Blood coagulation at the site of microvascular injury: effects of low-dose aspirin

Safe and effective thrombolysis in free flap salvage: Intra-arterial urokinase infusion

Despite the high success rate in reconstruction using free tissue transfer, flap failure is often caused by microvascular thrombosis. In a small percentage of cases with complete flap loss, a salvage procedure is performed. In the present study, the effectiveness of intra-arterial urokinase infusion through the free flap tissue was investigated to develop a protocol to prevent thrombotic failure. The retrospective study evaluated the medical records of patients who underwent salvage procedure with intra-arterial urokinase infusion after reconstruction with free flap transfer between January 2013 and July 2019. Thrombolysis with urokinase infusion was administered as salvage treatment for patients who experienced flap compromise more than 24 hours after free flap surgery. Because of an external venous drainage through the resected vein, 100,000 IU of urokinase was infused into the arterial pedicle only into the flap circulation. A total of 16 patients was included in the present study. The mean time to re-exploration was 45.4 hours (range: 24-88 hours), and the mean quantity of infused urokinase was 69,688 IU (range: 30,000-100,000 IU). 5 cases presented with both arterial and venous thrombosis, while 10 cases had only venous thrombosis and 1 case had only arterial thrombosis; in a study of 16 patients undergoing flap surgery, 11 flaps were found to have survived completely, while 2 flaps experienced transient partial necrosis and 3 were lost despite salvage efforts. In other word, 81.3% (13 of 16) of flaps survived. Systemic complications, including gastrointestinal bleeding, hematemesis, and hemorrhagic stroke, were not observed. The free flap can be effectively and safely salvaged without systemic hemorrhagic complications using high-dose intra-arterial urokinase infusion within a short period of time without systemic circulation, even in delayed salvage cases. Urokinase infusion results in successful salvage and low rate of fat necrosis.

Platelet Inhibition by Low-Dose Acetylsalicylic Acid Reduces Neuroinflammation in an Animal Model of Multiple Sclerosis

Aside from the established immune-mediated etiology of multiple sclerosis (MS), compelling evidence implicates platelets as important players in disease pathogenesis. Specifically, numerous studies have highlighted that activated platelets promote the central nervous system (CNS)-directed adaptive immune response early in the disease course. Platelets, therefore, present a novel opportunity for modulating the neuroinflammatory process that characterizes MS. We hypothesized that the well-known antiplatelet agent acetylsalicylic acid (ASA) could inhibit neuroinflammation by affecting platelets if applied at low-dose and investigated its effect during experimental autoimmune encephalomyelitis (EAE) as a model to study MS. We found that oral administration of low-dose ASA alleviates symptoms of EAE accompanied by reduced inflammatory infiltrates and less extensive demyelination. Remarkably, the percentage of CNS-infiltrated CD4+ T cells, the major drivers of neuroinflammation, was decreased to 40.98 ± 3.28% in ASA-treated mice compared to 56.11 ± 1.46% in control animals at the disease maximum as revealed by flow cytometry. More interestingly, plasma levels of thromboxane A2 were decreased, while concentrations of platelet factor 4 and glycoprotein VI were not affected by low-dose ASA treatment. Overall, we demonstrate that low-dose ASA could ameliorate the platelet-dependent neuroinflammatory response in vivo, thus indicating a potential treatment approach for MS.

ImpaCt of aspirin regimen on THrombin generation in diabEtic patients with acute coronary syndrome: CARTHaGE-ACS trial

BACKGROUND

Diabetes is associated with a high rate of events after acute coronary syndrome. It was recently reported that once-daily aspirin might not provide stable biological efficacy in patients with diabetes.

AIMS

We sought to compare the biological efficacy of aspirin given once a day versus aspirin divided twice per day in a population of diabetic patients with non-ST elevation acute coronary syndrome (NSTE-ACS) as assessed by the thrombin generation test.

METHODS

We performed an open-label single-blind randomized study including 59 consecutive diabetic patients admitted for NSTE-ACS. Patients were randomly treated with aspirin 100 mg once a day (GA100; n = 20), aspirin 160 mg once a day (GA160; n = 19) or aspirin 100 mg twice a day (G2A100; n = 20). The primary endpoint was endogenous thrombin potential (ETP) at discharge and after 6 months.

RESULTS

The mean age of our patients was 61.5 ± 9 years, and 73% were male. The baseline characteristics were comparable between the three groups. In the GA100 group, there was no significant effect on ETP variation at 6 months (1150.46 ± 504.84 vs. 1087.63 ± 454.18; p = 0.794). An increase in aspirin dose with a second daily administration of 100 mg was associated with a significant reduction in ETP at 6 months (1004.87 ± 196.2 vs. 1233.63 ± 333.5; p = 0.003). A nonsignificant decrease in ETP was seen in the GA160 group (from 1173.8 ± 388.07 to 1053.64 ± 269.93 at 6 months, p = 0.117).

CONCLUSION

Only the twice-daily aspirin regimen led to better control of hypercoagulability in NSTE-ACS diabetic patients. However, no thrombin generation normalization was reported.

Combination Antiplatelet and Oral Anticoagulant Therapy in Patients With Coronary and Peripheral Artery Disease

Antiplatelet therapy is the mainstay for the treatment of acute and chronic arterial disease involving the coronary and peripheral beds. However, questions remain about optimal antithrombotic therapy for long-term treatment of chronic vascular disease. The observation that dual antiplatelet therapy with acetylsalicylic acid and clopidogrel was associated with lower thrombotic event rates than acetylsalicylic acid monotherapy in patients with acute coronary syndromes and those undergoing percutaneous coronary intervention changed the treatment paradigm. Moreover, the demonstration that more pharmacodynamically potent P2Y₁₂ inhibitors than clopidogrel were associated with fewer thrombotic event occurrences further solidified the dual antiplatelet therapy approach. However, recurrent thrombotic events occur in ≈1 in 10 patients in the first year following an acute coronary syndrome event, despite treatment with the most potent P2Y₁₂ inhibitors, a limitation that has stimulated interest in exploring the efficacy and safety of approaches using anticoagulants on top of antiplatelet therapy. These investigations have included treatment with very-low-dose oral anticoagulation, and even its replacement of acetylsalicylic acid in the presence of a P2Y₁₂ inhibitor, in patients stabilized after an acute coronary syndrome event. Recent basic and translational studies have suggested noncanonical effects of coagulation factor inhibition that may further modulate clinical benefits. This in-depth review will discuss developments in our understanding of the roles that platelets and coagulation factors play in atherothrombosis and review the rationale and clinical evidence for combining antiplatelet and oral anticoagulant therapy in patients with coronary and peripheral artery disease.

Plasma Fibrin Clot Properties as Determinants of Bleeding Time in Human Subjects: Association with Histidine-Rich Glycoprotein

Aims

Fibrin formation and histidine-rich glycoprotein (HRG) are involved in primary hemostasis and wound healing. Little is known regarding the relationship of clot characteristics, bleeding time, and wound healing.

Methods and Results

We studied 154 patients with coronary artery disease (CAD) and 154 subjects free of CAD matched for age, obesity, and current smoking. We evaluated bleeding time (BT) using standardized skin incisions on a forearm, along with plasma clot permeability (K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower p < 0.001). After adjusting for potential confounders, K_s), clot lysis time (CLT), and histidine-rich glycoprotein (HRG). Compared with controls, BT was 45% shorter in CAD cases. CAD patients had 32% lower n = 79, 25.6%) was independently predicted by both short and prolonged BT in CAD cases (OR 21.87, 95% CI 7.41-64.55 and OR 10.17, 95% CI 2.88-35.97) and controls (OR 5.94, 95% CI 2.29-15.41 and OR 14.76, 95% CI 4.29-50.77, respectively).

Conclusions

The study shows that plasma fibrin clot density and HRG may influence BT and that appropriate skin wound healing is associated with medium BT. Translational Perspective. Elucidation of the complex relationships between plasma fibrin clot phenotype and wound healing might have important practical implications.

Bismuth Subsalicylate Coagulopathy in a Patient with Chronic Liver Disease

Bismuth subsalicylate (BSS) is the active ingredient in over-the-counter antacid and antidiarrheal medications. Coagulopathy in the setting of acetylsalicylic acid toxicity is well documented but not in setting of bismuth subsalicylate overuse. We present a case report of coagulopathy from BSS poisoning in a patient with underlying cirrhosis. The patient's high prothrombin time suggests inhibition of vitamin K-dependent coagulation factors. The patient had decreased factor V activity, which is responsible for converting prothrombin to thrombin. Patients with cirrhosis often have hypoprothrombinemia which may be exacerbated by salicylate-induced coagulopathy. Given the widespread use of BSS products, physicians should recognize coagulopathy as a possible manifestation of toxicity especially in patients with underlying liver disease.

Appropriate Use of Intravenous Unfractionated Heparin after Digital Replantation: A Randomized Controlled Trial Involving Three Groups

BACKGROUND

The purpose of this study was to clarify the appropriate use of unfractionated heparin as an anticoagulation agent after digital replantation.

METHODS

This study was a prospective, randomized, single-blind, blinded-endpoint method, three-arm, parallel-group, controlled clinical trial conducted at a single institution. A total of 88 patients (101 fingers) following digital amputation and subsequent repair by anastomosis of both arteries and veins were randomly allocated into three groups: (1) control group (no heparin dose), (2) low-dose heparin group (10,000 IU/day), and (3) high-dose heparin group (start at 15,000 IU/day, then adjust the dose to achieve an activated partial thromboplastin time of 1.5 to 2.5 times the baseline). The outcomes were assessed regarding the proportion of success at 2 weeks after replantation of amputated digits, total or partial necrosis, and occurrence of complications.

RESULTS

No significant differences were found among the three groups, except for complications of congestion. The odds ratio of the heparin group compared with the control group for a success proportion was 5.40 (95 percent CI, 0.85 to 34.20; p = 0.027) in subjects aged 50 years or older. Significant elevations of activated partial thromboplastin time, aspartate transaminase, and alanine aminotransferase occurred in high-dose heparin groups on day 7.

CONCLUSION

Unfractionated heparin administration is considered effective for patients aged 50 years or older, although the routine use of unfractionated heparin is not necessary after digital replantation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Use of thrombin generation test for monitoring hemostasis in coronary bypass surgery

To evaluate the parameters of the thrombin generation test (TGT) in coronary artery disease (CAD) patients on prolonged aspirin therapy during on-pump coronary artery bypass grafting (CABG) after donor platelet concentrate transfusion. A total of 148 patients with CAD on prolonged aspirin therapy (75–100 mg/day) who have undergone elective on-pump CABG were consecutively included in the study. Patients were divided randomly into two groups. Group 1 (n = 76) received donor platelet transfusions after cardiopulmonary bypass, whereas Group 2 (n = 72) did not. TGT parameters were measured using an analyzer at pre-, intra-, and early postoperative periods. Activation of the endogenous thrombin potential was observed in patients on prolonged aspirin therapy in the pre- and intraoperative periods, as confirmed by high peak thrombin and increased velocity index. The activation time of the prothrombinase complex and thrombin generation time were greater than the control group. The blood hemostatic potential in patients who did not receive transfusions in the early postoperative period decreased up to the level of the control group in the extended time parameters. Hemostatic potential in plasma in patients on aspirin was preserved. Given the laboratory test results and clinical data, platelet concentrate transfusion is unnecessary for prevention.

Aspirin and the prevention of venous thromboembolism following total joint arthroplasty: commonly asked questions

The number of arthroplasties being performed increases each year. Patients undergoing an arthroplasty are at risk of venous thromboembolism (VTE) and appropriate prophylaxis has been recommended. However, the optimal protocol and the best agent to minimise VTE under these circumstances are not known. Although many agents may be used, there is a difference in their efficacy and the risk of bleeding. Thus, the selection of a particular agent relies on the balance between the desire to minimise VTE and the attempt to reduce the risk of bleeding, with its undesirable, and occasionally fatal, consequences.

Acetylsalicylic acid (aspirin) is an agent for VTE prophylaxis following arthroplasty. Many studies have shown its efficacy in minimising VTE under these circumstances. It is inexpensive and well-tolerated, and its use does not require routine blood tests. It is also a ‘milder’ agent and unlikely to result in haematoma formation, which may increase both the risk of infection and the need for further surgery. Aspirin is also unlikely to result in persistent wound drainage, which has been shown to be associated with the use of agents such as low-molecular-weight heparin (LMWH) and other more aggressive agents.

The main objective of this review was to summarise the current evidence relating to the efficacy of aspirin as a VTE prophylaxis following arthroplasty, and to address some of the common questions about its use.

There is convincing evidence that, taking all factors into account, aspirin is an effective, inexpensive, and safe form of VTE following arthroplasty in patients without a major risk factor for VTE, such as previous VTE.

Cite this article: Bone Joint J 2017;99-B:1420–30.

Capillary Flow Rates in the Duodenum of Pediatric Ulcerative Colitis Patients Are Increased and Unrelated to Inflammation

BACKGROUND AND AIM

Inflammatory bowel diseases (IBD), including Crohn disease (CD) and ulcerative colitis (UC), are chronic pediatric disorders. Changes in vasculature are described in IBD, but these could be secondary to inflammation and the role in pathogenesis is poorly understood. Assessing circulatory changes in typically unaffected sites in IBD (eg, duodenum), when inflammation is absent, can identify vascular changes associated with pathogenesis. The aim of the study is to measure capillary flow rates in duodenal mucosa using probe-based confocal laser endomicroscopy (pCLE) during endoscopy in children with IBD.

METHODS

Images of villi with visible blood vessels obtained using pCLE were captured as video sequences. Capillary flow rate (mm/s) was calculated by dividing the distance travelled by blood cells by the duration of the sequence. Flow rates were correlated with various clinical parameters.

RESULTS

Forty-five patients (22 non-IBD, 14 CD, 9 UC) were included in the study. Duodenal capillary flow rates were significantly higher in UC patients (0.75 ± 0.07 mm/s) as compared to non-IBD (0.57 ± 0.03) and CD (0.65 ± 0.04). There was no correlation between serum hemoglobin and albumin, disease activity indices, serum inflammatory markers, and capillary flow rates in patients.

CONCLUSIONS

This pilot study shows, for the first time, increased capillary blood flow in the duodenum of UC patients that was unrelated to inflammatory markers or disease activity. Thus, early vascular changes can be assessed using pCLE during endoscopy.

SerpinC1/Antithrombin III in kidney-related diseases

The gene SerpinC1 encodes a serine protease inhibitor named antithrombin III (ATIII). This protease demonstrates both anticoagulant and anti-inflammatory action. ATIII is the most important coagulation factor inhibitor, and even minor changes in ATIII can significantly alter the risk of thromboembolism. ATIII can also suppress inflammation via a coagulation-dependent or -independent effect. Moreover, apart from ATIII deficiency, ATIII and its gene SerpinC1 may also be related to many diseases (e.g. hypertension, kidney diseases). The present review summarizes how ATIII affects the progress of kidney disease and its mechanism. Further studies are required to investigate how ATIII affects renal function and the treatment.

The effect of a dual or a triple antithrombotic therapy with apixaban on thrombus formation in vivo and in an ex vivo perfusion chamber model: An open-label, controlled, sequential study

BACKGROUND

There is a need to optimize pharmacological treatment in patients with acute coronary syndrome and concomitant atrial fibrillation, in particular with newer antithrombotic medicines. We have therefore studied if dual or triple combination of antithrombotic agents exert similar effects on coagulation activation in an in vivo model in the skin microvasculature and in an ex vivo perfusion chamber.

METHODS AND RESULTS

Shed blood platelet activation (β-thromboglobulin [β-TG]), thrombin generation (thrombin-antithrombin complex [TAT]) and volume as well as markers of thrombus size (D-dimer) and its platelet content (P-selectin) in a perfusion chamber were studied in a sequential, open-label, parallel group trial in 40 healthy male volunteers (n = 20 per group). Subjects received ticagrelor and apixaban without or with acetylsalicylic acid (ASA). Outcome parameters were assessed at 3 hours after therapy dosing, and at steady-state trough and peak conditions.A triple or dual therapy induced a comparable decrease in shed blood β-TG at 3 hours after therapy dosing but was more pronounced at steady-state conditions with the more intense treatment combination. During both antithrombotic regimens a similarly sustained inhibition in thrombin generation was observed which was accompanied by comparable increases in shed blood volume. In contrast, no treatment effect could be observed in the perfusion chamber experiment.

CONCLUSION

Ticagrelor and apixaban with or without ASA inhibit platelet activation and thrombin formation in vivo in healthy subjects. Platelet inhibition was greater at steady-state conditions after triple therapy administration.

Effects of anticoagulation on markers of activation of clotting following major orthopedic surgery

INTRODUCTION

This study examines makers of activation of clotting following three chemoprophylactic regimens used for prevention of postoperative venous thromboembolic disease (TED) following high-risk surgery for TED.

METHODS

Patients having elective primary knee or hip replacement surgery received variable dose warfarin (target international normalized ratios 2.0-2.5), 1 mg warfarin daily starting 7 days preoperatively or aspirin 325 mg daily starting on the day of surgery. Twelve patients in each group were treated for 28 ± 2 days. Thrombin-antithrombin (T-AT) and prothrombin fragment F1 + 2 were measured at baseline and postoperative days 3 and 28 ± 2.

RESULTS

Thrombin-antithrombin and F1 + 2 on postoperative day 3 were equal for the study groups. By days 28 ± 2, variable dose warfarin therapy group suppressed production of F1 + 2 (P = 0.002) with no difference in the T-AT accumulation. F1 + 2 for other patients overlapped the normal range.

CONCLUSION

The signals of activated clotting following surgery did not differentiate the three regimens on postoperative day 3. Variable dose warfarin was associated with suppression of F1 + 2 after 1 month of therapy, with no effect on accumulation of T-AT. Fixed low-dose warfarin started 7 days prior to surgery and aspirin are not inferior on postoperative day 3, but appear to be inferior over a longer treatment.

Trypsin, Tryptase, and Thrombin Polarize Macrophages towards a Pro-Fibrotic M2a Phenotype

For both wound healing and the formation of a fibrotic lesion, circulating monocytes enter the tissue and differentiate into fibroblast-like cells called fibrocytes and pro-fibrotic M2a macrophages, which together with fibroblasts form scar tissue. Monocytes can also differentiate into classically activated M1 macrophages and alternatively activated M2 macrophages. The proteases thrombin, which is activated during blood clotting, and tryptase, which is released by activated mast cells, potentiate fibroblast proliferation and fibrocyte differentiation, but their effect on macrophages is unknown. Here we report that thrombin, tryptase, and the protease trypsin bias human macrophage differentiation towards a pro-fibrotic M2a phenotype expressing high levels of galectin-3 from unpolarized monocytes, or from M1 and M2 macrophages, and that these effects appear to operate through protease-activated receptors. These results suggest that proteases can initiate scar tissue formation by affecting fibroblasts, fibrocytes, and macrophages.

Aspirin and multiple sclerosis

Aspirin is widely used to lessen the risks of cardiovascular events. Some studies suggest that patients with multiple sclerosis have an increased risk for some cardiovascular events, for example, venous thromboembolism and perhaps ischemic strokes, raising the possibility that aspirin could lessen these increased risks in this population or subgroups (patients with limited mobility and/or antiphospholipid antibodies). However, aspirin causes a small increased risk of hemorrhagic stroke, which is a concern as it could potentially worsen a compromised blood-brain barrier. Aspirin has the potential to ameliorate the disease process in multiple sclerosis (for example, by limiting some components of inflammation), but aspirin also has the potential to inhibit mitochondrial complex I activity, which is already reduced in multiple sclerosis. In an experimental setting of a cerebral ischemic lesion, aspirin promoted the proliferation and/or differentiation of oligodendrocyte precursors, raising the possibility that aspirin could facilitate remyelination efforts in multiple sclerosis. Other actions by aspirin may lead to small improvements of some symptoms (for example, lessening fatigue). Here we consider potential benefits and risks of aspirin usage by patients with multiple sclerosis.

A brief exposure to tryptase or thrombin potentiates fibrocyte differentiation in the presence of serum or serum amyloid p

A key question in both wound healing and fibrosis is the trigger for the initial formation of scar tissue. To help form scar tissue, circulating monocytes enter the tissue and differentiate into fibroblast-like cells called fibrocytes, but fibrocyte differentiation is strongly inhibited by the plasma protein serum amyloid P (SAP), and healthy tissues contain very few fibrocytes. In wounds and fibrotic lesions, mast cells degranulate to release tryptase, and thrombin mediates blood clotting in early wounds. Tryptase and thrombin are upregulated in wound healing and fibrotic lesions, and inhibition of these proteases attenuates fibrosis. We report that tryptase and thrombin potentiate human fibrocyte differentiation at biologically relevant concentrations and exposure times, even in the presence of concentrations of serum and SAP that normally completely inhibit fibrocyte differentiation. Fibrocyte potentiation by thrombin and tryptase is mediated by protease-activated receptors 1 and 2, respectively. Together, these results suggest that tryptase and thrombin may be an initial trigger to override SAP inhibition of fibrocyte differentiation to initiate scar tissue formation.

Antithrombotic triple therapy and coagulation activation at the site of thrombus formation: a randomized trial in healthy subjects

BACKGROUND

Patients with acute coronary syndrome and concomitant atrial fibrillation may require antithrombotic triple therapy but clinical evidence of safety and efficacy is poor. We have therefore studied the combination of different antithrombotic medicines for coagulation activation in an in vivo model in the skin microvasculature.

METHODS AND RESULTS

Platelet activation (β-thromboglobulin [β-TG]) and thrombin generation (prothrombin fragment 1 + 2 [F1+2 ], thrombin-antithrombin complex [TAT]) were studied in an open-label, randomized, parallel group trial in 60 healthy male subjects (n = 20 per group) who received ticagrelor and acetylsalicylic acid (ASA) in combination with dabigatran (150 mg bid), rivaroxaban (20 mg od) or phenprocoumon (INR 2.0-3.0). Coagulation biomarkers in shed blood were assessed at 3 h after monotherapy with the medicines under study, at 3 h after triple therapy dosing and at steady state trough conditions. Single doses of ticagrelor, dabigatran or rivaroxaban caused comparable decreases in shed blood β-TG and were more pronounced than phenprocoumon at an INR of 2.0-3.0. In contrast, thrombin generation was more affected by rivaroxaban and phenprocoumon than by dabigatran. During triple therapy a similarly sustained inhibition of platelet activation and thrombin generation with a maximum decrease of β-TG, F1+2 and TAT at 3 h post-dosing was noted, which remained below pre-dose levels at trough steady state.

CONCLUSION

A triple therapy at steady state with ticagrelor plus ASA in combination with dabigatran or rivaroxaban is as effective as a combination with phenprocoumon for platelet activation and thrombin generation in vivo.

Why does aspirin decrease the risk of venous thromboembolism? On old and novel antithrombotic effects of acetyl salicylic acid

It is well established that aspirin, an irreversible inhibitor of platelet cyclooxygenase activity, is effective in secondary prevention of arterial thromboembolic events. The pooled results of the recent randomized, multicenter WARFASA and ASPIRE aspirin trials showed a 32% reduction in the rate of recurrence of venous thromboembolism (VTE) in patients receiving aspirin following VTE. These clinical data support evidence that platelets contribute to the initiation and progression of venous thrombosis and aspirin inhibits thrombin formation and thrombin-mediated coagulant reactions. In addition to the known acetylation of serine 529 residue in platelet cyclooxygenase-1, the postulated mechanisms of aspirin-induced antithrombotic actions also involve the acetylation of other proteins in blood coagulation, including fibrinogen, resulting in more efficient fibrinolysis. This review summarizes current knowledge on the aspirin-induced antithrombotic effects that potentially explain clinical studies showing reduced rates of VTE events in aspirin-treated subjects.

Anticoagulant effects of statins and their clinical implications

There is evidence indicating that statins (3-hydroxy-methylglutaryl coenzyme A reductase inhibitors) may produce several cholesterol-independent antithrombotic effects. In this review, we provide an update on the current understanding of the interactions between statins and blood coagulation and their potential relevance to the prevention of venous thromboembolism (VTE). Anticoagulant properties of statins reported in experimental and clinical studies involve decreased tissue factor expression resulting in reduced thrombin generation and attenuation of pro-coagulant reactions catalysed by thrombin, such as fibrinogen cleavage, factor V and factor XIII activation, as well as enhanced endothelial thrombomodulin expression, resulting in increased protein C activation and factor Va inactivation. Observational studies and one randomized trial have shown reduced VTE risk in subjects receiving statins, although their findings still generate much controversy and suggest that the most potent statin rosuvastatin exerts the largest effect.

Primary and secondary prevention of cardiovascular disease in diabetes with aspirin

Diabetes is associated with an increased cardiovascular risk. The role for aspirin in diabetes is of high clinical interest. Guidelines recommend that primary prevention of cardiovascular disease (CVD) in diabetes with aspirin should be based on the individual risk for CVD. New mechanistic studies suggest that enhanced platelet turnover may partly contribute to the fact the primary prevention studies found unequivocal results in diabetes. There is initial evidence that a potential future modification of dosages in diabetes may counteract the enhancement in platelet turnover in diabetes. The use of aspirin in diabetic patients for secondary prevention of CVD is supported by key evidence. The aim of the review is to present recent studies on aspirin for prevention of CVD in diabetes and to highlight its role also in view of new mechanistic and clinical studies with aspirin. Novel aspects of aspirin, e.g. its potential role for the prevention of cancer, are also presented.

Reduced thrombin formation and altered fibrin clot properties induced by polyunsaturated omega-3 fatty acids on top of dual antiplatelet therapy in patients undergoing percutaneous coronary intervention (OMEGA-PCI clot)

OBJECTIVE

The goal of this study was to investigate whether omega-3 polyunsaturated fatty acids (n-3 PUFA) are able to alter plasma fibrin clot properties and reduce thrombin formation in stable coronary artery disease patients undergoing percutaneous coronary intervention (PCI).

METHODS AND RESULTS

In an investigator-initiated, prospective, double-blind, placebo-controlled, randomized study, patients undergoing PCI who received standard pharmacotherapy were assigned to the treatment with 1 g/day n-3 PUFA (n = 30) or placebo (n = 24) for 1 month. Plasma fibrin clot permeability (K(s)); lysis time (t(50%)); prothrombin fragment 1.2; and peak thrombin generation from automated thrombogram, 8-isoprostaglandin F(2α) (8-iso-PGF(2α), an oxidative stress marker), and C-reactive protein were determined at baseline, 3 to 5 days after randomization, and 30 days after randomization. At baseline, both treatment groups did not differ significantly. A 1-month treatment with n-3 PUFA compared with placebo was associated with 15.3% higher K(s), indicating larger pores in the fibrin network (P = 0.0005); 14.3% shorter t(50%), indicating increased susceptibility to fibrinolysis (P<0.0001); 33.8% lower prothrombin fragment 1.2 (P = 0.0013); 13.4% lower peak thrombin generation (P = 0.04); and 13.1% lower 8-iso-PGF(2α) (P = 0.009). Treatment with n-3 PUFA had no effect on fibrinogen and C-reactive protein. After 1 month of treatment, fibrinogen (r = -0.53, P<0.0001), treatment assignment (r = 0.29, P = 0.006) and 8-iso-PGF(2α) (r = -0.27, P = 0.015) were independently associated with clot permeability (P<0.0001, R(2) = 0.66).

CONCLUSIONS

Adding n-3 PUFA to standard therapy in stable patients undergoing PCI significantly decreases thrombin formation and oxidative stress and favorably alters fibrin clot properties. These findings indicate novel antithrombotic effects induced by n-3 PUFA in humans.

Prothrombin activation on the activated platelet surface optimizes expression of procoagulant activity

Effective hemostasis relies on the timely formation of α-thrombin via prothrombinase, a Ca(2+)-dependent complex of factors Va and Xa assembled on the activated platelet surface, which cleaves prothrombin at Arg271 and Arg320. Whereas initial cleavage at Arg271 generates the inactive intermediate prethrombin-2, initial cleavage at Arg320 generates the enzymatically active intermediate meizothrombin. To determine which of these intermediates is formed when prothrombin is processed on the activated platelet surface, the cleavage of prothrombin, and prothrombin mutants lacking either one of the cleavage sites, was monitored on the surface of either thrombin- or collagen-activated platelets. Regardless of the agonist used, prothrombin was initially cleaved at Arg271 generating prethrombin-2, with α-thrombin formation quickly after via cleavage at Arg320. The pathway used was independent of the source of factor Va (plasma- or platelet-derived) and was unaffected by soluble components of the platelet releasate. When both cleavage sites are presented within the same substrate molecule, Arg271 effectively competes against Arg320 (with an apparent IC(50) = 0.3μM), such that more than 90% to 95% of the initial cleavage occurs at Arg271. We hypothesize that use of the prethrombin-2 pathway serves to optimize the procoagulant activity expressed by activated platelets, by limiting the anticoagulant functions of the alternate intermediate, meizothrombin.

Simvastatin administration reduces thromboxane production in subjects taking aspirin: links between aspirin resistance and thrombin generation

BACKGROUND

Growing evidence indicates that statins may reduce thromboxane A(2) synthesis and thrombin generation. We investigated the relationships between thromboxane production, thrombin generation, and oxidative stress in patients receiving aspirin before and after statin administration.

METHODS

An open-label study was conducted in 112 men, aged 54.4 ± 7.3 years, at an increased cardiovascular risk receiving aspirin (75 mg/d). Prior to and following a 3-month simvastatin treatment (40 mg/d), we evaluated circulating thromboxane B(2) (TXB(2)), inflammatory markers, 8-isoprostane, and prothrombin fragment 1.2 (F1.2), a marker of thrombin generation, which was also measured in blood collected every 60s at the site of standardized skin incisions.

RESULTS

Subjects (n=28) with pretreatment TXB(2) concentrations in the highest quartile ("aspirin-resistant patients") were more frequently current smokers and had elevated C-reactive protein (CRP), interleukin-6, 8-isoprostane, shorter bleeding time, and increased F1.2 production in a model of microvascular injury, when compared with the 3 remaining quartiles (all, p<0.001). Simvastatin decreased serum TXB(2) in the whole group (by 20%, p=0.0008). Patients in the highest quartile of the baseline TXB(2) had still higher posttreatment TXB(2), CRP, interleukin-6, and F1.2 formation following injury (all, p<0.001). Simvastatin-induced change in TXB(2) correlated with the magnitude of changes in maximum levels and the velocity of F1.2 formation (all p<0.001) but not with changes in inflammatory markers or lipid profile.

CONCLUSIONS

The study shows that statins significantly reduce platelet TXA(2) formation in patients taking low-dose aspirin and this effect is associated with attenuated thrombin formation in response to vascular injury.

Low dose acetylsalicylic acid and shedding of microparticles in vivo in humans

BACKGROUND

Microparticles (MPs) have procoagulant properties as shown in vitro and in animal models. Their role in haemostatic system activation at the site of a vascular injury in vivo in humans has not been studied.

MATERIAL AND METHODS

In a prospective randomized crossover study, 13 healthy volunteers were given 100 mg acetylsalicylic acid or placebo daily for 7 days. Number and cellular origin, expression of tissue factor (TF) and phosphatidylserine on MPs, and platelet and coagulation activation markers [beta-thromboglobulin (beta-TG), prothrombin fragment f1.2 (f1.2)] were measured in venous blood and in blood from a vascular injury (shed blood) by flow cytometry and immunoassays, respectively.

RESULTS

The number of MPs was significantly higher in shed blood than in venous blood. The majority of MPs were platelet derived. The expression of TF on MPs was low, but higher in shed blood than in venous blood. TF positive MPs were significantly higher in shed blood, which was due to an increase of MPs from platelets (PMPs). In shed blood, the number of TF expressing platelet-derived MPs correlated with beta-TG, but not with f1.2. Low dose acetylsalicylic acid did not affect shedding of PMPs, neither in venous blood nor in shed blood.

CONCLUSIONS

The release of PMPs locally at the site of platelet plug formation in humans indicates a possible role of MPs for haemostatic system activation in vivo. Low dose acetylsalicylic acid might not be strong enough to suppress shedding of PMPs in the microcirculation.

Ex Vivo Thrombin Generation in Patients With Venous Thromboembolic Disease or Atrial Fibrillation on Long-Term Oral Anticoagulation

International normalized ratio (INR) is used to monitor chronic oral anticoagulant (OA) treatment; however, it is poorly understood how this simple test reflects in vivo hemostatic reactions, culminating in thrombin generation and clot formation. We studied the process of thrombin generation using an ex vivo model, where thrombin—antithrombin (TAT) complexes are measured in blood emerging from standardized skin incisions in 55 patients (35 with venous thromboembolism [VTE] and 20 with sustained atrial fibrillation [AF]) treated with acenocoumarol (INR 2.0-3.0). In addition, in venous blood, we measured the activity of factor VIII (FVIII) and vitamin K-dependent coagulation proteins. Chronic anticoagulation led to significant reductions in maximum TAT concentrations as compared to 35 healthy controls, in maximum TAT generation rates, and in mean amount of thrombin generated. Parameters of thrombin generation did not correlate with INR or any coagulation factor measured. International normalized ratio was significantly and independently affected by the decrease in the activity of all vitamin K-dependent coagulation proteins. The strongest influence was shown for FVII. Factor VIII activity was increased in all patients studied independently of the duration of anticoagulation and did not change over time. In conclusion, in patients with VTE and AF on OA, there is no correlation between INR values and parameters of ex vivo thrombin generation. This may indicate an important role of protein C (PC) system and possibly other endothelium-dependent mechanisms in controlling hemostasis. Increased FVIII activity in patients with VTE and AF does not change significantly during anticoagulation and is probably related to the pretreatment prothrombotic state.

A randomized clinical trial investigating the relationship between aprotinin and hypercoagulability in off-pump coronary surgery

BACKGROUND

Off-pump coronary artery bypass (OPCAB) surgery is associated with a hypercoagulable state in which the platelet thrombin receptor, protease-activated receptor-1 (PAR-1), helps propagate a thrombin burst within saphenous vein grafts. Aprotinin, used in cardiothoracic surgery mainly for its antifibrinolytic properties, also spares platelet PAR-1 activation due to thrombin. We hypothesized that this PAR-1 antagonistic property provides an antithrombotic benefit during OPCAB surgery.

METHODS

Patients were randomly assigned to receive saline (n = 38) or a modified full-dose regimen of aprotinin (n = 37) IV during OPCAB surgery. Blood sampled perioperatively from the coronary sinus, skin wounds, and systemic circulation was analyzed to test coagulation and platelet function. Major adverse cardiovascular events were monitored by obtaining troponin I at 24 h (myocardial infarction), predischarge computed tomography angiography (vein graft thrombosis), and by clinical examination for stroke.

RESULTS

Coronary sinus blood obtained immediately after OPCAB surgery showed significantly less activation in the aprotinin group, as judged by reduced formation of platelet-leukocyte conjugates (P < 0.02) and platelet-derived microparticles (P < 0.05). The aprotinin group showed inhibition of platelet aggregation induced by thrombin (P = 0.007) but not adenosine diphosphate. Thrombin generation, defined by F1.2 levels, was significantly reduced by aprotinin in the coronary sinus but not in skin wound incisions. Major adverse cardiovascular events were significantly reduced in aprotinin-treated patients (5.4% vs 29.7%, P < 0.05). Aprotinin also demonstrated antifibrinolytic properties through diminished red blood cell transfusion (P < 0.04) and reduced blood loss postoperatively (603 +/- 330 vs 810 +/- 415 mL, P < 0.004).

CONCLUSION

This study demonstrates that aprotinin protects patients undergoing OPCAB surgery from a hypercoagulable state by diminishing thrombin-induced platelet activation and thrombin generation within saphenous vein grafts, while maintaining systemic hemostatic and antifibrinolytic benefits. These results support further investigation of aprotinin and other PAR-1 antagonists in OPCAB surgery.

Systemic blood coagulation activation in acute coronary syndromes

We evaluated systemic alterations to the blood coagulation system that occur during a coronary thrombotic event. Peripheral blood coagulation in patients with acute coronary thrombosis was compared with that in people with stable coronary artery disease (CAD). Blood coagulation and platelet activation at the microvascular injury site were assessed using immunochemistry in 28 non-anticoagulated patients with acute myocardial infarction (AMI) versus 28 stable CAD patients matched for age, sex, risk factors, and medications. AMI was associated with increased maximum rates of thrombin-antithrombin complex generation (by 93.8%; P< .001), thrombin B-chain formation (by 57.1%; P< .001), prothrombin consumption (by 27.9%; P= .012), fibrinogen consumption (by 27.0%; P= .02), factor (f) Va light chain generation (by 44.2%; P= .003), and accelerated fVa inactivation (by 76.1%; P< .001), and with enhanced release of platelet-derived soluble CD40 ligand (by 44.4%; P< .001). FVa heavy chain availability was similar in both groups because of enhanced formation and activated protein C (APC)-mediated destruction. The velocity of coagulant reactions in AMI patients showed positive correlations with interleukin-6. Heparin treatment led to dampening of coagulant reactions with profiles similar to those for stable CAD. AMI-induced systemic activation of blood coagulation markedly modifies the pattern of coagulant reactions at the site of injury in peripheral vessels compared with that in stable CAD patients.

Tissue factor +5466A>G polymorphism determines thrombin formation following vascular injury and thrombin-lowering effects of simvastatin in patients with ischemic heart disease

OBJECTIVE

We examined the hypothesis that the +5466A>G variant (rs3917643) of the tissue factor (TF) gene is associated with thrombin formation following simvastatin in patients with ischemic heart disease (IHD).

METHODS AND RESULTS

Prothrombin 1.2 fragments (F1.2) and thrombin-antithrombin complexes (TAT) were assessed in 95 men with stable IHD, aged 54.4+/-6.8 years, in blood collected every 60s from the bleeding-time wounds before and after a 3-month simvastatin administration (40 mg/day). We identified 16 patients with the TF +5466AG genotype and 79 subjects with the +5466AA genotype. Baseline maximum rates of F1.2 and TAT formation and their maximum levels at the site of vascular injury, but not in venous blood, were higher in +5466G allele carriers than in those with +5466AA genotype (P<0.0001). The magnitude of reduction in maximum rates of F1.2 and TAT formation following simvastatin was larger (P<0.001) in +5466G allele carriers than in +5466AA subjects. The degree of decrease in maximum local levels of F1.2 and TAT after simvastatin was similar in both genotype groups. The presence of the +5466G allele was independently associated with the maximum velocity of F1.2 and TAT generation and maximum levels of both markers before and after simvastatin in multiple regression models (P<0.01 for all analyses). Local thrombin generation, in +5466AG and +5466AA subjects, showed no significant correlations with lipid variables.

CONCLUSIONS

Thrombin formation following vascular injury and thrombin-lowering effect of statins in patients with IHD are at least in part genetically determined by the TF +5466A>G polymorphism.

Hyperglycemia is associated with enhanced thrombin formation, platelet activation, and fibrin clot resistance to lysis in patients with acute coronary syndrome

OBJECTIVE

Acute hyperglycemia on admission for acute coronary syndrome worsens the prognosis in patients with and without known diabetes. Postulated mechanisms of this observation include prothrombotic effects. The aim of this study was to evaluate the effect of elevated glucose levels on blood clotting in acute coronary syndrome patients.

RESEARCH DESIGN AND METHODS

We studied 60 acute coronary syndrome patients within the first 12 h after pain onset, including 20 subjects with type 2 diabetes, 20 subjects with no diagnosed diabetes but with glucose levels >7.0 mmol/l, and 20 subjects with glucose levels <7.0 mmol/l. We determined generation of thrombin-antithrombin complexes (TATs) and soluble CD40 ligand (sCD40L), a platelet activation marker, at the site of microvascular injury, together with ex vivo plasma fibrin clot permeability and lysis time.

RESULTS

The acute coronary syndrome patients with no prior diabetes but elevated glucose levels had increased maximum rates of formation and total production of TATs (by 42.9%, P < 0.0001, and by 25%, P < 0.0001, respectively) as well as sCD40L release (by 16.2%, P = 0.0011, and by 16.3%, P < 0.0001, respectively) compared with those with normoglycemia, whereas diabetic patients had the highest values of TATs and sCD40L variables (P < 0.0001 for all comparisons). Patients with hyperglycemia, with no previously diagnosed diabetes, had longer clot lysis time (by approximately 18%, P < 0.0001) similar to that in diabetic subjects, but not lower clot permeability compared with that in normoglycemic subjects.

CONCLUSIONS

Hyperglycemia in acute coronary syndrome is associated with enhanced local thrombin generation and platelet activation, as well as unfavorably altered clot features in patients with and without a previous history of diabetes.

Tissue factor in thrombosis and hemorrhage

The research aims of our laboratory are to provide a realistic description of biologic processes involved in protection from hemorrhage and the evolution of thrombosis. To evaluate these processes, we use 4 models of coagulation ranging from 1) studies of blood exiting from microvascular wounds in humans through 2) minimally altered whole blood induced to clot by tissue factor (TF) to 3) reconstitution of the blood coagulation proteome with purified components and to 4) mathematical descriptions of the chemical processes and dynamics that occur. The integration of these 4 models permits comprehensive analyses of the blood coagulation system and predictions of its behavior under normal and pathologic conditions. Data accumulated thus far have led to advances in our understanding of 1) the processes occurring during the initiation and propagation phases of thrombin generation, 2) the roles for individual proteins involved in blood coagulation and its regulation, 3) defects in thrombin generation and clot formation in hemophilia, 4) actions and limitations of pharmacologic agents used to control hemorrhage, thrombosis, and chronic cardiovascular disease, and 5) the relationship between genotypic and phenotypic features of an individual's plasma proteome and his/her immediate and long-term thrombotic risk.

A multiparameter test of clot formation and fibrinolysis for in-vitro drug screening

A large spectrum of methods has been used in both routine and scientific studies of the hemostatic system. The particular interest of the investigators has been focused on methods simultaneously evaluating clotting and fibrinolysis processes. The aim of the present study was to develop an optical method for overall evaluation of clot formation and lysis (CL-test) that could be used in drug screening. The CL-test was performed in citrate plasma diluted with Tris-buffered saline. Thrombin was applied for plasma clotting (0.5 IU/ml), while tissue plasminogen activator (60 ng/ml) was used for fibrinolysis activation. Clot formation and lysis were monitored in thermostatic conditions (37 degrees C) as a continuous record of transmittance change. By means of own computer program, kinetic parameters of the processes studied and plasma overall clot formation and fibrinolysis potential, expressed as the area under the clotgeneration and fibrinolysis curves, were calculated. The CL-test was developed and checked by evaluation of the effect, on clot formation and lysis, of various concentrations of acetylsalicylic acid (a drug that affects hemostasis), aprotinin (fibrinolysis activator) and venoruton (fibrinolysis inhibitor). The obtained results confirmed that the test we propose for monitoring clot formation, stabilization and lysis is sensitive and enables precise estimation of the processes studied. In our opinion, it can be a useful tool in drug screening investigations.

Platelets release active matrix metalloproteinase-2in vivoin humans at a site of vascular injury: lack of inhibition by aspirin

When stimulated in vitro, human platelets release matrix metalloproteinase-2 (MMP-2) that, in turn, potentiates platelet activation. The present study investigated if MMP-2 is released from activated platelets in vivo in humans and whether aspirin inhibits this release. MMP-2 levels were measured by zymography, immunoblotting, flow-cytometry and an activity assay system, in plasma prepared from blood emerging from a skin wound inflicted for the measurement of the bleeding time (shed blood) and simultaneously from venous blood in 27 healthy human volunteers. In a subgroup, the same measurements were carried out before and 1 h after aspirin intake. MMP-2 was significantly higher in shed blood than in venous blood and increased progressively, consistent with ongoing platelet activation. A significant correlation was evident between platelet number and MMP-2 in shed blood; platelet MMP-2 content in shed blood was lower than that of platelets in venous blood. The level of active MMP-2 released by activated platelets in vivo was within the range of concentrations that potentiate platelet activation. Aspirin did not reduce MMP-2 release in vivo. In conclusion, MMP-2 is released from platelets in vivo in humans at a localised site of vessel wall damage in amounts sufficient to potentiate platelet aggregation; aspirin does not reduce this release.

Antithrombotic properties of aspirin and resistance to aspirin: beyond strictly antiplatelet actions

Aspirin is effective in the prevention of cardiovascular events in high-risk patients. The primary established effect of aspirin on hemostasis is to impair platelet aggregation via inhibition of platelet thromboxane A(2) synthesis, thus reducing thrombus formation on the surface of the damaged arterial wall. Growing evidence also indicates that aspirin exerts additional antithrombotic effects, which appear to some extent unrelated to platelet thromboxane A(2) production. Aspirin can reduce thrombin generation with the subsequent attenuation of thrombin-mediated coagulant reactions such as factor XIII activation. Aspirin also acetylates lysine residues in fibrinogen resulting in increased fibrin clot permeability and enhanced clot lysis as well as directly promoting fibrinolysis with high-dose aspirin. The variable effectiveness of aspirin in terms of clinical outcomes and laboratory findings, which has been termed aspirin resistance, may be related to these additional antithrombotic effects that are altered when associated with common genetic polymorphisms such as the Leu33Pro beta(3)-integrin or Val34Leu factor XIII mutations. However, the clinical relevance of these observations is still unclear. Elucidation of the actual impacts of aspirin other than antiaggregation effects could be important in view of the widespread use of this drug in the prevention of thrombotic manifestations of atherosclerosis.

Antithrombotic effects of aspirin based on PLA1/A2 glycoprotein IIIa polymorphism in patients with coronary artery disease

OBJECTIVE

The diallelic glycoprotein IIIa polymorphism P1A1/A2 was attributed to be an inherited risk factor for coronary events. Whether this polymorphism affects response to aspirin in patients with coronary artery disease is not known.

METHODS

We assessed thrombin generation (prothrombin fragment F1+2) in consecutive blood samples collected from bleeding-time wounds in 28 men with coronary artery disease; P1A2 carriers, n=9; P1A1/A1, n=19. Thrombin generation and bleeding time were measured before and after 2 weeks of aspirin 300 mg/day.

RESULTS

Aspirin-depressed thrombin generation in A1 homozygotes (p=0.04), but not in A2 carriers. Bleeding time after aspirin was also prolonged in A1 subjects only (p=0.02).

CONCLUSION

Genotyping for glycoprotein IIIa polymorphism might be helpful in predicting antithrombotic action of aspirin in secondary prevention of coronary artery disease.

Atorvastatin and quinapril inhibit blood coagulation in patients with coronary artery disease following 28 days of therapy

BACKGROUND

We evaluated the antithrombotic effects of statins and angiotensin-converting enzyme inhibitor (ACEI) drugs in patients with coronary artery disease (CAD).

METHODS AND RESULTS

Blood coagulation at the site of microvascular injury was assessed in 26 males with CAD before and after treatment with quinapril (10 mg day-1; n=13) or atorvastatin (40 mg day-1; n=13) for 4 weeks and an additional 4 weeks of combined therapy (quinapril+atorvastatin). Rates of prothrombin and factor V activation (FVa), fibrinogen (Fbg) cleavage and FVa inactivation showed that both quinapril and atorvastatin decreased the rates of: formation of thrombin B-chain (by 30.6%, P=0.007; and by 34.3%, P=0.003), formation of thrombin-antithrombin complexes (by 30.4%, P=0.0002; and by 40%, P=0.001), FV activation (by 19.1%, P=0.03; and by 21.8%, P=0.005) and Fbg depletion (by 29.2%, P=0.004; and by 32.7%, P=0.001). Atorvastatin alone accelerated FVa inactivation (P=0.005). A further 4 weeks of combined therapy enhanced most anticoagulant effects only when atorvastatin was added to quinapril.

CONCLUSIONS

In CAD patients, atorvastatin and quinapril slowed blood clotting at the site of microvascular injury after 28 days of therapy. Addition of atorvastatin to quinapril, but not quinapril to the statin, enhanced the anticoagulant effects. Our findings might help explain the reduced risk of myocardial infarction or stroke in patients treated with statins and/or ACEIs and the lack of clinical benefits from ACEI added to prior statin therapy in patients at cardiovascular risk.

The effect of red blood cells on thrombin generation

We have developed an assay of thrombin generation in clotting whole blood. Because our goal was to study patients with red blood cell diseases that are associated with thrombosis, the initial evaluation of this assay analysed the effect of the haematocrit and haemolysate on the total amount of thrombin activity generated and the maximal concentration of thrombin achieved. Both of these parameters were proportional to the haematocrit throughout a wide range of clinically relevant cell concentrations. Red cell lysate also augmented thrombin generation. Because this effect was removed by filtration of the lysate, we propose that it was related to red cell microparticles.

Anticoagulation therapy in microsurgery: a review

The advent of microsurgical tissue transfer including replantation greatly has expanded the scope of reconstructive surgery. There are few recent innovations in anticoagulation therapies for microsurgery, however, and anastomotic thrombosis remains an occasional cause of surgical failure. No consensus exists on the ideal anticoagulation protocol for microsurgery. This article reviews major pharmacologic modalities of anticoagulation, delineates the mechanism of action and study of efficacy of each agent, and compares the risks and benefits of popular anticoagulation therapies. Finally, it examines available human outcomes-based data and attempts to provide a glimpse of the future direction of microsurgical anticoagulation research.

Statins, fenofibrate, and quinapril increase clot permeability and enhance fibrinolysis in patients with coronary artery disease

BACKGROUND

Aspirin increases fibrin clot porosity and susceptibility to lysis. It is unknown whether other drugs, in combination with aspirin, used in the treatment of coronary artery disease (CAD) might affect clot structure and resistance to lysis.

AIM

The aim of the study was to assess the effects of statins, fibrates, or angiotensin-converting enzyme inhibitors (ACEIs) on fibrin clot properties.

PATIENTS AND METHODS

In a randomized double-blind study, men with advanced CAD taking low-dose aspirin were assigned to receive one of the four drugs: simvastatin 40 mg day(-1) (n = 13), atorvastatin 40 mg day(-1) (n = 12), fenofibrate 160 mg day(-1) (n = 12), and quinapril 10 mg day(-1) (n = 11) for 28 +/- 2 days. Moreover, CAD patients (n = 13) taking aspirin (75 mg day(-1)) for 8 weeks were studied after additional 4 weeks on an open-label basis. Thirty men served as healthy controls. Plasma clot permeability and tissue plasminogen activator-induced fibrinolysis were evaluated at baseline and after drug administration.

RESULTS

Permeability increased following the administration of simvastatin (by 20%; P = 0.01), atorvastatin (by 22%; P = 0.001), fenofibrate (by 16%; P = 0.02), and quinapril (by 13%; P = 0.04) like for aspirin (P < 0.001). Turbidity analysis showed that administration of any of the drugs was associated with higher maximum absorbancy, suggesting thicker fibers, and shorter fibrinolysis time (P < 0.001). Post-treatment reduction in lysis time correlated with an increase in clot porosity in all the groups (r from 0.42 to 0.61; P from 0.01 to 0.001).

CONCLUSIONS

Statins, fibrates, and ACEIs may increase plasma clot permeability and susceptibility to fibrinolysis in CAD patients receiving aspirin. This novel antithrombotic mechanism might contribute to clinical benefits of the drugs tested.

Models of blood coagulation

Our research aims to provide quantitatively transparent, biologically realistic descriptions of the processes involved in hemostasis which will permit predictions of the behavior of the coagulation system in normal and pathologic states. We use four models of coagulation: (1) numerical approximations of the tissue factor (Tf) pathway of thrombin generation based upon mechanism and dynamics; (2) Tf activation of the "blood coagulation proteome" from isolated cells and proteins; (3) Tf activated contact pathway inhibited whole blood in vitro; and (4) blood shed from standardized microvascular wounds in vivo. The results from these models are integrated in interactive assessments aimed at achieving convergence of biochemical rigor and biological authenticity. Microvascular injury is the most biologically secure but least accessible to mechanistic study. Numerical models while quantitatively transparent are biologically limited. By the integrated analyses of all four models, we establish observations which require inclusion or discovery of new parameters to achieve mechanistically interpretable biological reality. Discoveries made in this fashion have included thrombin's role in the initiation phase, TFPI/ATIII/APC synergy interactions, rfVIIa in fVII deficiency, the roles of fVIII and fIX in the Tf reaction, and the cleavage of fIX by fXa membrane. Ideally, our results will provide descriptions which predict the behavior of the biological blood coagulation system under normal and pathologic conditions.