Flow-based assays for global assessment of hemostasis. Part 1: Biorheologic considerations.
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Blood Coagulation↗
Biomedical subjects
K S Sakariassen
Publications and source records attributed to K S Sakariassen.
Flow-based assays for global assessment of hemostasis. Part 2: current methods and considerations for the future.
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Blood Coagulation Disorders↗
Recollections of the development of flow devices for studying mechanisms of hemostasis and thrombosis in flowing whole blood.
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Animals↗
Role of 4 platelet membrane glycoprotein polymorphisms on experimental arterial thrombus formation in men.
This study investigates whether the polymorphisms of 3 important platelet receptors affected experimental thrombus formation in men. Forty healthy male volunteers randomly recruited were genotyped for the variable number of tandem repeat (VNTR) of GPIbalpha, the -5T/C polymorphism in the Kozak sequence of GPIbalpha, the 807C/T polymorphism of GPIa, and the PI(A1)/PI(A2) polymorphism of GPIIb/IIIa. Platelet thrombus formation was induced ex vivo by exposing a collagen-coated coverslip in a parallel plate perfusion chamber to native blood for 4 minutes. The shear rates at the collagen surface were 650 and 2600 x s(-1). At 2600 x s(-1) platelet thrombus formation was significantly related only to the 807C/T polymorphism. In contrast, at 650 x s(-1) thrombus formation was significantly altered only by the Kozak sequence polymorphism. The VNTR and the PI(A1)/PI(A2) polymorphisms did not influence thrombus formation. Thus, platelet thrombus formation is significantly influenced by genetic variations of the GPIbalpha and GPIa receptors. The effect of these polymorphisms was dependent on the blood flow rate.
Adult↗
Methods and models to evaluate shear-dependent and surface reactivity-dependent antithrombotic efficacy.
The purpose of the present communication is to evaluate the importance of blood flow and surface reactivity for measurement of antithrombotic drug activity or efficacy in selected model systems of thrombus formation. Such information is essential for proper evaluation of antithrombotic drug profiles. The continuous development of flow-dependent thrombosis models for in vitro (anticoagulated blood) and ex vivo (native blood) studies and their application in in vivo animal models from the early 1970s and onwards are briefly considered. Central to this process was the development of various types of perfusion chambers in which a thrombogenic surface is exposed to flowing blood. Such perfusion chambers have been inserted into arteriovenous (AV) shunts in baboon, pig, dog, and rabbit. These approaches have allowed reproducible testing of traditional and novel experimental antithrombotic drugs, and studies on novel drug strategies under well-defined shear conditions and surface reactivity. Shear-dependent antithrombotic efficacy in these models is observed with anticoagulants such as unfractionated heparin, low-molecular weight heparins, or selective inhibitors of thrombin, Factor Xa, or Factor VIIa. However, the degree of shear dependency depends on the nature of the thrombogenic surface, e.g., the inhibition is more pronounced on a tissue factor (TF)-rich surface than on a collagen-rich surface, particularly at venous or low arterial shear. Platelet antagonists such as the COX-1 inhibitor aspirin, inhibitors of thromboxane A2 (TxA2) synthetase, the TxA2 platelet receptor, and of von Willebrand factor (vWf) are shear dependent also, being more efficient at high arterial shear. In contrast, the platelet ADP antagonist clopidogrel, or antagonists to the active platelet membrane glycoprotein IIb-IIIa complex (GPIIb-IIIa) are shear independent. At extremely high arterial shear, which activates platelets and elicit aggregates of circulating platelets, aspirin looses its antithrombotic effect, whereas ADP and GPIIb-IIIa antagonists still interrupt thrombus formation. In general, results obtained with these models mimic and predict antithrombotic efficacy in man when comparison is possible. Information on antithrombotic efficacy in flow devices with various thrombogenic surfaces is now sufficiently available to suggest recommendations for experimental conditions, particularly with regard to blood flow and reactive surfaces.
Animals↗
5-aminoimidazole-4-carboxy-amide-1-beta-D-ribofuranoside treatment ameliorates hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice.
AIM/HYPOTHESIS: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside increases 5'-AMP-activated kinase activity in insulin-sensitive tissues known to control glucose homeostasis. We hypothesised that 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment could have a beneficial effect on glucose homeostasis in KKAy-CETP mice, a model of Type II (non-insulin-dependent) diabetes mellitus. Our aim was to examine potential effects of acute and chronic (7-day) 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment on glucose homeostasis in KKAy-CETP diabetic mice. METHODS: Female KKAy-CETP mice were treated with 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside by a single daily injection for 7 days (100, 300, or 500 mg. kg-1. day-1). RESULTS: After 7 days of treatment with 500 mg. kg-1. day-1 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside, blood glucose and plasma insulin concentrations were reduced (p < 0.01). Body weight and food intake were also reduced after treatment (p < 0.01 and p < 0.05, respectively). Glucose and insulin tolerance were improved (p < 0.05), whereas endogenous glucose production was suppressed (p < 0.05). The beneficial effect of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside on hyperglycaemia and hyperinsulinaemia was due to an inhibition of endogenous glucose production, since in vivo and in vitro basal and insulin-stimulated glucose uptake in skeletal muscle was not affected by 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside. Other features of the treatment included increased plasma of free fatty acid concentration (1.9-fold, p < 0.01) and triglycerides (1.3-fold, p < 0.05). CONCLUSION/INTERPRETATION: 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside treatment attenuated hyperglycaemia and hyperinsulinaemia but not dyslipidaemia in KKAy-CETP mice, a model of Type II diabetes. The blood glucose lowering effects of 5-aminoimidazole-4-carboxy-amide-1-beta-d-ribofuranoside occurs mainly as a consequence of reduced endogenous glucose production because insulin-stimulated skeletal muscle glucose uptake has not been altered.
Aminoimidazole Carboxamide↗
Effect of radiologic contrast media on cell volume regulation in rabbit proximal renal tubules.
RATIONALE AND OBJECTIVES: Most radiographic contrast media are hyperosmotic and able to shrink cells with which they are in contact. The authors studied cell volume control in rabbit proximal renal tubules after incubation with three contrast media: iohexol, ioxaglate, and iodixanol. MATERIALS AND METHODS: Proximal renal tubules were isolated from rabbit kidneys. The tubules were exposed to Ringer solutions containing 5% vol/vol iohexol (final osmolality, 330 mOsm), ioxaglate (323 mOsm), iodixanol (305 mOsm), or mannitol (control solutions with identical osmolalities), and tubule volumes were monitored. After 2 hours of incubation, the tubules were stimulated with a hyposmotic Ringer solution (165 mOsm). Three groups of 10 experiments were performed. RESULTS: All solutions induced cell shrinkage (8.3%+/-3.8 [standard error] to 15.4%+/-0.5), which was completely or partly reversible in most experiments (volume increase, 44.8%+/-14.7 to 149.9%+/-107.3) but not those with iohexol and iodixanol. With exposure to the hyposmotic solution, the cells swelled by 11.0%+/-1.8 to 39.7%+/-4.8. In general, the tubules that had been exposed to the most hyperosmotic solution swelled the most. Those exposed to contrast media showed less swelling than the mannitol-exposed controls. In all control experiments, the cells exhibited a gradual shrinkage (43.6%+/-28.5 to 87.0%+/-13). This regulatory response was partly inhibited in tubules exposed to iohexol (39.9%+/-15.8 shrinkage) or iodixanol (8.9%+/-15.8) and completely inhibited in those exposed to ioxaglate. Iohexol and ioxaglate exposure also led to a decrease in water permeability. CONCLUSION: Exposure to hyperosmotic contrast medium tends to induce prolonged cell shrinkage, decrease the water permeability of the cellular plasma membranes, and compromise the ability to regulate cellular volume. These changes seem to reflect both the hyperosmolality of the solutions and their inherent chemical properties.
Animals↗
Synthesis, biological activity, and solution structures of a cyclic dodecapeptide from the EGF-2 domain of blood coagulation factor VII.
The cyclic dodecapeptide, disulfide-cyclo-[H-Cys-Val-Asn-Glu-Asn-Gly-Gly-Cys(Acm)-Glu-Gln-Tyr-Cys-OH], which corresponds to the 91-102 sequence of the second epidermal growth factor domain of human blood coagulation factor VII, was synthesized using solid-phase procedures. It was shown to be an inhibitor at the key step in the induction of coagulation by the extrinsic pathway, i.e. the factor VII/tissue factor-catalyzed activation of coagulation factor X. The solution structure of this peptide was investigated by NMR spectroscopy and was computer-modeled via molecular mechanics. Structures were calculated based on 112 distance and nine dihedral angle constraints. The resulting backbone structures were classified into two structural subsets: one which exhibited a twisted '8'-shaped folding and another describing an open, circular 'O' outline. The local backbone structures of segments Asn3-Glu4-Asn5, Gly7-Cys8 and Gln10-Tyr11 were well preserved among the two subsets. Apart from the unrestrained N- and C-termini, Gly6 and Glu9 sites exhibited marked local disorder between the two subsets, suggesting localized flexible hinges likely to govern tertiary structure interconversion between the two subsets. Two transient hydrogen bonds were identified from pH chemical shift titrations by matching the pKa values of NH and carboxylate groups, which supported the occurrence of the '8' structure, and agreed with temperature coefficients of peptidyl NH resonances. Structure-function relationships of the peptide were discussed in terms of the likely physiological function of the disulfide-bonded loop in factor VII which the peptide represents.
Amides↗
Effect of radiologic contrast material on cell volume regulation in proximal renal tubules from trout (Salmo trutta).
RATIONALE AND OBJECTIVES: Most radiographic contrast media (CM) are hyperosmotic and pose an osmotic threat to cells they are in contact with. To study these effects at the cellular level, cell volume regulatory mechanisms were observed in proximal renal tubules following exposure to the CM iohexol, ioxaglate, and iodixanol. MATERIALS AND METHODS: Isolated renal tubules from trout (Salmo trutta) were exposed to 5% vol/vol iohexol (326 mOsm), ioxaglate (314 mOsm), or iodixanol (300 mOsm) or mannitol (to achieve the same osmolalities), and cell volume changes were observed videometrically. RESULTS: Iohexol and ioxaglate solutions induced a rapid shrinkage (12%-13%) not followed by cell volume regulation. Without CM (same osmolality), the cells shrank 11% but then showed a 77%-88% volume recovery. This reswelling was inhibited by 55% with the Na+, K+, Cl- symporter inhibitor bumetanide (50 micromol/L). Iodixanol did not significantly affect cell volume. Tubules preincubated with CM or mannitol were then stimulated with a hypoosmotic Ringer solution (160 mOsm) resulting in a 26%-36% cellular volume increase. Compared with results of experiments without mannitol and CM, preexposure to iohexol or ioxaglate almost completely inhibited the expected regulatory shrinkage phase, while previous exposure to hyperosmotic solutions with mannitol reduced the shrinkage response by 40%-53%. CONCLUSION: In this system, the hyperosmotic iohexol and ioxaglate cause cell shrinkage followed by an impaired cell volume regulatory response. Exposure to these two CM also inhibits cell volume regulation on hypoosmotic stimulation. The isosmotic iodixanol has no such effects. These changes appear to some extent to be a result of the CM's degree of hyperosmolality, but this property alone does not explain these findings.
Animals↗
Protamine sulphate inhibits platelet membrane glycoprotein Ib-von Willebrand factor activity.
Platelet adhesion to the injured vessel wall is essential in haemostasis and thrombosis. This process involves the interaction of the platelet glycoprotein Ib (GPIb) with surface bound von Willebrand factor (vWF). Since synthetic polycationic peptides of the general formula (Arg)n, (Lys)n or (Arg-Lys)n inhibit GPIb-vWF interaction, they were suggested as potential antithrombotics. Protamine sulphate is a highly cationic polypeptide, arginine accounting for approximately 60% of the primary sequence, utilized to neutralize the anticoagulant effect of heparin after cardiac surgery. We have investigated potential effects of protamine sulphate on the function of GPIb-vWF. Addition of protamine sulphate to platelet-rich plasma (PRP), reduced significantly the GPIb-vWF activity as assessed by ristocetin-induced platelet agglutination. When protamine sulphate was added to PRP containing heparin, even at clinically relevant neutralizing doses the GPIb-vWF activity was reduced by 20-30% (p < 0.001). Protamine sulphate in excess of heparin nearly abolished the activity. Furthermore, the direct effect of protamine sulphate on collagen-induced platelet thrombus formation in non-anticoagulated human blood was investigated by employing an ex-vivo parallel-plate perfusion chamber device. Protamine sulphate (200 microg/mL) reduced platelet-collagen adhesion at shear rates of 650 and 2600 sec(-1) by 40% (p< 0.004) and 45% (p < 0.0001), respectively. The corresponding platelet thrombus volumes were concomitantly reduced by 90% (p < 0.006) and 84% (p < 0.05). Our data are questioning the rationale for empirical repetitive protamine sulphate administration when so-called "heparin rebound" after cardiac surgery is suspected, since protamine sulphate in excess of heparin may impair the platelet GPIb-vWF interaction necessary for normal haemostasis.
Anticoagulants↗
Phosphorylation sites in the integrin beta3 cytoplasmic domain in intact platelets.
Protein seryl/threonyl phosphatase inhibitors such as calyculin A block inside-out and outside-in platelet signaling. Our studies demonstrate that the addition of calyculin A blocks platelet adhesion and spreading on fibrinogen, responses that depend on integrin alphaIIb beta3 signaling. We hypothesized that this reflects a change in alphaIIb beta3 structure caused by a specific state of phosphorylation. We show that addition of calyculin A leads to increased phosphorylation of the beta3 subunit, and phosphoamino acid analysis reveals that only threonine residues become phosphorylated; sequence analysis by Edman degradation established that threonine 753 became stoichiometrically phosphorylated during inhibition of platelet phosphatases by calyculin A. This region of beta3 is linked to outside-in signaling such as platelet spreading responses. The effect of calyculin A on platelet adhesion and spreading and on the phosphorylation of T-753 in beta3 is reversed by the calcium ionophore A23187, demonstrating that these effects of calyculin A are not generally toxic ones. We propose that phosphorylation of beta3 on threonine 753, a region of beta3 linked to outside-in signaling, may be a mechanism by which integrin alphaIIb beta3 function is regulated.
Blood Platelets↗
Selective venous thrombolysis with the nipple-balloon catheter: comparative evaluation in vivo.
PURPOSE: To compare in an animal model of deep vein thrombosis, an intramural drug delivery catheter, the nipple-balloon catheter, with an occlusion balloon-infusion guide wire system. MATERIALS AND METHODS: Ten juvenile pigs were used for the study. Deep vein thrombosis was induced in both hind limbs by using a previously described technique. Heparin was administered 30 minutes later (2,500 IU intravenously) and bilateral thrombolysis was attempted with use of 8 mg of alteplase as a 0.25 mg/mL solution containing heparin 50 IU/mL (n = 10) and sodium/meglumine ioxaglate 40 mgI2/mL (n = 5). In one limb, the external iliac vein was endoluminally occluded, and 0.8 mL of alteplase was administered every 3 minutes through a multisideport infusion wire placed coaxially through the balloon catheter. On the other side, a nipple-balloon catheter was used: alteplase was injected as two 0.4-mL aliquots every 3 minutes in overlapping segments of the vessel. Blood samples were taken at predetermined intervals to determine the partial thromboplastin time and plasma fibrinogen concentration. At autopsy, the thrombus mass in the iliofemoral veins was measured, and the extent of residual thrombosis in the venous tributaries was graded at four sites. The heart and the lungs were also examined for thromboemboli (n = 5). Venous specimens were then subjected to X-ray fluorescence spectrometry to determine iodine content (n = 5). RESULTS: Bilateral thrombolysis could be successfully completed in all animals. No procedural problem associated with the use of the nipple-balloon catheter was encountered. The mass of residual thrombus in the axial veins was significantly lower in this group (P = .005). The drug delivery system used did not appreciably influence thrombolysis in the tributaries. Signs of macroscopic damage to the veins were not observed in any animal. None of the venous specimens had detectable levels of iodine. Small thromboemboli were found in the pulmonary circulation in three of five animals. Fibrinogen levels did not decrease during the procedure. CONCLUSIONS: The significantly lower residual thrombus burden associated with use of the nipple-balloon catheter suggests that the device may have the potential to be an effective delivery system for selective thrombolysis in veins.
Animals↗
Comparison of the antithrombotic effect of PEG-hirudin and heparin in a human ex vivo model of arterial thrombosis.
Polyethylene glycol (PEG)-hirudin is a derivative of hirudin with a long plasma half-life. We have compared the efficacy of PEG-hirudin with unfractionated heparin (UH) in preventing arterial thrombosis. Arterial thrombus formation was induced ex vivo in 12 healthy human volunteers by exposing a tissue factor-coated coverslip positioned in a parallel-plate perfusion chamber to flowing nonanticoagulated human blood drawn directly from an antecubital vein at an arterial wall shear rate of 2600 s-1 for 3.5 minutes. PEG-hirudin, UH, or saline (as control) were administered ex vivo through a heparin-coated mixing device positioned proximal to the perfusion chamber. Platelet and fibrin deposition was quantified by immunoenzymatic measure of the P-selectin and D-dimer content of dissolved plasmin-digested thrombi, respectively. UH was administered to a plasma concentration of 0.35 IU/mL. This concentration prolonged the activated partial thromboplastin time from 32+/-1 seconds to 79+/-4 seconds (P<0.01). UH did not significantly prevent platelet deposition. However, fibrin deposition was reduced by 39% (P<0.05). PEG-hirudin in plasma concentrations of 0.5, 2.5, and 5 microg/mL prolonged the activated partial thromboplastin time to 48+/-2, 87+/-4, and 118+/-4 seconds, respectively. In contrast to UH, PEG-hirudin prevented both platelet and fibrin deposition in a dose-dependent manner with a >80% reduction at 5 microg/mL (P<0.01). Furthermore, the plasma level of PEG-hirudin required to significantly prevent fibrin deposition (0.5 microg/mL) corresponded to a much shorter prolongation of activated partial thromboplastin time (48+/-2 seconds) than that needed for UH (79+/-4 seconds). Thus, our results are compatible with the view that thrombin is greatly involved in recruitment of platelets in evolving thrombi, and that PEG-hirudin is an effective agent for preventing arterial thrombosis in a human ex vivo experimental model.
Antithrombin III↗
Antithrombotic efficacy of the vitamin K antagonist fluindione in a human Ex vivo model of arterial thrombosis : effect of anticoagulation level and combination therapy with aspirin.
Thrombin is a main mediator of arterial thrombus formation, and its inhibition is an important antithrombotic strategy. However, the place of vitamin K antagonists among the different therapeutic strategies for preventing arterial thrombus formation is still debated. We studied the antithrombotic efficacy of the vitamin K antagonist fluindione in a human ex vivo model of arterial thrombosis and determined whether aspirin enhances fluindione efficacy. Ten healthy male volunteers were randomly assigned to receive fluindione, alone or in combination with aspirin (325 mg/d). Fluindione was given at increasing doses to give a stable international normalized ratio (INR) between 1.5 and 2.0 and between 2.1 and 3.0. We induced arterial thrombus formation ex vivo by exposing collagen- or tissue factor (TF)-coated coverslips in a parallel-plate perfusion chamber to native blood for 3 minutes at an arterial wall shear rate of 2600 s(-1). Platelet and fibrin deposition were measured by immunoenzymatic methods. Fluindione inhibited thrombus formation on TF-coated coverslips in a dose-dependent manner by 50% and 80% at INR 1.5 to 2.0 and INR 2.1 to 3.0, respectively (P<0.05). Fluindione in combination with aspirin inhibited TF-induced thrombus formation in a comparable manner. Collagen-induced thrombus formation was not reduced in subjects treated by fluindione. It was reduced by 50% to 60% in those treated with fluindione plus aspirin, regardless of the level of anticoagulation (P<0.05). Thus, the effectiveness of fluindione for preventing arterial thrombosis is dependent on the nature of the thrombogenic trigger. Fluindione is very effective in preventing TF- but not collagen-triggered thrombus formation. Aspirin enhances the antithrombotic effectiveness of fluindione, because combined treatment interrupts both TF- and collagen-induced thrombus formation.
Adolescent↗
Shear-induced platelet activation and platelet microparticle formation in native human blood.
Shear-induced platelet activation and platelet microparticle formation are triggered in native human blood by high arterial shear or by a sudden increase in shear as introduced by a stenosis with potential consequences for collagen-induced platelet thrombus formation. Blood was drawn from healthy volunteers and directly perfused ex vivo over various well-defined eccentric stenoses. Shear-induced platelet activation was determined by using flow cytometry to assess: 1) GPIIb-IIIa activation by fluorescein isothiocyanate (FITC)-labeled Mab PAC-1; and 2) translocation of membrane aminophospholipids (procoagulant activity) by FITC-labeled Annexin V. Microparticle formation was measured by flow cytometry and FITC-labeled Mab Y2/51 directed against GPIIIa. Significant platelet activation and platelet microparticle formation were elicited when the wall shear rate reached 10,500 sec-1 for a period of 0.075 sec. Prolonged exposure to or a rapid increase in shear further enhanced activation and microparticle formation. Shear-induced platelet activation was associated with significantly increased collagen-induced platelet thrombus formation that was insensitive to aspirin ingestion. Exposure of native blood to very high shear thus activates platelets to express GPIIb-IIIa, renders the platelet membrane procoagulant and stimulates microparticle formation. These responses are associated with enhanced collagen-induced thrombus formation by prostaglandin-independent mechanisms.
Adult↗
A peptide sequence from mouse tissue factor inhibits human tissue factor dependent factor X activation.
Synthetic peptides based on the putative factor X recognition site of human (Thr-Leu-Tyr-Tyr-Trp-Lys-Ser-Ser-Ser-Ser), rabbit (Thr-Leu-Tyr-Tyr-Trp-Arg-Ala-Ser-Ser-Thr), and murine tissue factor (Ile-Ile-Thr-Tyr-Arg-Lys-Gly-Ser-Ser-Thr) were dose-dependent inhibitors of human tissue factor/factor VIIa catalyzed factor X activation with IC50 values of 220, 17, and 33 microM, respectively. The mouse results were highly surprising given the low homology between the human and mouse sequence (40%) and that mouse tissue factor, in contrast with rabbit tissue factor, does not support the procoagulant activity of human factor VIIa on factor X. The inhibitory mechanism of the murine peptide was noncompetitive with respect to factor X but competitive with respect to tissue factor, indicating the peptide competes with tissue factor (or the tissue factor/factor VIIa complex) for binding to factor X. The peptide could be N-terminally truncated by two Ile without loss of inhibitory activity or changed inhibitory mechanism. Substitution of two Gly for the two Ile, which increased solubility, decreased IC50 to 17 microM whereas scrambling the peptide made it inactive.
Amino Acid Sequence↗
Blood flow and antithrombotic drug effects.
This paper reviews the importance of blood flow phenomena in models of experimental thrombosis used for measuring antithrombotic drug efficacy. The characteristics of these systems and their application for studies with human blood and in animal models are considered. Central to these investigations has been the development of various types of perfusion chambers in which a thrombogenic test surface is exposed to flowing blood under well-defined conditions of blood flow and device geometry. Such perfusion chambers, which have been used in vitro, ex vivo, and in vivo by insertion into arteriovenous shunts in various animal species, have allowed reproducible testing of both conventional and experimental agents. Shear-dependent antithrombotic effects have been observed with anticoagulants such as heparin and with selective inhibitors of thrombin, factor Xa, and factor VIIa. However, the degree of shear dependency depends on the chemical composition of the thrombogenic surface; for example, anticoagulant effects may be more pronounced on a tissue factor-rich surface than on a collagen-rich surface, particularly at venous or low arterial shear rates. Platelet inhibitors such as aspirin, thromboxane antagonists, or inhibitors of von Willebrand factor platelet interactions are also shear dependent, being more efficient at high shear rates. In contrast, inhibitors of adenosine diphosphate-dependent platelet reactions or antagonists of the platelet membrane glycoprotein IIb/IIIa complex are shear rate independent. At very high shear rates characteristic of severely stenotic arteries, aspirin loses its direct antithrombotic effect, whereas adenosine diphosphate pathway inhibitors and GP IIb/IIIa antagonists are still beneficial. In general, results obtained with many of these models have predicted antithrombotic efficacy in human beings when comparisons were possible. Therefore shear-dependent models of experimental thrombosis are routinely used in the evaluation of antithrombotic pharmacologic agents, both preclinically and clinically.
Animals↗
Iohexol, platelet activation and thrombosis. I. Iohexol-induced platelet secretion does not affect thrombus formation in native blood.
BACKGROUND: The nonionic monomer iohexol triggers in vitro platelet secretion of beta-thromboglobulin (beta-TG). This iohexol platelet activation may promote intravascular thrombosis. We studied this relationship by employing a human model of collagen-induced platelet thrombus formation at arterial flow. The ionic dimer ioxaglate, the nonionic dimer iodixanol, and glucose were included. METHODS AND RESULTS: In vitro platelet activation as measured by beta-TG secretion following a 1-min incubation of native blood with 50 vol% of iohexol was significant. Glucose solutions of 300, 580 and 825 mosmol, corresponding to the osmolalities of respectively iodixanol, ioxaglate and iohexol, increased the beta-TG secretion in parallel with the osmolalities. Ioxaglate and iodixanol were virtually inert. Continuous infusion of iohexol or 580 or 825 mosmol glucose (40 vol%) into flowing native blood at an arterial wall shear rate of 2600 s-1 in an ex vivo collagen-induced platelet thrombus formation device triggered pronounced secretion of beta-TG. However, the platelet thrombus formation in blood mixed with iohexol was within the same range as that observed with ioxaglate or iodixanol. Increasing glucose osmolality induced increasing beta-TG secretion, which paralleled gradually decreasing platelet thrombus formation. CONCLUSION: Iohexol and 580 or 825 mosmol glucose trigger platelet secretion of beta-TG. This secretion is not associated with enhanced collagen-induced platelet thrombus formation at high arterial shear.
Blood Donors↗