In vivo dynamic real-time monitoring and quantification of platelet-thrombus formation: use of a local isotope detector

Injury Length and Arteriole Constriction Shape Clot Growth and Blood-Flow Acceleration in a Mouse Model of Thrombosis

OBJECTIVE

Quantitative relationships between the extent of injury and thrombus formation in vivo are not well understood. Moreover, it has not been investigated how increased injury severity translates to blood-flow modulation. Here, we investigated interconnections between injury length, clot growth, and blood flow in a mouse model of laser-induced thrombosis. Approach and Results: Using intravital microscopy, we analyzed 59 clotting events collected from the cremaster arteriole of 14 adult mice. We regarded injury length as a measure of injury severity. The injury caused transient constriction upstream and downstream of the injury site resulting in a 50% reduction in arteriole diameter. The amount of platelet accumulation and fibrin formation did not depend on arteriole diameter or deformation but displayed an exponentially increasing dependence on injury length. The height of the platelet clot depended linearly on injury length and the arteriole diameter. Upstream arteriolar constriction correlated with delayed upstream velocity increase, which, in turn, determined downstream velocity. Before clot formation, flow velocity positively correlated with the arteriole diameter. After the onset of thrombus growth, flow velocity at the injury site negatively correlated with the arteriole diameter and with the size of the above-clot lumen.

CONCLUSIONS

Injury severity increased platelet accumulation and fibrin formation in a persistently steep fashion and, together with arteriole diameter, defined clot height. Arterial constriction and clot formation were characterized by a dynamic change in the blood flow, associated with increased flow velocity.

Neurological deficits associated with the elastase-induced aneurysm model in rabbits

OBJECTIVE

Although the rabbit elastase-induced aneurysm model is currently used widely for endovascular research and device testing, procedural causes leading to animal morbidity and mortality have not yet been clearly described. We conducted a retrospective study to analyse factors contributing to neurological deficits in rabbits that underwent the elastase-induced aneurysm creation procedure at our research center from 2002 to 2005 in order to improve the technique and reduce procedure-related morbidity and mortality.

METHODS

A total sample of 38 animals that underwent the procedure under the same conditions was analysed in two groups: animals that presented neurological deficits (ND, n=15) and animals that were neurological deficit free (NDF, n=23). Data were collected by reviewing the animal records and radiographic images from the procedures. Statistical analyses using the Mann-Whitney test, unpaired t-test with Welch correction and Fisher's exact tests were performed to compare the two groups based on variables associated with endothelial injury and activation of the coagulation cascade.

RESULTS

The variables of animal weight (signifying state of health of the animal), total procedure time, total balloon occlusion time and clot formation were found to be significantly and/or very significantly correlated to ND presentation.

DISCUSSION

Successful creation of the rabbit elastase-induced aneurysm model depends on careful control over several technical details. Important variables governing outcome have been identified here. A specific, improved endovascular arrangement that facilitates maneuvering of the devices and reduces the risk of air emboli is presented.

Influence of radiofrequency catheter ablation on platelet aggregation

The objective of this article was to find out how radiofrequency catheter ablation (RFA) influences platelet aggregation (PA), and the dependence on the total energy (TE) of RFA used and the cause of arrhythmia. We investigated 97 patients. PA was analyzed before, after, and in 24 hours after RFA. ADP- and epinephrine-induced PA significantly decreased after RFA by 5% and 8.9% (P < .001), respectively, and increased in 24 hours close to baseline. PA induced by ADP and collagen did not radically depend on the TE. Epinephrine-induced PA decreased after RFA by 0%, 8% (P < .05), and 16.9% (P < .01) in groups of patients where the TEs used were <4000 J, 4000 to 15,000 J, and >15,000 J, respectively. There were no significant differences in PA between groups based on the cause of arrhythmia. ADP- and epinephrine-induced PA significantly decreased after RFA and returned close to baseline in 24 hours. Epinephrine-induced PA was inversely associated with the TE used for RFA.

Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: effect on platelet aggregation and coagulation

Endothelial-derived proteoglycans are important regulators of the coagulation-pathway in vivo and our primary objective of this study was to determine whether chronic shear stress affected the synthesis, release, and activity of proteoglycans from bovine aortic endothelial cells (BAEC). BAEC were cultured under shear and proteoglycans were purified from BAEC conditioned media and analyzed using both anionic exchange and size exclusion chromatography. The overall amount of proteoglycans produced per cell was significantly greater for the high shear-treated samples compared to the low shear-treated samples indicating that the shear magnitude did impact cell responsiveness. While overall size and composition of the proteoglycans and glycosaminoglycan (GAG) side chains were not altered by shear, the relative proportion of the high and low molecular weight species was inversely related to shear and differed significantly from that found under static tissue culture conditions. Moreover, a unique proteoglycan peak was identified from low shear stress (5 +/- 2 dynes/cm(2)) conditioned media when compared to high shear conditions (23 +/- 8 dynes/cm(2)) via anionic exchange chromatography, suggesting that subtle changes in the GAG structures may impact activity of these molecules. In order to characterize whether these changes impacted proteoglycan function, we studied the effects of shear specific proteoglycans on the inhibition of thrombin-induced human platelet aggregation as well as on platelet-fibrin clot dynamics. Proteoglycans from high shear-treated samples were less effective inhibitors of both platelet aggregation and blood coagulation inhibition than proteoglycans from low shear-treated samples and both were less effective than proteoglycans isolated from static tissue culture samples. However, due to changes in the overall proteoglycan synthesis and release rate, the high and low shear-treated sample had essentially identical effects on these activities, suggesting that the cells were able to compensate for stress-induced proteoglycan changes. Our data suggests that shear stress, by altering proteoglycan synthesis and fine structure, may play a role in maintaining vascular hemodynamics and hemostasis.

A comparative thrombogenicity study of heparin soaked fluoro-passivated polyester and ePTFE patches in sheep

OBJECTIVES

to compare heparin soaked fluoro-passivated gelatine sealed polyester and expanded polytetrafluoroethylene (ePTFE) patches in a sheep model of acute platelet accumulation following patch angioplasty.

MATERIALS AND METHODS

heparin soaked patches were placed in the carotid arteries of 9 sheep and autologous (111)Indium labelled platelets were infused. The patches were explanted two hours after the injection of labelled platelets. Median specimen radioactivity was calculated as a ratio of radioactivity in explanted and in 4 ml of blood. Explanted patches were also investigated by scanning electron microscopy (SEM).

RESULTS

platelet accumulation was significantly greater on ePTFE patches. For both materials platelet accumulation was greater at the distal end compared to the proximal (p<0.05). SEM demonstrated more platelets as well as thicker thrombus layer on ePTFE-patches.

CONCLUSION

in sheep carotid arteries, a fluoropassivated gelatine sealed polyester patch appears to result in less platelet accumulation when compared to ePTFE.

A novel platelet-rich arterial thrombosis model in rabbits. Simple, reproducible, and dynamic real-time measurement by using double-opposing inverted-sutures model

Though numerous animal thrombosis models have been introduced, an easy, reliable, and reproducible arterial thrombosis model remains a continuing challenge prior to a thrombolytic study. In an effort to evaluate the efficiency of various recombinant thrombolytic agents with specific affinity to activated platelets in vivo, we developed a novel double-opposing inverted-sutures model to create a platelet-rich thrombus in the femoral artery of rabbits. The arteriotomy was done semicircumferentially, and variously sized microsurgical sutures were introduced intraluminally in a double-opposing inverted manner. The animals were divided into three groups according to the double-opposing inverted-sutures used: Group 1 with 10-0 nylon (n=6), Group 2 with 9-0 nylon (n=6), and Group 3 with 8-0 nylon (n=22). The superficial epigastric branch was cannulated with a thin polyethylene (PE) tube for intraarterial administration of the studied thrombolytic agent. The blood flow was continuously measured with a real-time ultrasonic flow meter. Within 2 h of installation of the sutures, there was no thrombus formation in either Group 1 or 2. In Group 3, the thrombosis rate was 91% (20 of 22) under a steady baseline flow (with an average of 12.23+/-2.40 ml/min). It was highly statistically significant with a P-value of .0000743 using Fisher's Exact Test. The averaged time to thrombosis was 21.8+/-9.8 min. The ultrasonic flow meter to record the dynamic real-time measurement of blood flow was a guideline for thrombus formation or dissolution, which was correlated with the morphological findings of stenotic status of the vessel detected by the Doppler sonography. The components of the thrombus were proven to be platelet-rich predominant by histological examination via hematoxylin and eosin (H&E) stain and transmission electron microscopy (TEM). To confirm that the double-opposing inverted-sutures model would be useful for a study of thrombolytic agents, we evaluated the effects of recombinant tissue-type plasminogen activator (rt-PA) and streptokinase-human plasminogen (SK-HPlg). The average time to thrombolysis post rt-PA infusion was 16.0+/-8.2 min and that of SK-HPlg was 79.6+/-23.1, which were similar to the previous reports. In conclusion, the novel double-opposing inverted-sutures (8-0 nylon) model provides a simple, reliable, and reproducible platelet-rich arterial thrombosis model with noninvasive and dynamic real-time measurement. It may be applied in assessing the efficiency of the recombinant thrombolytic agents and offers many advantages of an arterial platelet-rich in vivo thrombosis model.

Antithrombotic effects of abciximab

The observation that platelet-platelet interaction and thrombosis are ultimately regulated by the glycoprotein (GP) IIb/IIIa receptor complex, triggered the development of agents capable of interfering with this platelet receptor complex. Several large clinical trials have demonstrated the effectiveness of this class of agents. The first of these agents to show beneficial effects after coronary interventions was the mouse/human chimeric Fab fragment antibody c7E3 (abciximab; ReoPro). This study analyzes whether the addition of heparin to the GP IIb/IIIa antagonist abciximab would enhance the antithrombotic effect. Blood drawn directly from patients on aspirin who underwent interventional procedures perfused an ex vivo perfusion chamber containing a severely injured arterial wall at local rheologic conditions of a mildly stenosed coronary artery. Blood was perfused directly from patients at baseline and following administration of heparin, abciximab, or both. The antithrombotic effects of the 3 treatments were assessed by reduction of the thrombus formation on the perfused specimens. Thrombus formation at baseline was not significantly modified by the administration of heparin (13,897 +/- 1,316 vs 11,917 +/- 1,519 microm(2)). Abciximab produced a 58% reduction in thrombus formation (11,631 +/- 861 vs 4, 925 +/- 585 microm(2); p <0.001). The addition of heparin to abciximab did not further reduce thrombus area versus abciximab alone (5,651 +/- 581 vs 4,925 +/- 585 microm(2)). Thus, our data show that abciximab dramatically decreases mural thrombus formation and that combining heparin with abciximab did not add any additional antithrombotic effect to abciximab alone.