consideration of renal function.

Platelet function in hyperlipoproteinaemia.

A group of 53 healthy donors has been compared with another group of patients suffering from lipid metabolic disorders of Fredrickson type IIa (n = 14), IIb (n = 11) and IV (n = 21). In the course of three weeks the determinations have been carried out of lipid mechanism parameters, of Apoprotein B, of aggregation response upon ADP and adrenaline++ induction, of beta thromboglobulin, of heparin neutralizing activity, of malonyldialdehyde production upon N-ethylmaleimide stimulation and of the amount of circulating aggregates. In patients with HLP of IIa and IIb type a significant increase of plasmic beta thromboglobulin level was noted as well as shifts of other thrombocytic parameters towards higher platelet reactivity. The correlation between individual platelet parameters and parameters of lipid metabolism was statistically significant only in the case of cholesterol and malonyldialdehyde. A positive correlation of Apo B with BTG and with the aggregation response together with the observation of an increased Apo B concentration in normolipemic subjects with changed platelet reactivity, are indicative of an important role of Apo B during platelet activation in vivo.

Effect of cytostatics on some platelet functions in vitro. VI. Vinblastine.

The influence of vinblastine upon principal functions of blood platelets in vitro (adhesion, aggregation, platelet release reaction, membrane stabilization) has been followed using an extended system of laboratory examinations. The authors have found that the concentration of vinblastine which is higher than the average therapeutic dose (10(-5)M) inhibits the functional ability of platelets so that it may cause a thrombopatic disorder.

Influence of cytostatics on some platelet functions in vitro. V. Hydroxyurea.

Hydroxyurea added to citrated platelet-rich plasma in vitro did not influence the aggregation of the platelets, their adhesion to glass, their release of aggregating activity, platelet factor 4 or availability of platelet factor 3. Neither did it have any effect on the uptake of 14C-serotonin, the reptilase clot retraction or the coagulation system.