The Basement Membrane Underlying the Vascular Endothelium Is Not Thrombogenic: In Vivo and In Vitro Studies with Rabbit and Human Tissue

Improved endothelialization of titanium vascular implants by extracellular matrix secreted from endothelial cells

A variety of metals have been widely used in construction of cardiovascular implants (CVIs), such as artificial heart valves, ventricular pumps, and vascular stents. Although great effects have been put into rigorous anticoagulation, late thrombosis still occurred due to inferior blood and cell compatibility. Natural endothelium is popularly regarded as the only substance that has long-term anticoagulant ability. So, establishment of a compact endothelial cell (EC) monolayer on CVIs surface is a guarantee for their long-term potency. In the work described here, titanium (Ti) disks were coated with extracellular matrix (ECM) directly secreted by human umbilical vein endothelial cells (HUVECs), so as to help ECs proliferate and migrate and to improve their endothelialization in vivo. Deposition of ECM on Ti disks was detected by immunofluorescence microscopy, diffuse reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The surface topography and wettability of the Ti disks significantly changed after ECM deposition. Most importantly, it was found that ECM deposition inhibited platelet adhesion, stimulated EC proliferation, increased EC migration speed in vitro, and eventually accelerated the re-cellularization speed of Ti disks in vivo. These important results render it reasonable and feasible to modify CVIs with ECM secreted from ECs for improving their long-term potency.

Fogarty and percutaneous transluminal coronary angioplasty balloon injury induce comparable damage to the arterial wall but lead to different healing responses

PURPOSE

Fogarty balloon denudation in experimental animals often serves as a model for percutaneous transluminal coronary angioplasty (PTCA). We compared the healing response of the arterial wall with the use of Fogarty and PTCA balloon dilation.

METHODS

Carotid arteries of rabbits were injured with a 2F Fogarty (n = 9) or a 3 mm PTCA balloon (n = 6). At 1 day endothelial cell removal was qualitatively evaluated in Fogarty balloon lesions and in PTCA balloon lesions with a modified "en face" silver nitrate staining. Medial necrosis was morphometrically determined as percentage medial area. After 21 days endothelial cell coverage was assessed in the center of the lesion with an antibody to CD31 and intimal proliferation with an antibody to the nuclear antigen Ki-67. Intimal hyperplasia area was measured with morphometry. Acute lumen gain directly after Fogarty balloon dilation and PTCA balloon dilation was determined by serial angiography. All data are means +/- SEM.

RESULTS

At 21 days intimal hyperplasia area was higher in the Fogarty balloon lesions than in the PTCA balloon lesions. Intimal hyperplasia area was 0.19 +/- 0.02 mm2 and 0.03 +/- 0.01 mm2, respectively. Immediately after injury the acute gain in luminal diameter did not differ between Fogarty and PTCA balloon dilation (0.37 +/- 0.03 mm and 0.38 +/- 0.05 mm, respectively). At 1 day after injury endothelial cell removal was complete in all segments. Medial necrosis caused by Fogarty (67% +/- 7%) and PTCA balloon dilation (74% +/- 9%) did not differ. At 21 days endothelial cell coverage was almost complete both in the Fogarty balloon lesions and in the PTCA balloon lesions. Intimal proliferation was also higher in the Fogarty balloon lesions than in the PTCA balloon lesions.

CONCLUSION

Despite comparable endothelial cell abrasion and medial necrosis, Fogarty balloon injury elicited significantly augmented intimal hyperplasia compared with PTCA balloon dilation.

Involvement of von Willebrand factor and PGI2 in platelet binding to a partially denuded endothelial monolayer

Platelet binding to an endothelial monolayer was examined after denudation. The binding increased for up to 10 min and thereafter declined gradually. Antibodies against von Willebrand factor (vWF) inhibited the binding. Production of prostacyclin (PGI2) occurred 10 min after endothelial denudation. This study suggests that vWF is involved in the binding during the first 10 min and that PGI2 suppresses the binding thereafter.

Vein graft factors in the outcome of femorodistal bypass

Various vein factors affect the outcome of femorodistal bypass using vein in the treatment of lower limb ischaemia. In this review, the effect of factors such as vein size, compliance and morphology are discussed.

Changes in the microvasculature after mechanical pressure on the hamster cheek pouch

The reaction of the microvasculature in the periodontal ligament to mechanical pressure is considered a very important phenomenon with respect to the biological background to orthodontic tooth movement. For clarification of the microvascular reaction to mechanical pressure, an experimental model that incorporated a hamster cheek pouch was established. This in vivo model solves some of the problems of other experimental models of the microvasculature of the periodontal ligament. Blood plasma permeation in this model was examined by means of a blue dye (pontamine sky blue), and histological observation was performed by light and transmission electron microscopy. Increased vascular permeability was observed within 30 min after removal of the mechanical stimulation. The threshold weight resulting in dye leakage was between 1 and 5 g applied for 60 min. From the histological observations, some large gaps between the endothelial cells in venules were found, while most basement membranes remained undisturbed. These observations suggest that the plasma leakage was due to mild traumatic injury to the endothelial cells. Both leukocytes and platelets were observed in the gaps between the endothelial cells in the venule. These types of microvascular reactions to mechanical pressure could initiate tissue changes in the periodontal ligament during orthodontic tooth movement.

New artificial connective matrix-like structure: thrombogenicity and use as endothelial cell culture support

The recently described artificial connective matrix made of elastin solubilized peptides, type I+III collagens and connective proteins is shown to have structural and biological properties very close to the natural arterial subendothelium: the capacity to promote endothelial cell cultures maintaining their phenotype expression and its non-thrombogenicity. This new bioactive composite material could be used to replace arteries.

Eicosanoids, other fatty acid metabolites and the cardiovascular system: are the present antithrombotic approaches rational?

Antiplatelet +/- anticoagulant drugs are currently used as the standard treatment to prevent and treat thrombosis. While this approach is beneficial, it is not optimal. Recent evidence suggests that constituents of the vascular endothelium play an important role in regulating vessel wall thrombogenecity, thereby inhibiting thrombogenesis. These include constituents such as PGI2, tissue plasminogen activator, thrombomodulin and the lipoxygenase fatty acid metabolite derived from linoleic acid, 13-hydroxyoctadecadienoic acid (13-HODE). Consequently, new strategies have been developed to maximize the use of these agents for antithrombotic therapy. We will review these different approaches, discuss their rationale, and based upon recent experimental data, introduce an alternative approach for antithrombotic therapy which may circumvent a number of limitations and side-effect of the currently used drugs.

Effect of PGI2 on platelet binding to partially denuded endothelial monolayer in vitro

We have developed a new model for the investigation of platelet interaction with injured vascular endothelium. This involves the quantitative detection of platelet binding to a partially denuded endothelial cell monolayer in vitro. Porcine arterial endothelial monolayer, cultured on collagen gel containing fibrinogen and fibronectin, was partially denuded and the binding of 51Cr-platelets was measured. A synergistic increase in platelet binding was observed in the presence of fibrinogen and fibronectin. A distinct aggregation of platelets along the edge of the denuded area of the endothelial monolayer was seen. Prostacyclin (PGI2) inhibited platelet aggregation, although adhesive platelets were still present at denuded sites.

Percutaneous coronary and peripheral angioscopy with saline solution and carbon dioxide gas in porcine and canine arteries

To obtain a clear view with angioscopy, blood must be displaced. Carbon dioxide (CO2) gas has proved to be a safe intraarterial contrast agent, and it may have advantages over saline solution as an infusion medium for angioscopy. This study compared the use of CO2 gas and saline solution in the femoral artery, in the presence and absence of a proximal occlusion, in nine pigs and six dogs. The applicability of CO2 gas in the coronary arteries was also evaluated. In total 185 angioscopy procedures were evaluated. With proximal occlusion, angioscopy with CO2 gas was successful in all 28 peripheral procedures, whereas with saline solution only 65% of the procedures resulted in a clear view (p less than 0.005). Without proximal occlusion, angioscopy was successful with CO2 gas and saline solution in 61% and 3% of procedures, respectively (p less than 0.0001). Cardiovascular parameters and blood gases showed minor changes after administration of CO2 gas. During coronary angioscopy with CO2 gas, mechanical heart failure occurred in all instances, which was lethal in 12 animals. None of the animals died as a result of saline angioscopy. In conclusion, CO2 gas is a safe medium for angioscopy in the peripheral arteries and in general offers a better view than saline solution. In contrast to saline solution, without proximal balloon occlusion CO2 gas provided a clear view in 61% of the peripheral procedures. In the coronary arteries, however, CO2 angioscopy was generally fatal in both animal models.

Effect of 13-hydroxyoctadeca-9,11-dienoic acid (13-HODE) on thrombin induced platelet adherence to endothelial cells in vitro

The effect of exogenous 13-HODE on alpha-thrombin induced adherence of platelets to monolayers of cultured pulmonary artery endothelial cells was determined using homologous sheep cells. In a separate series of experiments, endogenous 13-HODE was demonstrated in sheep endothelial cells by reverse phase high pressure liquid chromatography. Levels of endogenous 13-HODE were decreased by alpha-thrombin preincubation. Exogenous 13-HODE (10 microM) reduced the augmented platelet adherence produced by coincubation of alpha-thrombin with platelets and endothelial monolayers, and eliminated the enhancement of platelet adherence produced by preincubation of alpha-thrombin with endothelial monolayers. 13-HODE also reduced the alpha-thrombin induced adherence of platelets to monolayers pretreated with aspirin and to fixed monolayers indicating a direct effect of 13-HODE as opposed to secondary effects mediated by the release of prostacyclin (PGI2) or endothelial derived relaxing factor (EDRF). Platelet adherence to subendothelial matrix was also reduced by 13-HODE. 13-HODE inhibited platelet aggregation initiated by 0.2 U/ml alpha-thrombin but did not affect aggregation initiated by 2.0 U/ml alpha-thrombin. These data provide evidence for the ability of exogenous 13-HODE to attenuate the interaction of thrombin activated platelets with endothelial cells as well as with other platelets.

Platelet adhesion to exposed endothelial cell extracellular matrixes is influenced by the method of preparation

The relative thrombogenicity of extracellular matrixes (ECMs) produced by cultured human umbilical endothelial cells (ECs) was studied under flow conditions. ECMs were prepared using a number of physical and chemical methods, and their reactivity toward platelets was morphometrically evaluated. von Willebrand factor (vWF), fibronectin (FN), and 13-hydroxy-9-cis,11-trans-octadecadienoic acid (13-HODE) were also determined. We found that platelet adhesion to ECMs differed significantly, both quantitatively and qualitatively, with the method of ECM preparation. Mechanically prepared ECM exposed a less thrombogenic surface compared with ECM prepared by chemical methods (platelet-covered surface of 20% and 50%, respectively). Evaluation of the ECM components vWF, FN, and 13-HODE showed significant changes, both in their concentrations and distribution patterns, depending on the method of ECM preparation. The decrease measured in the levels of ECM-associated vWF (from 108 to 9.2 ng/10(4) cells) and the minor changes observed in the distribution pattern of subendothelial FN did not appear to be sufficient to explain the altered platelet adhesion observed in our model. This suggests that the amount of 13-HODE probably associated to the remaining ECs present in the mechanically exposed ECM could be one factor that specifically contributed to the nonthrombogenic state of these preparations. We conclude that the degree of ECM reactivity toward platelets is dependent on the method of ECM preparation and that this is related to the removal of specific EC/ECM components that modulate their thromboresistant/thrombogenic properties. This fact should be taken into account when ECMs produced by cultured ECs are used in platelet adhesion studies.

Technical considerations in evaluating the endothelial integrity of rat aortic preparations with silver staining

Assessment of endothelial integrity is an obligatory step in many pharmacological studies. Integrity of endothelium is affected by manipulations performed during the removal and cleaning of the vessel and by some of the silver-staining techniques utilized for demonstrating interendothelial junctions. When aortas were cleaned of periadventitial tissue in cold Tris-saline (once separated from the animal) by untrained personnel, only 45% of the endothelium was preserved. When cleaning was performed in situ by trained personnel while flushing with cold Krebs-Ringer-6% albumin, over 95% was left intact. AgNO3-staining performed before fixation produced a 50% loss of endothelium when using NH4Br and (NH4)2S as developers. AgNO3-staining performed after fixation produced over 95% recuperation of endothelium when 2% glutaraldehyde, 150 mM NaCl, 40 mM phosphate buffer, pH 7.4, were utilized as initial fixative, NH4Br and (NH4)2S being equally effective as developers. Chloride ions were necessary to intensify silver lines. Several patterns of deendothelization were produced by mechanical and chemical injury with saponin, NH4Br and (NH4)2S. In all cases, hematoxylin staining was employed as an auxiliary technique to interpret images of injured endothelium. Presence of albumin protected the endothelium from mechanical damage.

Selective effects of dietary fats on vascular 13-HODE synthesis and platelet/vessel wall interactions

Fish oil (FO) diets are associated with decreased thrombosis, which is though to be related, in part, to changes in platelet and vessel wall prostanoid synthesis. Recently, we found that 13-hydroxyoctadecadienoic acid (13-HODE) synthesized in the vessel wall from linoleic acid (LA, 18:2 n-6) via the lipoxygenase pathway, also decreases platelet/vessel wall interactions. Thus, we determined whether diets containing fish oil, walnut oil (rich in linoleic acid), black currant seed oil (rich in both linoleic and gamma linolenic acids, 18:3 n-6), or lard influenced vessel wall 13-HODE synthesis and platelet/vessel wall adhesion in rabbits. In vivo, vessel wall thrombogenicity was decreased in animals fed the black currant seed oil rich diet for 4 weeks as compared to the control "LARD" diet. This latter effect was better obtained when gamma linoleic acid was present suggesting a secondary effect of this fatty acid. The decreased vessel wall thrombogenicity in those animals, was associated with increased vessel wall 13-HODE synthesis. In contrast, ex vivo platelet adhesivity was significantly decreased in the fish oil diet fed animals, as compared to the control "LARD" diet and correlated with decreased platelet 12-HETE synthesis. We conclude that both fish oil and black currant seed oil rich diets inhibit platelet/vessel wall adhesion; the black current seed oil diet by increasing the availability of linoleic acid for 13-HODE synthesis and inhibiting vessel wall thrombogenicity; the fish oil diet, by inhibiting platelet 12-HETE synthesis and subsequent platelet adhesion.

Relationship between vessel wall 13-HODE synthesis and vessel wall thrombogenicity following injury: influence of salicylate and dipyridamole treatment

We performed studies to determine the relationship between injured vessel wall thrombogenicity, vessel wall 13-hydroxyoctadecadienoic acid (13-HODE) synthesis and cAMP levels in rabbit treated with salicylate or dipyridamole. Injured vessel wall thrombogenicity was measured as the number of 3H-adenine labelled platelets adhered to the subendothelial basement membrane exposed by air injury in carotid arteries of rabbits treated orally with salicylate or dipyridamole. Vessel wall 13-HODE was measured by HPLC and vessel wall cAMP was measured by RIA. Vessel wall thrombogenicity was increased two-fold in rabbits treated with salicylate and decreased by half in rabbits treated with dipyridamole. The levels of vessel wall cAMP levels were correlated both with the plasma dipyridamole levels and increases in 13-HODE synthesis. cAMP levels were unaffected by salicylate treatment, but 13-HODE synthesis was decreased. We conclude that there is a significant relationship between vessel wall cAMP levels and 13-HODE synthesis, which in turn, influences subsequent vessel wall thrombogenicity.

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.

Endothelium and underlying membrane reactivity with platelets, leukocytes and tumor cells: regulation by the lipoxygenase-derived fatty acid metabolites, 13-HODE and HETES

We hypothesize that the ratio of intracellular 13-hydroxy-octadeca-dienoic acid (13 HODE) and hydroxy-eicosatetraenoic acid (5-, 12- and/or 15-HETE) influences the expression or presentation of adhesive moieties on platelets, leukocytes, malignant cells and endothelial cells, thereby influencing their subsequent adhesive interactions. Thus, we demonstrate that under unstimulated conditions, these cells preferentially synthesize linoleic acid via their lipoxygenase enzymes into 13-HODE, the intracellular level of which is associated with limited or no cell adhesion, while following stimulation, the same cells preferentially metabolize arachidonic acid via the lipoxygenase enzyme into HETEs, the production of which is associated with enhanced adhesion. Which metabolite is synthesized by these cells and the subsequent adhesivity of these cells appear to be dependent upon both the intracellular level of cAMP and the ratio of linoleic and arachidonic acid substrates. This suggests that manipulation of this ratio will have significant effects on the adhesive events involved in the pathogenesis of thrombosis, inflammation and metastasis.