Vessel injury, platelet adherence, and platelet survival

Cell Membrane-Based Biomimetic Nanoparticles and the Immune System: Immunomodulatory Interactions to Therapeutic Applications

Nanoparticle-based drug delivery systems have been synthesized from a wide array of materials. The therapeutic success of these platforms hinges upon their ability to favorably interact with the biological environment (both systemically and locally) and recognize the diseased target tissue. The immune system, composed of a highly coordinated organization of cells trained to recognize foreign bodies, represents a key mediator of these interactions. Although components of this system may act as a barrier to nanoparticle (NP) delivery, the immune system can also be exploited to target and trigger signaling cues that facilitate the therapeutic response stemming from systemic administration of NPs. The nano-bio interface represents the key facilitator of this communication exchange, where the surface properties of NPs govern their in vivo fate. Cell membrane-based biomimetic nanoparticles have emerged as one approach to achieve targeted drug delivery by actively engaging and communicating with the biological milieu. In this review, we will highlight the relationship between these biomimetic nanoparticles and the immune system, emphasizing the role of tuning the nano-bio interface in the immunomodulation of diseases. We will also discuss the therapeutic applications of this approach with biomimetic nanoparticles, focusing on specific diseases ranging from cancer to infectious diseases. Lastly, we will provide a critical evaluation on the current state of this field of cell membrane-based biomimetic nanoparticles and its future directions in immune-based therapy.

The Endothelial Cytoskeleton: Organization in Normal and Regenerating Endothelium*

The components of the endothelial cell cytoskeleton that have been shown to be important in maintaining endothelial structural integrity and in regulating endothelial repair include F-actin microfilament bundles, including stress fibers, and microtubules, and centrosomes. Endothelial cells contain peripheral and central actin microfilaments. The dense peripheral band (DPB) consists of peripheral actin microfilament bundles which are associated with vinculin adhesion plaques and are most prominent in low or no hemodynamic shear stress conditions. The central microfilaments are very prominent in areas of elevated hemodynamic shear stress. There is a redistribution of actin microfilaments characterized by a decrease of peripheral actin and an increase in central microfilaments under a variety of conditions, including exposure to thrombin, phorbol-esters, and hemodynamic shear stress. During reendothelialization, there is a sequential series of cytoskeletal changes. The DPB remains intact during the rapid lamellipodia mediated repair of very small wounds except at the base of the lamellipodia where it is splayed. The DPB is reduced or absent when cell locomotion occurs to repair a wound. In addition, when cell locomotion is required, the centrosome, in the presence of intact microtubules, redistributes to the front of the cell to establish cell polarity and acts as a modulator of the directionality of migration. This occurs prior to the loss of the DPB but does not occur in very small wounds that close without migration. Thus, the cytoskeleton is a dynamic intracellular system which regulates endothelial integrity and repair and is modulated by external stimuli that are present at the vessel wall-blood interface.

Deposition of fibrinogen on the surface of in vitro thrombi prevents platelet adhesion

The initial accumulation of platelets after vessel injury is followed by thrombin-mediated generation of fibrin which is deposited around the plug. While numerous in vitro studies have shown that fibrin is highly adhesive for platelets, the surface of experimental thrombi in vivo contains very few platelets suggesting the existence of natural anti-adhesive mechanisms protecting stabilized thrombi from platelet accumulation and continuous thrombus propagation. We previously showed that adsorption of fibrinogen on pure fibrin clots results in the formation of a nonadhesive matrix, highlighting a possible role of this process in surface-mediated control of thrombus growth. However, the deposition of fibrinogen on the surface of blood clots has not been examined. In this study, we investigated the presence of intact fibrinogen on the surface of fibrin-rich thrombi generated from flowing blood and determined whether deposited fibrinogen is nonadhesive for platelets. Stabilized fibrin-rich thrombi were generated using a flow chamber and the time that platelets spend on the surface of thrombi was determined by video recording. The presence of fibrinogen and fibrin on the surface of thrombi was analyzed by confocal microscopy using specific antibodies. Examination of the spatial distribution of two proteins revealed the presence of intact fibrinogen on the surface of stabilized thrombi. By manipulating the surface of thrombi to display either fibrin or intact fibrinogen, we found that platelets adhere to fibrin- but not to fibrinogen-coated thrombi. These results indicate that the fibrinogen matrix assembled on the outer layer of stabilized in vitro thrombi protects them from platelet adhesion.

Fibrinogen matrix deposited on the surface of biomaterials acts as a natural anti-adhesive coating

Adsorption of fibrinogen on the luminal surface of biomaterials is a critical early event during the interaction of blood with implanted vascular graft prostheses which determines their thrombogenicity. We have recently identified a nanoscale process by which fibrinogen modifies the adhesive properties of various surfaces for platelets and leukocytes. In particular, adsorption of fibrinogen at low density promotes cell adhesion while its adsorption at high density results in the formation of an extensible multilayer matrix, which dramatically reduces cell adhesion. It remains unknown whether deposition of fibrinogen on the surface of vascular graft materials produces this anti-adhesive effect. Using atomic force spectroscopy, single cell force spectroscopy, and standard adhesion assays with platelets and leukocytes, we have characterized the adhesive and physical properties of the contemporary biomaterials, before and after coating with fibrinogen. We found that uncoated PET, PTFE and ePTFE exhibited high adhesion forces developed between the AFM tip or cells and the surfaces. Adsorption of fibrinogen at the increasing concentrations progressively reduced adhesion forces, and at ≥2 μg/ml all surfaces were virtually nonadhesive. Standard adhesion assays performed with platelets and leukocytes confirmed this dependence. These results provide a better understanding of the molecular events underlying thrombogenicity of vascular grafts.

Differential Expression of Platelet Activation Markers CD62P and CD63 Following Stimulation with PAF, Arachidonic Acid and Collagen

The effects of varying concentrations of platelet-activating factor (PAF), arachidonic acid (AA) and collagen on the expression of the platelet activation markers CD63 and CD62P were assessed in 10 normal subjects using flow cytometry. CD63 expression was significantly greater than CD62P expression, with PAF (80 nM) inducing mean maximum CD63 expression of 32.9 ± 6.4% and mean maximum CD62P expression of 5.5 ± 1.8%. AA (1 mM) induced maximum CD63 expression of 37.7 ± 7% and maximum CD62P expression of 9.3 ± 1%. Collagen (2-80 pg/ml) induced minimal expression but 800 pg/ml induced mean CD63 expression of 33.1 ± 4.1% and mean CD62P expression of 6.1 ± 0.8%. Greater CD63 and CD62P expression were induced by phorbol myristate acetate (1.6 pM, 70.9 ± 11% and 69.4 ± 9.9%, respectively) and thrombin (0.1 U/ml, 70.7 ± 9.3% and 73.5 ± 5.4%, respectively). With PAF and collagen only one platelet population was detected whereas with 1 mM AA two populations were observed. These results indicate that expression of platelet adhesion receptors depends on the nature and concentration of agonist and that subpopulations of platelets may exist. Importantly, PAF concentrations inducing moderate CD63 and CD62P expression did not induce platelet aggregation, suggesting that platelets can be activated independently of aggregation.

Preoperative versus postoperative initiation of thromboprophylaxis following major orthopedic surgery: safety and efficacy of postoperative administration supported by recent trials of new oral anticoagulants

In European countries, low-molecular-weight heparin is generally initiated preoperatively for thromboprophylaxis in hip or knee replacement surgery. The objective of this review is to compare pre- and postoperative thromboprophylaxis strategies using available evidence, and discuss the challenges and issues that arise. Surgery is the first step in the process of thrombus formation, but thrombosis is not an instant process and the formation and growth of the thrombus can take several days or weeks. Hence, it may be possible to stop this process if thromboprophylaxis is initiated after surgery. Meta-analyses or systematic reviews comparing pre- and postoperative initiation of therapy have found no consistent differences in efficacy and similar safety (bleeding rates) between the two strategies. The recently available oral anticoagulant dabigatran etexilate provides thromboprophylaxis when administered postoperatively and is as safe as preoperative enoxaparin. Further support for the use of postoperative oral thromboprophylaxis in hip or knee replacement surgery has been provided by the phase III clinical trials of rivaroxaban and apixaban versus preoperative enoxaparin. Postoperative thromboprophylaxis offers the opportunity to change management practices in Europe. As postoperative initiation may have a clinical benefit in some settings (e.g. for neuraxial anesthesia) and practical advantages (e.g. allowing same-day admission), it is a worthwhile thromboprophylactic strategy for hip or knee replacement surgery.

Venous thrombosis in patients with short- and long-term central venous catheter-associated Staphylococcus aureus bacteremia

OBJECTIVE

Infection and thrombosis are important complications of intravascular catheters. The purpose of this study was to determine the incidence of thrombosis in patients with central venous catheter-associated Staphylococcus aureus bacteremia and the utility of physical examination for diagnosing upper extremity or neck venous thrombosis.

DESIGN

Prospective observational cohort.

SETTING

Tertiary care facility.

PATIENTS

In all, 65 consecutive patients with catheter-associated S. aureus bacteremia with central venous catheters of the internal jugular, brachial, or subclavian veins were eligible for participation.

INTERVENTION

From July 1999 through August 2004, enrolled patients underwent physical examination and ultrasonography independently to identify the presence of catheter-associated thrombosis. Study ultrasonograms were interpreted blindly using defined criteria. Outcomes were defined at 12-wk follow-up.

MEASUREMENTS AND MAIN RESULTS

A total of 48 patients were enrolled. By ultrasonography, definite or possible thrombosis was present in 34 of 48 patients (71%) in this cohort. Death or recurrent bacteremia occurred in 11/34 (32%) infected patients with thrombosis and two of 14 (14%) infected patients without thrombosis (p = .29). Sensitivity of all physical examination findings, either alone or in combination, was low (< or = 24%). Only engorged veins upon hand elevation and the presence of multiple physical examination abnormalities were specific (100% each).

CONCLUSIONS

Thrombosis is a common complication of central venous catheter-associated S. aureus bacteremia. Patients with central venous catheter-associated S. aureus bacteremia should undergo ultrasonography to detect thromboses even if the physical examination is normal.

Procoagulant surface exposure and apoptosis in rabbit platelets: association with shortened survival and steady-state senescence

BACKGROUND

The signal(s) for removal of senescent platelets from the circulation are not fully understood; phosphatidylserine (PS) expression on platelets and another marker of apoptosis, loss of mitochondrial inner membrane potential (DeltaPsim), have been implicated in platelet clearance.

OBJECTIVE

To investigate whether shortened platelet survival and steady-state platelet senescence are associated with increased surface exposure of PS and DeltaPsim collapse.

METHODS

Survival of in-vitro biotinylated rabbit platelets treated with thrombin or Ca(2+)-ionophore A23187 was tracked by flow cytometry after injection. Steady-state platelet senescence was investigated by infusing biotin to label a platelet cohort. PS expression and DeltaPsim of in-vitro biotinylated platelets and of the aging platelet cohort biotinylated in-vivo were measured by flow cytometry using annexin V-FLUOS and the DeltaPsim-sensitive dye CMXRos, respectively.

RESULTS

Although PS expression, DeltaPsim and survival of thrombin-degranulated platelets were similar to those of control platelets, increasing concentrations of A23187 caused increased surface exposure of PS and progressive shortening of platelet survival; only one-sixth of PS-expressing platelets also exhibited DeltaPsim loss. The cohort of senescent, biotinylated platelets remaining in the circulation at 96 h had increased exposure of PS and collapsed DeltaPsim; of the 17% of PS-expressing platelets, one-third did not exhibit DeltaPsim loss. There was also an increase in platelets with collapsed DeltaPsim but not expressing PS.

CONCLUSIONS

Platelets with shortened survival and senescent platelets have increased surface exposure of PS, that may be involved in their clearance. PS expression can occur independently of DeltaPsim collapse and conversely, in aged platelets, DeltaPsim loss can occur independently of PS expression.

Concurrent measurement of the survival of two populations of rabbit platelets labeled with either two PKH lipophilic dyes or two concentrations of biotin

BACKGROUND

To avoid radioisotopic labeling and permit comparison of the survival of two platelet populations concurrently in one animal, we compared simultaneous recoveries and survival times of homologous rabbit platelets labeled in vitro with the lipophilic dyes PKH26 (red fluorescing) and PKH67 (green fluorescing) and with two levels of biotin (low, 1 microg/ml; high, 10 microg/ml).

METHODS

Blood samples were drawn up to 96 h postinfusion and analyzed by flow cytometry. Biotin-labeled samples were incubated with phycoerythrin-streptavidin before analysis.

RESULTS

Recovery of PKH26-labeled platelets at 1 h was lower (37.5%) than that of PKH67-labeled platelets (47.3%; P < 0.001). Platelet survival times were 62.4 and 61.9 h. Recoveries at 1 h of platelets labeled with two levels of biotin were similar (86.6% and 84.6%) and greater than those of PKH-labeled platelets (P < 0.001). Survival of platelets labeled with biotin did not differ (low, 83.3 h; high, 85.2 h) and was longer than for PKH-labeled platelets (P < 0.01). Labeling methods did not activate platelets (measured by P-selectin expression), nor did they affect platelet responses to adenosine diphosphate (ADP), collagen, or thrombin.

CONCLUSIONS

Labeling with two levels of biotin is superior to labeling with PKH dyes, and is useful for measuring concurrently the survival of two differing platelet populations.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

Continuous infusion of prostacyclin normalizes plasma markers of endothelial cell injury and platelet aggregation in primary pulmonary hypertension

BACKGROUND

Primary pulmonary hypertension (PPH) is characterized by vascular injury of pulmonary arterioles, in which endothelial dysfunction may play a major role. Although continuous infusion of prostacyclin (prostaglandin I2, a potent vasodilator released by vascular endothelial cells) improves the clinical status and survival in PPH, its mechanism or mechanisms of action remain unclear.

METHODS AND RESULTS

We measured endothelium-derived clotting factors and assayed platelet aggregation in 64 patients (26 adults and 38 children) with PPH before long-term PGI2 therapy. Repeat studies were performed in 42 patients (18 adults, 24 children) after one year of PGI2 therapy. At baseline, 87% of adults and 79% of children had abnormal platelet aggregation. In addition, factor VIII, von Willebrand (vW) antigen, and ristocetin cofactor levels were abnormally high in 92%, 72%, and 52%, respectively, of the adults versus 29%, 16%, and 16%, respectively, of the children (P<.005 adults versus children). With long-term PGI2, platelet aggregation normalized in 83% of the adults and 80% of the children who had platelet aggregation abnormalities at baseline (P<.01). Factor VIII, vW antigen, and ristocetin cofactor also decreased with long-term PGI2 in both groups (P<.02). The ratio of ristocetin cofactor to vW antigen, which may reflect biological activity of vW factor, increased with long-term PGI2 in adults from an abnormally low level (0.6+/-0.2) to normal level (1.10+/-0.4), and in children the ratio increased from 0.8+/-0.3 to 1.3+/-0.4 (normal, 0.8 to 1.4).

CONCLUSIONS

Alterations in the coagulation system may contribute to the pathogenesis of PPH; the normalization of these endothelial markers concomitant with improvement in hemodynamic parameters with long-term PGI2 suggests that long-term PGI2 remodels the pulmonary vascular bed with subsequent decreases in endothelial cell injury and hypercoagulability.

Collagen-induced thrombus formation in flowing nonanticoagulated human blood from habitual smokers and nonsmoking patients with severe peripheral atherosclerotic disease

The objective of the present study was to investigate collagen-induced platelet thrombus formation at arterial blood flow conditions in nonanticoagulated blood from habitual smokers and from nonsmoking patients with severe peripheral atherosclerotic disease. Collagen-induced thrombogenesis was elicited in native blood drawn directly from an antecubital vein over immobilized type III collagen fibrils coated on a coverslip positioned in a parallel-plate perfusion chamber. The wall shear rates at the collagen surface were comparable to those encountered in medium-sized (650 s-1) and moderately stenosed (2600 s-1) arteries. Thrombus formation in blood from habitual smokers after 10 hours of smoking abstinence appeared to be not different from thrombus formation in blood from healthy nonsmokers. However, immediately after a cigarette had been smoked, thrombus volume in blood from the same individuals was increased twofold at the highest shear rate (P < .05). Thus, the thrombotic response was temporarily upregulated after smoking. Thrombus formation in blood from nonsmoking patients with severe peripheral atherosclerotic disease was neither enhanced nor decreased but was within the range of the nonsmoking control subjects. However, fibrinopeptide A generation after 4 minutes of perfusion at 2600 s-1 was higher in blood from the atherosclerotic patients (P < .05) and associated with a higher plasma fibrinogen level (P < .005). Thus, signs of changed platelet reactivity in flowing nonanticoagulated blood were encountered only in the habitual smokers immediately after they had smoked a cigarette.

Platelet calcium homeostasis is abnormal in patients with severe arteriosclerosis

To evaluate platelet calcium homeostasis in a typical thrombosis-prone clinical condition, 14 patients with severe arteriosclerosis and 11 healthy control subjects were studied. Platelet intracellular free calcium concentration ([Ca2+]i) was evaluated by means of the fluorescent probe fura 2 under resting conditions and after challenge with 0.05, 0.1, and 0.5 U/mL thrombin (final concentrations). Three different concentrations of extracellular ionized calcium ([Ca2+]e) were used: 1 mmol/L, 1 mumol/L, and < 1 nmol/L. Resting platelet [Ca2+]i was significantly higher (P < .001) in patients than in control subjects. After addition of 0.05 U/mL thrombin, the relative increase of [Ca2+]i was lower in patients than in control subjects in each of the three [Ca2+]e conditions (P = .05 at 1 mmol/L, P = .02 at 1 mumol/L, and P = .04 at < 1 nmol/L). After addition of 0.1 U/mL thrombin, the relative increase of [Ca2+]i was lower in patients than in control subjects under two [Ca2+]e conditions, 1 mumol/L and < 1 nmol/L (P = .04 and P = .03 respectively). With 0.5 U/mL thrombin, a trend toward lower values in patients than in control subjects was observed, reaching statistical significance (P = .03) only at < 1 nmol/L [Ca2+]e. These results suggest that calcium homeostasis is abnormal in platelets from patients with severe arteriosclerosis and probably reflects a chronic activation.

Absence of ligands bound to glycoprotein IIB-IIIA on the exposed surface of a thrombus may limit thrombus growth in flowing blood

We examined the distribution of glycoprotein IIb-IIIa (GPIIb-IIIa) and its ligands fibrinogen and von Willebrand factor (vWf) on platelets which had adhered under flow conditions. Immunoelectron microscopy was performed on whole mounts and frozen thin sections of adhering platelets. GPIIb-IIIa was homogeneously distributed on dendritic platelets and on interplatelet membranes of formed thrombi. Fibrinogen and vWf were predominantly associated with interplatelet membranes and membranes facing the substrate. On whole mounts, vWf appeared in clumps and linear arrays, representing the tangled or extended forms of the multimeric molecule. From semiquantitative analysis, it appeared that fibrinogen and vWf were, respectively, nine- and fourfold higher on interplatelet membranes than on surface membranes facing the blood stream, while GPIIb-IIIa was evenly distributed over all platelet plasma membranes. Ligand-induced binding sites (LIBS) of GPIIb-IIIa, as measured with conformation specific monoclonal antibodies RUU 2.41 and LIBS-1, were present on the surface of adhered platelets and thrombi. A redistribution of LIBS-positive forms of GPIIb-IIIa towards interplatelet membranes was not observed. Our data support the hypothesis that, under flow conditions, ligands have first bound to activated GPIIb-IIIa but this binding is reversed on the upper surface of adhering platelets. This relative absence of ligands on the exposed surface of thrombi may play a role in limiting their size.

Increased urinary excretion of a major thromboxane metabolite in early alcohol withdrawal

Urinary excretion of 2,3-dinor-thromboxane B2 as a marker of in vivo thromboxane A2 (TxA2) biosynthesis was measured in six alcoholics 1 and 14 days after the cessation of heavy drinking using gas chromatography/mass spectrometry. Six non-alcoholic healthy volunteers served as controls. One day after alcohol withdrawal the excretion of the dinor metabolite was significantly higher (P < 0.01) in the alcoholics (408 +/- 42 pg mg-1 creatinine) than in the controls (180 +/- 30 pg mg-1 creatinine) and was accompanied by a significantly reduced platelet count (103.0 +/- 20.2 x 10(9) l-1 vs. 194.0 +/- 13.9 x 10(9) l-1 in controls; P < 0.01). The metabolite excretion fell then significantly (P < 0.05) to 245 +/- 53 pg mg-1 creatinine 14 days after alcohol withdrawal and this was paralleled by an increase in platelet count to 453.5 +/- 72.0 x 10(9) l-1 (P < 0.05). The present results support the hypothesis that Tx-A2 biosynthesis is increased in early alcohol withdrawal and strongly suggest platelets as a cellular origin of the increased TxA2 formation.

Role of platelets and leukocytes in modulation of vascular tone

Activated platelets and leukocytes release potent vasoactive factors that may modulate vascular tone. Activation of normal platelets produces dilatation of normal arteries. Vasodilatation is mediated by adenosine diphosphate (ADP), which releases endothelium-derived relaxing factor (EDRF) from endothelium. In atherosclerotic arteries, activation of platelets produces constriction and perhaps spasm. The constrictor response of atherosclerotic arteries is related in part to profound changes in vascular function: endothelial dysfunction with impaired endothelium-dependent vasodilator responses to ADP, and augmented vasoconstrictor responses to serotonin. In addition, hypercholesterolemia has a direct effect on platelets, resulting in impaired vasodilator responses. Thus, abnormal platelets and altered vascular function may both predispose to spasm of atherosclerotic arteries. Activation of leukocytes has little effect on resistance of large arteries in normal monkeys. In contrast, activation of leukocytes produces pronounced vasoconstriction in atherosclerotic monkeys. Possible mediators of vasoconstriction include prostaglandin E2, oxygen radicals, thromboxane, and a peptide (perhaps angiotensin II). In addition, leukocytes also alter vascular responses to platelets, in part by ADPase on the leukocyte membrane, which degrades ADP released by activated platelets. Leukocytes also release oxygen radicals, which may inactivate EDRF, thereby impairing ADP-mediated, endothelium-dependent vasodilator responses. Abnormal responses to platelets and leukocytes are largely reversed when atherosclerotic lesions regress in monkeys.

Endothelial cell seeding of damaged native vascular surfaces: prostacyclin production

Endothelial cell seeding has been successful in reducing the thrombogenicity of prosthetic vascular grafts in animal and clinical studies. The reduction in thrombogenicity may be attributed to the intrinsic properties of endothelial cells themselves, and their ability to produce anti-thrombogenic mediators such as prostacyclin, and endothelium-derived relaxing factor. Endothelial seeding of damaged vascular surfaces produced during percutaneous transluminal angioplasty and endarterectomy is an attractive possibility due to the excellent attachment characteristics of the sub-endothelial tissue exposed during these procedures. The ability of endothelial seeded damaged vascular surfaces to produce prostacyclin was measured in an in vitro model of vascular injury. Endothelial-seeded damaged surfaces produced significantly higher prostacyclin release than did vessels damaged by balloon dilatation (265.5 pg cm-2 min-1 and 87.5 pg cm-2 min-1 respectively). This study provides evidence that endothelial seeding of damaged native vascular surfaces is technically feasible and that seeding may reduce the thrombogenicity of vascular surfaces following balloon dilatation.

Platelet adherence and detachment with adsorbed fibrinogen: a flow study with a series of hydroxyethyl methacrylate-ethyl methacrylate copolymers using video microscopy

The adhesion and detachment of platelets were studied on glass coatings of a series of copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) with preadsorbed fibrinogen. Observations of the interactions of acridine-orange-labeled washed platelets with these surfaces from a flowing (500 s-1 wall shear rate) suspension in Tyrode's solution containing albumin and red cells were made with epifluorescent video microscopy (EVM). In some cases preadsorbed materials were incubated for 24 h, during which little or no loss of protein occurred. Protein surface concentration, by itself, was a poor indicator of expected cell adhesion and morphology. Surface chemistry was a second important factor which must be considered. A third observation is that for the 100% EMA copolymer, 24 h of incubation led to a large reduction in platelet adhesion when compared to the 100% EMA material without incubation. For the 0% and 100% EMA polymers, the percentage of contacting platelets which adhere and detach is greater for the 24-h incubation cases than for those not incubated. These results led to the conclusion that our most hydrophilic surface favors adhesion with detachment, transient cell contact, over long-term adhesion, as does incubation of adsorbed protein. A brief discussion is presented of a possible connection between this behavior and platelet consumption in vivo for hydrogels.

Arterial response to mechanical injury: balloon catheter de-endothelialization

Coronary angioplasty has been used clinically for over a decade. Its initial promise as an alternative to coronary bypass surgery has only partially been fulfilled because of the high rate of post-operative restenosis. A number of animal models have been devised to study this phenomenon and although none is entirely satisfactory, they have, together with recent advances in molecular biology provided an insight into the cellular mechanisms that may contribute to this complication. This knowledge may ultimately lead to a means of therapeutic intervention. This review summarises our present understanding of the pathology of post-angioplasty re-stenosis as revealed by studies using the balloon catheter de-endothelialization model, and discusses some of the intervention strategies that have been attempted.

Vascular responses to platelet activation in normal and atherosclerotic primates in vivo

Platelets release vasoactive substances that may contribute to augmented vasoconstriction. In this study, we examined vascular responses to activation of platelets in vivo by infusion of collagen. Purified bovine collagen was infused into the blood-perfused hind limb of normal and atherosclerotic cynomolgus monkeys. Resistance of the total limb and large arteries was measured at constant flow. In normal monkeys, collagen produced a decrease in total limb resistance, with a modest constrictor response of the large arteries. In atherosclerotic monkeys, collagen produced a transient, small decrease in total limb resistance, with pronounced constriction of large arteries. Indomethacin (5 mg/kg i.v.) and the thromboxane A2/prostaglandin H2 receptor antagonist SQ29,548 (2 mg/kg i.v.) virtually abolished the large-artery constrictor response to collagen in atherosclerotic monkeys. The 5-HT2-serotonergic receptor antagonist ketanserin (0.6 mg/kg i.v.) had no effect on the vasoconstrictor response. We conclude that 1) large arteries constrict and small vessels dilate in response to collagen-mediated activation of platelets in vivo in normal and atherosclerotic monkeys, 2) large-artery constriction in response to activation of platelets is augmented in atherosclerotic monkeys, and 3) the augmented large-artery constriction in atherosclerotic monkeys may be mediated primarily by thromboxane. The findings provide evidence that platelets may contribute to augmented constrictor responses of atherosclerotic arteries.

The peripheral vascular consequences of smoking

Cigarette smoking is associated with an increased risk and extent of advanced atherosclerotic vascular disease in peripheral as well as coronary arteries. The likelihood of claudication, amputation, stroke, abdominal aortic aneurysm, and failure of vascular reconstruction is higher in smokers than nonsmokers. Smoking exerts its deleterious effects through many interactive mechanisms. Nicotine and carbon monoxide produce acute cardiovascular consequences, including altered myocardial performance, tachycardia, hypertension, and vasoconstriction. Smoking injures blood vessel walls by damaging endothelial cells, thus increasing permeability to lipids and other blood components. Among metabolic and biochemical changes induced by smoking are elevated plasma, free fatty acids, elevated vasopressin, and a thrombogenic balance of prostacyclin and thromboxane A2. Chronic smoking is associated with a tendency for increased serum cholesterol, reduced high density lipoprotein, and other lipid effects that contribute to atherosclerosis. In addition to rheologic and hematologic changes from increased erythrocytes, leukocytes, and fibrinogen, smokers have alterations in platelet aggregation and survival that produce thrombosis. Considering the ubiquitous repercussions of this menace, vascular surgeons should play an active role in motivating their patients to quit smoking.

Myointimal hyperplasia: pathogenesis and implications. 2. Animal injury models and mechanical factors

Arterial wall injury either by balloon catheter, drying, or scraping results in a denudation of endothelial cells (EC) and a subsequent proliferation of smooth-muscle cells (SMC). The degree of SMC proliferation appears to be dependent on the degree of initial injury and not to the loss of the overlying endothelium. Successful reendothelialization of denuded areas depends on the size of the denuded segment as well as SMC-EC interactions. Prolonged exposure of SMC to serum substances results in inhibition of EC regrowth, the production of prostacyclin by SMC, and the development of a thromboresistant surface. Heparin appears to inhibit SMC proliferation in vivo (as well as in vitro), an effect that is independent of platelet SMC interaction. EC-derived heparin in vivo may also result in inhibition of SMC proliferation. Platelets may play an important role in the early response to arterial injury and development of myointimal hyperplasia (MIH), but their long-term role appears to be minor. Antiplatelet agents have widely varying species-dependent effects on platelets and platelet-vessel wall interactions, but in specific circumstances they may inhibit MIH. The precise role of steroid drugs and immunosuppression on MIH in arterial injury models awaits further study. The role of lipoproteins in MIH is unclear; however, the inhibition of MIH by omega-3 fatty acids in vivo as well as their inhibition of platelet-derived growth factor production by EC in vitro implies a regulatory role. Acute hypertension results in a marked proliferation of EC and SMC in vivo and enhances the proliferative response to injury as well. Low wall shear stress, turbulence, and boundary layer separation all increase EC turnover, a likely influence on EC growth factor production. The compliance mismatch resulting from graft-artery anastomoses, injury, and endarterectomy results in locally increased cyclical stretch, which may predispose to SMC proliferation.

Platelet adherence and detachment: a flow study with a series of hydroxyethyl methacrylate-ethyl methacrylate copolymers using video microscopy

The adhesion and detachment of platelets were studied on glass coatings of a series of copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA). Observations of the interactions of mepacrine labelled washed platelets with these surfaces from a flowing (500 s-1 wall shear rate) suspension in Tyrode's solution containing albumin and red cells were made with epifluorescent video microscopy (EVM). Total platelet adhesion, including platelets which adhere on first contact and platelets which attach temporarily before adhesion, and the number of detaching platelets were minimal for the 0 and 20% EMA copolymers, reached a maximum for the 50% EMA copolymer and showed reduced values for the 80% and 100% EMA copolymers. For the 50, 80, and 100% EMA copolymers, the adhesion values expressed, as a percentage of total contacting platelets, were not different. Albumin adsorption to these copolymers shows a continuous increase from the 0% to the 100% EMA copolymer. It is likely that the peak in platelet adhesion at the 50% EMA composition is related to: low protein adsorption on the 0 and 20% EMA copolymers, too little albumin adsorption to block adhesion on the 50% EMA copolymer, and full-scale blocking on the 80 and 100% EMA copolymers due to greater albumin adsorption.

The relation among vessel injury, thrombus formation, and platelet survival in rabbits

Continuous or repeated injury of rabbit aortae by indwelling vascular catheters caused the deposition of platelets on the injured vessels and the formation of thrombi rich in platelets and fibrin at sites where flow was most disturbed and injury was most extensive. Incorporation of 51Cr platelets into the thrombi reached a maximum between 3 and 24 hr. The platelet-fibrin-rich thrombi remained reactive to circulating platelets for at least 14 days. Continuing reactivity of thrombi and the turnover of platelets in the thrombi were accompanied by an increase in the proportion of platelets that separated in the least dense fraction on Stractan density gradients. Platelet survival was also shortened (43.5 +/- 5.9 hr in animals with catheters, compared with 62.6 +/- 4.5 hr in animals with a sham operation), indicating that some platelets that had taken part in thrombus formation or had interacted with the injured vessel wall were rapidly cleared from the circulation. Platelets from rabbits that had had indwelling aortic catheters in place for 3 or 6 days survived significantly longer than those from animals with a sham operation upon injection of the platelets into normal animals; thus, continuous turnover of platelets on injured vessels and thrombi, and the clearance of altered platelets, leads to a population of younger platelets that survive longer. The continuing reactivity of thrombi may in part account for repeated occlusive episodes in vascular disease. The contribution of thrombin generation and fibrin formation to the platelet-rich thrombi is substantial and warrants the ongoing evaluation of treatment with a combination of anticoagulant and antiplatelet agents in arterial thrombosis and in thrombus formation on vascular catheters.

Survival of rabbit platelets exposed to immune complexes

Rabbits injected with human serum albumin (HSA) formed detectable immune complexes after 5 days; complex formation was maximal between 11 and 14 days after which the complexes were cleared from the circulation. Platelets from control rabbits or HSA-injected rabbits had a reduced survival upon injection into rabbits in which complexes were forming. Platelets from HSA-animals tended to survive for a longer period upon injection into control rabbits than when they were injected into HSA-rabbits, raising the possibility that some of the immune complexes may have eluted from their surface. Platelets prepared from either control animals or from HSA-treated animals at the time when complexes were being cleared from the circulation (14-21 days) did not have a shortened life span in HSA- or control rabbits. When platelet survival was reduced, it could not be attributed to platelet accumulation at sites of vessel wall injury or to accumulation in kidneys damaged by immune complexes, since the tissues (aorta and kidney) appeared to be morphologically normal and free of thrombi. The reduction in platelet survival likely results from the interactions of immune complexes with the surface of platelets leading to the platelets being recognized as "foreign" and cleared from the circulation by the reticuloendothelial system.

Platelet-vessel wall interactions in individuals who smoke cigarettes

Our studies have shown that there an increased excretion of urinary metabolites of thromboxane A2 in healthy, young male chronic smokers. This arachidonic acid metabolite from platelets reflects evidence of increased activation in vivo. These data contrast with the ex vivo study of platelets in chronic smokers and point out the fact that selection of cells for ex vivo study may not appropriately reflect the in vivo pathophysiologic situation. The platelet activation related to chronic smoking appears to result from both a direct, non-sympathoadrenally mediated activation which is rapidly inducible and reversible as well as a more persistent activation which long outlasts the smoke exposure. This latter mechanism appears to result from persistent vascular damage as reflected by the enhanced prostacyclin metabolite excretion. The acute, direct effect of smoking on the platelet appears to be a minor component of the altered platelet function. This latter inference may account for the inability in some studies to observe a small incremental, acute change superimposed on the persistently increased platelet reactivity secondary to the enhanced interactions with a damaged vasculature.

Coronary thrombosis and platelet/fibrin microemboli in death associated with acute myocardial infarction

The frequency and clinical significance of platelet/fibrin microemboli in the microcirculation were investigated in 24 patients whose deaths (before and during hospital admission) were associated with acute myocardial infarction. An acute coronary thrombus was present in all the hearts. In nine hearts an acute thrombus was found in more than one major epicardial coronary artery. A total of 35 acute thrombi were found in the 24 hearts. Platelet/fibrin microemboli were found in 19 (79%) hearts. Eighteen patients died in hospital. The hearts of 16 of these cases showed microemboli; 16 had important arrhythmias or various forms of heart block; 13 showed acute pathological changes in the conduction system. Fourteen of the deaths in hospital were primarily the result of cardiogenic shock and four were primarily caused by arrhythmia. Six of the deaths that occurred before admission to hospital were regarded as being arrhythmic in origin. Three of these showed microemboli and the other three had acute pathological changes in the conduction system. Microemboli were found in two (24%) of 12 control hearts. Coronary thrombosis was found in most deaths caused by acute myocardial infarction and platelet/fibrin microemboli were present in the majority of such hearts. These may arise from the coronary thrombus in the larger upstream vessel supplying the microcirculation.

Intravascular platelet activation in the hemolytic uremic syndrome

We studied intravascular platelet activation in patients with typical (epidemic) and atypical (sporadic) HUS and found defective aggregation, decreased platelet and increased plasma serotonin in both groups. The findings were present not only on admission during the thrombocytopenic stage of the disease, but persisted for several weeks after recovery of the platelet count. Reduced endothelial PGI2 production was significantly more common in plasma from atypical than typical cases. Plasma from both typical and atypical HUS patients induced aggregation of normal platelets, but this phenomenon was unrelated to both the presence of thrombocytopenia or the stage of the disease. Serum platelet aggregating activity was higher in the atypical HUS patients, and was not associated with immune complexes detectable by polyethylene glycol precipitation. The data indicate that intravascular platelet activation is a feature of both forms of HUS, and may be initiated by different mechanisms in the two subgroups. While abnormal PGI2 synthesis appears to be important in the atypical cases, neither defective PGI2 production nor platelet aggregation by plasma factors adequately accounts for platelet activation in the majority of typical cases.

Cigarette smoking and hemostatic function

Epidemiologic studies clearly link cigarette smoking with vasoocclusive cardiovascular disease. Postmortem studies provide evidence of accelerated atherogenesis in asymptomatic smokers. However, the rapid regression of cardiovascular risk within the first year of quitting smoking is difficult to explain solely in terms of vascular disease. Recent evidence indicates that plasma fibrinogen, which has been prospectively associated with the risk of ischemic heart disease, is elevated in smokers. Similarly, results from studies investigating thromboxane metabolite excretion in urine confirm those involving radiolabeled platelet turnover, suggesting that platelets are activated in the circulation of chronic smokers. Altered hemostatic function, either as a direct result of smoking or caused by smoking-induced vascular damage, may account for the more rapidly reversible component of cardiovascular risk observed in chronic smokers.

In vivo administration of antibodies against type I collagen in rat: the specific accumulation in spleen

[125I]-labelled rabbit antibodies against rat type I collagen and non-immune IgG were injected into rat circulation. The kinetics of their clearance and the biodistribution in different organs were studied. Both preparations showed very similar clearance rate, the kinetics fitting bi-exponential approximation with characteristic parameters t1,1/2 = 201 +/- 20 min before 320 min and t2,1/2 = 1350 +/- 450 min at times over 320 min for antibodies and 258 +/- 45 min and 890 +/- 140 min for IgG. The specific affinity of the circulating antibodies did not decrease within 24 hours. The antibodies were specifically accumulated in spleen, where their accumulation was 5-fold higher than that of non-immune IgG. Accumulation of antibodies was maximal 3 hours after the injection. The localization ratio (i.e. the ratio of the amount of the antibodies per g of tissue to that per g of blood) reached a maximum 24 hours after the injection and remained stable for 120 hours. Immunofluorescent staining of spleen sections resulted in a bright fluorescence of dense collagenous structures in the trabeculae and in the wall of the central follicular arterium, bright spot fluorescence in the marginal zone of the follicle, and diffuse fluorescence in the red pulp. These findings suggest an unusually high accessibility of collagen type I in spleen to circulating blood plasma components.

Association of polymorphonuclear leukocytes with sites of aortic catheter-induced injury in rabbits

The kinetics of the association of polymorphonuclear leukocytes (PMNs) with arterial balloon catheter-induced injury have been examined. An average of 6 X 10(7) PMNs were isolated from 20 ml of blood and labelled with 111In-oxine for reinfusion into the donor rabbit. The cells remained viable as demonstrated by both in vitro and in vivo tests of cell function. The abdominal aorta of rabbits was denuded of endothelium and immediately, 24 h, or 5 weeks later, exposed to autologous radiolabelled PMNs for 1 h. The presence of PMNs at sites of denudation was demonstrated by detection of the radioactive label and was confirmed by light and electron microscopy after 24 h, but not at 5 weeks. Immediately following denudation radioactivity was 2.44 +/- 0.33 times control (P = 0.006); 2.52 +/- 0.18 at 24 h (P = 0.005); and 1.88 +/- 0.32 times control at 5 weeks (P = 0.045). The presence of PMNs, or their products, 5 weeks after denudation suggests a more complex role of PMNs and possibly a direct involvement in the long term changes resulting from arterial balloon catheter injury.

Biochemical evidence of a chronic abnormality in platelet and vascular function in healthy individuals who smoke cigarettes

Cigarette smoking is associated with increased mortality from cardiovascular disease that declines after cessation. This study extends the evidence regarding the effects of chronic smoking on platelets and the vessel wall in vivo. Excretion of a major urinary thromboxane metabolite, 2,3-dinor-thromboxane B2, is significantly (p less than .01) elevated in apparently healthy chronic smokers (20 cigarettes daily) compared with that in nonsmoking control subjects. This difference in excretion of 2,3-dinor-thromboxane B2 was abolished by the administration of 20 mg aspirin twice daily, a dose shown to selectively inhibit platelet cyclooxygenase. After aspirin, the return of the excretion of 2,3-dinor-thromboxane B2 to pretreatment levels paralleled the recovery of platelet cyclooxygenase. These findings indicate that excessive thromboxane A2 generation in chronic smokers predominantly derives from platelets. The urinary excretion of the prostacyclin metabolite 2,3-dinor-6-keto-prostaglandin F1 alpha also is increased during chronic cigarette smoking, as is the case with other diseases associated with accelerated interaction of platelets with the vessel wall. We have found evidence of platelet and vascular dysfunction in vivo in chronic cigarette smokers before the manifestation of overt cardiovascular disease. The results would also be consistent with the hypothesis that in chronic smokers, the platelet defect is largely reflective of smoking-induced vascular injury.

Effects of a low-fat, low-cholesterol diet on serum lipids, platelet aggregation and thromboxane formation

The purpose of this study was to test the effects of a low-fat, low-cholesterol diet on serum lipids, platelet aggregation, thromboxane formation and blood pressure. Fifteen hyperlipidemic males with normal blood pressure were treated for 2 weeks. Resting supine blood pressure, total serum cholesterol, HDL-cholesterol, the ratio of total cholesterol/HDL-cholesterol and triglycerides all were significantly reduced. The maximum aggregation and velocity of aggregation for isolated platelets stimulated with either ADP or collagen was significantly reduced. Thromboxane formation during 5 min of platelet aggregation with collagen or ADP was also significantly reduced. These results have important implications for hypertension and atherosclerotic cardiovascular disease.

Common mechanisms of proliferation of smooth muscle in atherosclerosis and hypertension

At least two exogenous sources of agents able to control vascular smooth muscle proliferation can be identified. Platelets contain and release mitogens as well as a factor, TGF-beta, that inhibits cell growth on plastic surfaces while stimulating it when cells are grown in suspension in soft agar. Macrophages release mitogens, including PGDF, and macrophage invasion is characteristic of early experimental lesions in fat-fed animals. Finally, it is at least possible that endothelial cell production of mitogens may represent a response to some as yet undefined external injury. The vessel wall also offers sources of growth control endogenous to the smooth muscle cell layers. The vessel wall contains heparan sulfate able to inhibit cell growth of smooth muscle cells, which by themselves can synthesize PDGF. This provides possible positive and negative control of replication intrinsic to the smooth muscle cells themselves. The role of these intrinsic or extrinsic factors in the smooth muscle proliferation of hypertension and atherosclerosis remains hypothetical. It is intriguing to implicate platelets and/or macrophages in the denuding injuries seen in small hypertensive vessels and in advancing atherosclerotic plaques. At least for the latter case, however, there seem to be other critical factors. Simple denudation and thrombosis, for example, are not sufficient to stimulate smooth muscle growth, and the kinetics of proliferation after balloon denudation imply the presence of some other event required to initiate smooth muscle proliferation. Similarly, smooth muscle replication in large vessels of hypertensive animals occurs without loss of endothelial continuity. This implies that replication in response to hypertension depends on factors intrinsic to the vessel wall. Benditt's observation of monoclonality also implies some intrinsic mechanism allowing cells to grow in a focal manner. It is intriguing to consider the possibility that this commitment process could require the release of cells from the intrinsic inhibitory effects of heparan sulfate located around the cells or the synthesis of growth factors secreted by the smooth muscle cells themselves. If we add the hypothesis that only some cells are capable of such a response, we would expect the sort of oligodense phenomenon demonstrated by Benditt. Proof of such a hypothesis, however, will have to await development of methods to explore these mechanisms directly in the vessel wall responding to injury.

Proteoglycan composition of rabbit arterial wall under conditions of experimentally induced atherosclerosis

The concentration and composition of proteoglycans (PG) of the neointima developed following balloon catheter removal of aortic endothelium in rabbits, were assessed. PG were extracted from the aortic intimal-medial tissues with 4 M guanidinium chloride in the presence of protease inhibitors and purified subsequently by cesium chloride gradient ultracentrifugation and fractionation by high-performance liquid chromatography (HPLC). PG so obtained was analysed for its protein, cholesterol and glycosaminoglycan (GAG) content. For the characterization of the GAG moiety, an exhaustive proteolytic digestion was done. The GAG were then recovered by ethanolic precipitation and their relative distribution was determined after a selective enzymatic digestion using specific enzymes. Results show a significant increase in the amount of PG in the areas of the injured arterial wall covered by regenerated endothelium. In addition, changes in the composition of GAG were also found in the PG isolated from experimental animals when compared to PG isolated from normal aorta. A marked increase in the content of chondroitin sulfates and dermatan sulfate of injured tissue was seen. Hyaluronic acid content also changed in response to de-endothelialization and cholesterol feeding, but only moderately. The content of heparan sulfate remained unaffected in experimental tissues. Furthermore, cholesterol feeding aggravated the injury-induced increment of GAG. These findings are consistent with previously reported morphological observations, and correlate well with reports that arterial injury and cholesterol feeding act synergistically in the evolution of the atherosclerotic lesion and provide further evidence that the interaction of lipid and PG of the arterial wall may be of particular importance to our comprehension of the pathogenesis of atherosclerosis.

Immunotargeting of erythrocyte-bound streptokinase provides local lysis of a fibrin clot

The creation of an anticollagen antibody-erythrocyte-streptokinase complex has been described. Immobilization of both proteins on erythrocyte membrane has been performed using an avidin-biotin interaction. Modification of streptokinase with (6-biotinylamido)hexanoic acid N-hydroxysuccinimide ester at the concentration of 1.1 mM (20% modification of protein amino groups) provides effective (up to 90%) attachment of streptokinase to an avidin-carrying erythrocyte surface. The loss of streptokinase activity due to modification under these conditions is not significant. The maximal attachment of streptokinase was equal to about 50 ng per 10(6) erythrocytes, i.e., about 5 X 10(5) molecules of streptokinase per erythrocyte. The presence of streptokinase in the incubation mixture inhibited the attachment of antibodies by about 50%. Nevertheless, co-immobilization of anticollagen antibody (1.0 X 10(5) molecules per cell) and streptokinase (2.8 X 10(5) molecules per cell) on the erythrocyte surface provided firm and specific binding of such erythrocytes to a collagen-coated surface (1.6 X 10(6) bound cells per 1 cm2 on a collagen-coated surface against 0.006 X 10(6) bound cells on a bovine serum albumin-coated surface). Targeting of such erythrocytes led to local lysis of a fibrin clot in the target zone. The properties described offer in principle the possibility of the application of this or a similar system of fibrinolytic agent targeting for the preventive therapy of rethrombosis during surgical manipulations on vessels.

Inhibition of endothelial regeneration by type-beta transforming growth factor from platelets

Damage to the vessel wall is a signal for endothelial migration and replication and for platelet release at the site of injury. Addition of transforming growth factor-beta (TGF-beta) purified from platelets to growing aortic endothelial cells inhibited [3H]thymidine incorporation in a concentration-dependent manner. A transient inhibition of DNA synthesis was also observed in response to wounding; cell migration and replication are inhibited during the first 24 hours after wounding. By 48 hours after wounding both TGF-beta-treated and -untreated cultures showed similar responses. Flow microfluorimetric analysis of cell cycle distribution indicated that after 24 hours of exposure to TGF-beta the cells were blocked from entering S phase, and the fraction of cells in G1 was increased. The inhibition of the initiation of regeneration by TGF-beta could allow time for recruitment of smooth muscle cells into the site of injury by other platelet components.

Effect of dextran 70 and saline on thrombus formation following arteriotomy and intimectomy in small arteries

Twenty-four arteries of rabbit ears, divided into three groups of eight, were prepared and 32P-platelets injected. Arteriotomy (7 mm) and intimectomy (5 mm) were performed and in vivo platelet accumulation followed for 2 hours. Group A comprised untreated control animals, group B was treated with 17 ml saline/kg bw, and group C with 1 g dextran and 17 ml saline/kg bw (Macrodex). Significant differences in platelet accumulation were observed only between the control and Macrodex groups at 105 and 120 minutes. In the control and saline groups four of eight vessels showed poor or no patency. All Macrodex vessels showed good patency. Control and saline vessels had large amounts of red thrombotic material, except for three saline cases with small amounts. After Macrodex treatment five of eight vessels were apparently clean, while the other three showed only small amounts of red thrombotic material. Dextran seems not to influence platelet function but rather to inhibit fibrin stabilization and probably increases fibrinolysis. Vascular patency was only endangered by the formation of solid fibrin-containing red thrombi.

Fatty acid composition of platelets and of plasma lipid esters in relation to platelet function in patients with ischaemic heart disease

Serum lipoproteins, fatty acids in plasma lipid esters and in platelet phospholipids were assessed in 64 patients with ischaemic heart disease (IHD) and in 67 controls. Hyperlipoproteinemia (HLP) (VLDL triglycerides greater than 1.4 mmol/l and/or LDL cholesterol greater than 5.2 mmol/l) was found in 64% of the patients. In the plasma lipid esters the relative concentrations of saturated and monounsaturated fatty acids as well as dihomo-gammalinolenic acid were higher in the IHD patients whereas the linoleic acid concentrations were lower. The altered fatty acid pattern was apparent both in patients with and without HLP. In the platelet phospholipids there was a relative increase of oleic acid and a decrease of stearic acid. The relative content of eicosapentaenoic acid was slightly reduced whereas the linoleic acid concentrations were unchanged compared to the controls. Platelet aggregation induced by ADP and collagen was enhanced in the IHD patients. The lowest threshold value for ADP-induced aggregation was found in the normolipidemic patients. Since there were almost no differences in the relative contents of the long-chain polyunsaturated fatty acids in the platelet phospholipids between patients and controls it is concluded that mechanisms other than the prostaglandin-mediated pathway may contribute to the increased platelet aggregation in IHD patients.