Antithrombotic effects of activated protein C and protein S in a rabbit model of microarterial thrombosis

Spinal Cord Infarction in an Adolescent with Protein S Deficiency: A Case Report and Literature Review

Protein S deficiency causes spinal cord infarction in rare cases. We herein report the first case of severe cervicothoracic cord infarction in an adolescent with protein S deficiency. A 16-year-old boy presented with neck pain, four-limb paralysis, and numbness. Magnetic resonance imaging revealed spinal artery infarction in the C4 to Th4 area. Protein S antigen and activity were decreased. The patient was diagnosed with protein S deficiency-associated cervicothoracic cord infarction, which was treated with anticoagulation. Protein S deficiency should be considered as a potential cause of spinal cord infarction in young healthy patients and should be appropriately treated with anticoagulation.

Polydopamine-modified dual-ligand nanoparticles as highly effective and targeted magnetic resonance/photoacoustic dual-modality thrombus imaging agents

Background

Platelet activation and subsequent aggregation are the initial stages of thrombosis. A molecular probe that specifically targets activated platelets and remains retained under high shear stress in vivo can enhance the imaging effect to achieve early and accurate diagnosis.

Methods and materials

In this study, we constructed nanoparticles (NPs) using polydopamine to carry two peptides that simultaneously bind integrin αIIbβ3 and P-selectin on activated platelets to enhance the targeting of NPs to thrombus.

Results

The targeting specificity and binding stability of the NPs on red and white thrombi were demonstrated in vitro using a simulated circulatory device and the targeting effect of the NPs on mixed thrombus was studied by  magnetic resonance (MR)/photoacoustic (PA) dual-modality imaging in vivo. NPs that were surface modified with both peptides have higher selectivity and retention to red and white thrombi in vitro than NPs with a single or no peptide, and the targeting effect was closely related to the number and distribution of activated platelets as well as the structure and type of thrombus. The NPs also have MR/PA dual-modality imaging functionality, significantly enhancing the imaging of mixed thrombus in vivo.

Conclusion

These dual-targeted NPs have improved targeting specificity and binding stability to different thrombi under high shear stress and are beneficial for the early diagnosis of thrombosis.

Immobilization of the irreversible thrombin inhibitor D-Phe-Pro-Arg-chloromethylketone: a concept for hemocompatible surfaces?

The irreversible thrombin inhibitor D-Phe-Pro-Arg-chloromethylketone (PPACK) was covalently immobilized to PEGylated polymer thin films at its primary alpha-amino group. Activity assays and capture of radioconjugated thrombin reveal that the PPACK-decorated surfaces could bind thrombin forming up to 30% of a monolayer density. Back-calculation of this high thrombin-inhibiting capacity indicated that the surface immobilization of the inhibitor was still associated with more than two orders of magnitude of loss of activity; increasing activity was observed at higher surface densities. PPACK-containing polymer films almost duplicated the plasma coagulation time when compared with the reference substrate without inhibitor. In whole blood, however, the anticoagulant properties were below those previously found for benzamidine-type reversible thrombin inhibitors; in addition, the surface exhibited inflammatory properties. It is concluded that immobilized reversible thrombin inhibitors are more effective by passivating higher amounts of thrombin in a cooperative action with antithrombin III.

The protein C pathway in tissue inflammation and injury: pathogenic role and therapeutic implications

Inflammation and coagulation are closely linked interdependent processes. Under physiologic conditions, the tissue microcirculation functions in anticoagulant and anti-inflammatory fashions. However, when inflammation occurs, coagulation is also set in motion and actively participates in enhancing inflammation. Recently, novel and unexpected roles of hemostasis in the humoral and cellular components of innate immunity have been described. In particular, the protein C system, besides its well-recognized role in anticoagulation, plays a crucial role in inflammation. Indeed, the protein C system is now emerging as a novel participant in the pathogenesis of acute and chronic inflammatory diseases, such as sepsis, asthma, inflammatory bowel disease, atherosclerosis, and lung and heart inflammation, and may emerge as unexpected therapeutic targets for intervention.

The protein C pathway in tissue inflammation and injury: pathogenic role and therapeutic implications

Inflammation and coagulation are closely linked interdependent processes. Under physiologic conditions, the tissue microcirculation functions in anticoagulant and anti-inflammatory fashions. However, when inflammation occurs, coagulation is also set in motion and actively participates in enhancing inflammation. Recently, novel and unexpected roles of hemostasis in the humoral and cellular components of innate immunity have been described. In particular, the protein C system, besides its well-recognized role in anticoagulation, plays a crucial role in inflammation. Indeed, the protein C system is now emerging as a novel participant in the pathogenesis of acute and chronic inflammatory diseases, such as sepsis, asthma, inflammatory bowel disease, atherosclerosis, and lung and heart inflammation, and may emerge as unexpected therapeutic targets for intervention.

Human activated protein C variants in a rat model of arterial thrombosis

BACKGROUND

Activated protein C (APC) inhibits coagulation by degrading activated factor V (FVa) and factor VIII (FVIIIa), protein S (PS) functioning as a cofactor to APC.

METHODS

By mutagenesis of the vitamin K-dependent Gla domain of APC, we have recently created an APC variant having enhanced anticoagulant activity due to increased affinity for negatively charged phospholipid membranes. In the present study, the potential antithrombotic effects of this APC variant, and of a variant APC that is additionally mutated in the serine protease domain, have been evaluated in a blind randomized study in a rat model of arterial thrombosis. In this model, we have previously found the combination of bovine APC and PS to be highly antithrombotic. Four treatment groups each containing 10 rats were, in a blind random fashion, given intravenous bolus injections of wild-type or mutant variants of APC (0.8 mg/kg) together with human PS (0.6 mg/kg) or human PS (0.6 mg/kg) alone. A control group with 20 animals where given vehicle only.

RESULTS

A trend to increased patency rates was noted in a group receiving one of the APC variants, but it did not reach statistical significance.

CONCLUSION

In conclusion, administration of human APC variants having enhanced anticoagulant efficacy together with human PS in a rat model of arterial thrombosis did not give an efficient antithrombotic effect. The lack of effect may be due to species-specific differences between the human protein C system and the rat hemostatic system.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Antithrombotic and anticoagulant effects of wild type and Gla-domain mutated human activated protein C in rats

The antithrombotic and anticoagulant effects of recombinant wild type (WT) and mutated human activated protein C (hAPC) were investigated using a rat model of arterial thrombosis. Recent in vitro studies using human plasma have shown enhanced anticoagulant effects of hAPC by mutagenesis of either loop 148 in the serine protease domain or of the Gla domain. The Gla-domain mutant QGNSEDY-hAPC (= H10Q/S11G/S12N/D23S/Q32E/N33D/H44Y) was found to be particularly active as an anticoagulant. We now combined the two mutations to create the variant QGNSEDY-hAPC:B148 and investigated the in vivo effects of this variant as well as of QGNSEDY-hAPC and WT hAPC using a rat model of arterial thrombosis. In vitro clotting experiments using rat plasma demonstrated WT hAPC to be inefficient, whereas both mutant hAPC variants yielded distinct dose dependent anticoagulant effects. In the arterial injury model, a segment of the left common carotid artery was opened longitudinally. An endarterectomy was performed and the arteriotomy was closed, whereafter the vessel was reperfused and the patency rate determined after 31 min. Three treatment groups each containing 10 rats and a control group of 20 animals were in a blind random fashion given intravenous bolus injections of 0.8 mg/kg WT or mutant hAPC or vehicle only. The ex vivo clotting times of plasma drawn 3 min after the injections, as compared to baseline clotting times, were approximately doubled by QGNSEDY-hAPC and tripled by QGNSEDY-hAPC:B148 infusions, while WT APC had little effect. Compared to the control group, none of the hAPC preparations had significant antithrombotic effect or increased arteriotomy bleeding.

Decreased inflammation and improved survival with recombinant human activated protein C treatment in experimental acute pancreatitis

HYPOTHESIS

Drotrecogin alfa (activated), the pharmacologic form of activated protein C and the first Food and Drug Administration-approved drug for treatment of severe sepsis, is beneficial in experimental acute pancreatitis (AP).

DESIGN

Animal study.

SETTING

Laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Mild (intravenous cerulein) or severe (intravenous cerulein plus intraductal glycodeoxycholic acid) AP was induced in 72 rats, and coagulation evaluated. Rats with severe AP were randomized to treatment with drotrecogin alfa (activated), 100 microg/kg per hour, or isotonic sodium chloride.

MAIN OUTCOME MEASURES

Histologic scoring of pancreatic necrosis, inflammation of the pancreas and lung (measured by myeloperoxidase concentration), coagulation measures, and 24-hour survival.

RESULTS

Severe consumptive coagulopathy, hemoconcentration, and leukocytosis were observed 6 hours after induction of severe AP, but not in mild AP. Treatment of AP with drotrecogin did not worsen coagulation measures. Although the degree of pancreatic necrosis was comparable in treated and untreated animals with severe AP, drotrecogin significantly reduced myeloperoxidase levels in the pancreas (P = .009) and lungs (P = .03). The 24-hour survival in severe AP was markedly improved in animals treated with drotrecogin (86% vs 38%; P = .05).

CONCLUSIONS

Animals with severe AP have severe consumptive coagulopathy, but administration of drotrecogin alfa (activated), 100 microg/kg per hour, does not worsen coagulation abnormalities. Drotrecogin treatment reduces inflammation in the pancreas and lungs and significantly improves survival. These results encourage clinical investigation of drotrecogin in the treatment of severe AP.

Low-molecular-weight heparin (dalteparin) effectively prevents thrombosis in a rat model of deep arterial injury

Unfractionated heparin is often used to prevent thrombosis in microvascular surgery, but a major drawback of heparin therapy is increased bleeding. Low-molecular-weight heparins prevent venous thrombosis as effectively as heparin and have better bioavailability and a longer plasma half-life, which explains the increased use of low-molecular-weight heparins as substitutes for heparin in clinical practice. However, the ability of low-molecular-weight heparins to prevent arterial thrombosis has been debated. In this study, the authors compared the antithrombotic and antihemostatic effects of heparin and the low-molecular-weight heparin dalteparin in a rat model of arterial thrombosis. A segment of the left common carotid artery was isolated between vascular clamps and opened longitudinally. An endarterectomy was performed and the arteriotomy was closed with a running suture. The antithrombotic effect (vascular patency 31 minutes after reperfusion) and the surgical bleeding were measured. Groups of 10 rats were treated in a blind, random fashion with intravenous injection of one of the following substances 1 minute before clamp release. Three groups received a bolus of heparin (20, 60, or 180 IU anti-factor Xa/kg), three groups received dalteparin (60, 180, or 540 IU anti-factor Xa/kg), and one group was treated with vehicle (saline). Heparin 180 IU/kg produced a distinct antithrombotic effect compared with the control group (p = 0.03), but it also significantly increased the surgical bleeding to 2.0 g compared with 1.5 g in the control group (medians, p = 0.01). Dalteparin 180 and 540 IU/kg also produced a powerful antithrombotic effect (p = 0.01 and p = 0.03, respectively). In contrast to heparin, 180 IU/kg dalteparin did not increase the surgical bleeding (median, 1.5 g; p = 0.37 versus controls). Dalteparin 540 IU/kg increased the median surgical bleeding to 2.6 g (p = 0.06 versus controls). The nonsignificant difference may be explained by the great interindividual variation of surgical bleeding in the high-dose dalteparin group. Dalteparin prevented arterial thrombosis as effectively as unfractionated heparin. In contrast to heparin, dalteparin did not increase the surgical bleeding, which indicates that dalteparin instead of heparin can be used to prevent thrombosis in microvascular surgery.

Active site-inactivated factor VIIa prevents thrombosis without increased surgical bleeding: topical and intravenous administration in a rat model of deep arterial injury

PURPOSE

The primary event in the procoagulant response after vascular interventions is the tissue factor (TF)-factor VIIa complex formation, which occurs when TF is exposed to the circulating blood by the inflicted trauma. Human recombinant active site-inhibited coagulation factor VIIa (FFR-rFVIIa) binds well to TF but cannot initiate blood coagulation, and should thereby block thrombus formation. This hypothesis was tested with a rat model of arterial thrombosis.

METHODS

In a blinded randomized study, the antithrombotic and antihemostatic effects of FFR-rFVIIa and heparin were evaluated in a rat model of mechanical deep arterial injury. In one arm of the study, FFR-rFVIIa (0.2 mg in 150 microL) or vehicle alone was applied topically at the site of vascular injury. In the other arm, FFR-rFVIIa (4 mg/kg), heparin (1 mg/kg), or vehicle alone was injected intravenously.

RESULTS

FFR-rFVIIa produced a powerful antithrombotic effect after both topical and intravenous administrations (P =.02 and P =.005, respectively) without increasing the surgical bleeding. Heparin prevented thrombosis equally well as FFR-rFVIIa (P =.0007), but doubled the surgical bleeding compared with FFR-rFVIIa (P =.03) and controls (P =.008). In the topical study, the antithrombotic effect was achieved without altering parameters of plasma anticoagulation (prothrombin time and activated partial thromboplastin time) or producing detectable levels of FFR-rFVIIa in plasma.

CONCLUSION

In this model FFR-rFVIIa effectively inhibits thrombus formation without the expense of increased surgical bleeding, which indicates the potential of FFR-rFVIIa as an effective and safe strategy for prevention of thrombosis in reconstructive vascular surgery and various forms of percutaneous revascularization.

Analysis of 45 episodes of arterial occlusive disease in Japanese patients with congenital protein C deficiency

Hereditary protein C deficiency is associated with a predisposition to venous thrombosis. It is not clear whether the deficiency is involved in arterial occlusion. In the present study, we screened for protein C amidolytic activity in patients admitted to the National Cardiovascular Center Hospital, and we identified among them 43 probands and 51 relatives with heterozygous protein C deficiency. Among them, 34 patients with heterozygous protein C deficiency had manifested 45 episodes of arterial occlusive disease. Venous thrombotic diseases were less common. In the examination of whether protein C deficiency hastens arterial occlusion, we found a significant difference (p =0.02) in the age at onset of acute myocardial infarction between the patients with protein C deficiency (n=10; 49.4+/-14.8 years) and a group of patients with normal protein C levels (n=42; 60.5+/-10.6 years). Acute myocardial infarction occurred before 40 years of age in a significantly greater proportion of the patients with protein C deficiency (3:10, 30%) as compared with the controls (2:42, 5%) (chi2=5.9, p=0.015). At the onset of atherothrombotic cerebral infarction the patients with protein C deficiency were significantly (p=0.022) younger (n= 11; 57.4+/-12.8 years) than those with normal protein C levels (n=48; 64.6+/-10.1 years). Venous thrombosis was the most frequent clinical manifestation (21 of 31 episodes) in the patients with antithrombin III deficiency (n=26; 68% of the total), who were admitted to our hospital. Thus, our study suggests that congenital protein C deficiency contributes to earlier onset of arterial occlusive diseases, especially acute myocardial infarction, in Japanese subjects.

Antithrombotic and platelet activating effects of heparin in prevention of microarterial thrombosis

It has been proposed that the limited effectiveness of heparin in preventing arterial thrombosis may be caused by heparin-mediated platelet activation. The effect of heparin on platelets and thrombus formation in vivo was investigated using a microarterial model of thrombosis involving registration of labeled platelets. Three groups of six rabbits each were treated with either saline, standard heparin, or heparin with low affinity for antithrombin III (LA-heparin), which exhibits a low anticoagulant potential but has a molecular weight distribution similar to standard heparin. (Fifty to 70 percent of standard heparin consists of low-affinity material). The heparins were infused intravenously at doses of 1 mg/kg body weight, followed by maintenance injections. Platelet accumulation was significantly increased in the LA-heparin group compared with the saline group, demonstrating heparin-induced platelet activation in vivo. In contrast to a powerful anticoagulant response observed in rabbit plasma, the antithrombotic effect of standard heparin was expressed incompletely. (Only two of three of the treated vessels remained patent). This study demonstrates heparin-induced platelet activation in vivo in conditions of platelet-mediated thrombus formation. The observations are consistent with the concept of heparin-induced platelet activation as one of the mechanisms explaining the limited effects of heparin in preventing arterial thrombosis.

Prevention of experimental arterial thrombosis by topical administration of active site-inactivated factor VIIa

PURPOSE

In vivo, the coagulation pathway is triggered by formation of a high-affinity complex between the tissue factor of the injured vascular wall and the activated form of blood coagulation factor VII (VIIa). We used a rabbit model of arterial thrombosis to examine the antithrombotic effect of topically administered active site-inactivated recombinant human factor VIIa (VIIai), which binds to tissue factor but is unable to initiate coagulation.

METHODS

Segments of both central arteries of rabbits' ears were isolated between vascular clamps, followed by arteriotomies and deep-vessel wall trauma. In each rabbit, the injured vessel segments were superfused with either VIIai (0.5 mg in 200 microliters vehicle) or vehicle alone in a blinded random manner (n = 20). The vessels were then closed with running sutures and reperfused. The effect of intravenously infused VIIai (4 mg/kg) or vehicle was studied in a separate series.

RESULTS

The administration of VIIai increased patency rates from 40% and 30% in the vehicle group at 30 and 120 minutes after reperfusion, respectively, to 85% and 75% in the VIIai group (p = 0.008 and p = 0.004). No antihemostatic side effects occurred: median arteriotomy bleeding times were 2 minutes in the vehicle group and 1 1/2 minutes in the VIIai group (p = 1). By contrast, intravenous infusion of VIIai produced no antithrombotic effect.

CONCLUSIONS

We have shown that topical administration of VIIai at arterial trauma sites produces an antithrombotic effect without the expense of a hemostatic defect. This mode of treatment seems to be highly attractive in the prevention of thrombotic complications in surgery on blood vessels.