Rashid S. Kazmi

Targeting of Antithrombin in Hemophilia A or B with RNAi Therapy

Background Current hemophilia treatment involves frequent intravenous infusions of clotting factors, which is associated with variable hemostatic protection, a high treatment burden, and a risk of the development of inhibitory alloantibodies. Fitusiran, an investigational RNA interference (RNAi) therapy that targets antithrombin (encoded by SERPINC1), is in development to address these and other limitations. Methods In this phase 1 dose‐escalation study, we enrolled 4 healthy volunteers and 25 participants with moderate or severe hemophilia A or B who did not have inhibitory alloantibodies. Healthy volunteers received a single subcutaneous injection of fitusiran (at a dose of 0.03 mg per kilogram of body weight) or placebo. The participants with hemophilia received three injections of fitusiran administered either once weekly (at a dose of 0.015, 0.045, or 0.075 mg per kilogram) or once monthly (at a dose of 0.225, 0.45, 0.9, or 1.8 mg per kilogram or a fixed dose of 80 mg). The study objectives were to assess the pharmacokinetic and pharmacodynamic characteristics and safety of fitusiran. Results No thromboembolic events were observed during the study. The most common adverse events were mild injection‐site reactions. Plasma levels of fitusiran increased in a dose‐dependent manner and showed no accumulation with repeated administration. The monthly regimen induced a dose‐dependent mean maximum antithrombin reduction of 70 to 89% from baseline. A reduction in the antithrombin level of more than 75% from baseline resulted in median peak thrombin values at the lower end of the range observed in healthy participants. Conclusions Once‐monthly subcutaneous administration of fitusiran resulted in dose‐dependent lowering of the antithrombin level and increased thrombin generation in participants with hemophilia A or B who did not have inhibitory alloantibodies. (Funded by Alnylam Pharmaceuticals; ClinicalTrials.gov number, NCT02035605.)

New anticoagulants: how to deal with treatment failure and bleeding complications

Conventional anticoagulants have proven efficacy in the management of thromboembolism. Their adverse effects and a narrow therapeutic window, necessitating regular need for monitoring, however, have long been an incentive for the development of safer anticoagulants without compromising efficacy. Over the last decade or so several new parenteral and oral anticoagulants have been launched with efficacy comparable with conventional agents. From fondaparinux to its long acting derivative idraparinux, and the factor Xa inhibitor rivaroxaban to the direct thrombin inhibitor dabigatran, the advent of new anticoagulants is radically changing anticoagulation. For conventional anticoagulants, despite their shortcomings, effective methods of reversing their anticoagulant effects exist. Moreover, strategies to deal with the occurrence of fresh thrombotic events in the face of therapeutic anticoagulation with the conventional agents have also been addressed. Nevertheless, for the new anticoagulants, the optimal management of these complications remains unknown. This review explores these issues in the light of current evidence.

Platelet function in pre-eclampsia

Pronounced hemostatic changes occur during pregnancy, and the balance shifts markedly in favor of hypercoagulability. Although primarily a result of a marked rise in the levels of several procoagulants and a fall in some natural anticoagulants, platelet activation also contributes to this prothrombotic tendency. Several studies have confirmed the accentuation of platelet activation in pre-eclampsia (P-EC), which remains an important obstetric complication affecting ~2 to 4% of pregnancies. Although there is still a long way to go, significant inroads have been made in the understanding of this enigmatic condition. Whereas the pathogenesis of P-EC is protean and involves a complex interplay of placental and maternal tissues, platelet activation is likely to contribute to several clinical features. Several techniques have been used to assess platelet activation in P-EC. Detection of aberrations of platelet function and activation appear to have predictive value for its diagnosis. The findings also lend support to the use of antiplatelet agents as prophylaxis in those women with a high risk of developing the condition.

Homeostasis of hemostasis: the role of endothelium

Forming an interface with virtually every other organ, endothelium has a strategic role in modulating vascular homeostasis. While its miscellany of functions includes regulation of vasomotor tone, promotion, and prevention of vascular growth, and modulation of inflammatory and hemostatic processes, it functions critically in maintaining the balance of hemostasis in health. Whereas endothelium has been recognized to influence all stages of hemostasis, new evidence suggests it to have a primary role for thrombin generation. Endothelial dysfunction is being increasingly appreciated in several pathological states and particularly, by virtue of its critical role in hemostasis, in causing thrombosis in a multitude of diseases.

Elevated plasma factor VIII and von Willebrand factor in women with type 2 diabetes: inflammatory reaction, endothelial perturbation or else?

The association between type 2 diabetes and cardiovascular disease is long recognized. Although perturbations of haemostatic markers have been shown to be associated with macrovascular disease in patients with type 2 diabetes, it is unclear whether these are primarily due to endothelial dysfunction or a result of inflammation. The present study was undertaken to elucidate whether elevated levels of factor VIII (FVIII) and von Willebrand factor (vWF) in women with type 2 diabetes represent endothelial dysfunction, inflammation or an alternate mechanism. Sixty-four women with type 2 diabetes were evaluated using ultrasonography Doppler for carotid intima–media thickness (IMT) and were classified as group A – having no (<1 mm), group B – mild (≥1 mm and no plaque) and group C – moderate (≥1 mm and presence of plaque and stenosis) macrovascular disease. Several haemostatic markers including, FVIII, vWF and fibrinogen were assessed. In addition, thrombomodulin, a marker for endothelial damage, and high-sensitivity C-reactive protein (hsCRP), an inflammatory marker, were also measured. A significant association of elevated FVIII was found in group B and C patients (i.e. patients with IMT ≥1 mm and with plaque). Elevated fibrinogen and vWF levels were also found but confined to group C patients. No significant difference among subgroups was found for any other variable evaluated (hsCRP, thrombomodulin and FVII). In conclusion, plasma FVIII levels are elevated in women with type 2 diabetes and macrovascular disease. It also appears that this is not mediated by inflammation or endothelial injury and is likely to be due to an alternate mechanism.

Gastrointestinal bleeding and aortic stenosis (Heyde Syndrome): the role of aortic valve replacement

Heyde syndrome (the combination of iron deficiency anemia and aortic stenosis) has been a controversial entity. The proposed mechanisms between aortic valve disease and iron deficiency anemia are examined in this article along with impact valve replacement on iron deficiency anemia. doi: 10.1111/jocs.12131 (J Card Surg 2013;28:414–416)

The Activation of Complement and Its Role in the Pathogenesis of Thromboembolism.

It is well established that inflammation and thrombosis are intricately linked processes, and there is increasing evidence of the importance of their roles in activated complement in the pathogenesis of thromboembolism. The two systems are activated by similar stimuli simultaneously and interact, either directly or through biochemical mediators, to protect the host from microbial invasion. Diseases characterized by complement hyperactivity such as paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome have high rates of thrombosis. This review describes how disease processes where there is excessive complement activation leads to thrombosis, and the specific interactions between the complement and coagulation systems that lead to pathological thrombus formation.

Sources of Thrombomodulin in Pre-Eclampsia: Renal Dysfunction or Endothelial Damage?

A plethora of evidence exists to show that endothelial perturbations underlie many of the clinical features of pre-eclampsia (P-EC), and consequently the markers signifying endothelial disturbance exhibit a rise in plasma. Among others, plasma thrombomodulin (TM) level rises significantly. TM is a transmembrane glycoprotein expressed abundantly on the endothelium of the microvasculature. It neutralizes the thrombotic potential of thrombin, mediating this anticoagulant effect through activation of protein C. Endothelial injury results in a localized loss of TM with a focal impairment of protein C activation and resultant thrombotic tendency. Mainly expressed on the endothelial cells, a small amount of TM is found in plasma with levels rising in certain pathological conditions. Although elevation in levels of TM can be due to endothelial TM proteolysis secondary to endothelial insult, ineffective clearance may account for this in renal and hepatic dysfunction. In P-EC not only is there ongoing endothelial injury, but renal function is also affected. To establish the cause of elevated TM level in P-EC, three groups of pregnant women were investigated. It appears that the elevation in plasma TM is not related to renal or hepatic dysfunction in P-EC. It is more likely that plasma TM is derived from placental or vascular endothelial cells subsequent to activation or damage, confirming the hypothesis that damage to vascular endothelial cells is the primary underlying cause of P-EC.

Plasminogen and fibrinogen plasma levels in coronary artery disease.

OBJECTIVE: The formation of thrombi at the site of atherosclerotic lesions plays a central role in atherothrombosis. Impaired fibrinolysis may exacerbate pre-existing coronary artery disease and potentiate its evolution. While the fibrinogen plasma level has been strongly associated with the severity of coronary artery disease, its relevance in the evaluation of plasminogen in coronary artery disease patients remains unclear. This study evaluated fibrinogen and plasminogen levels in subjects with coronary artery disease as diagnosed by angiography. METHODS: This is a cross-sectional study. Blood samples obtained from 17 subjects with angiographically normal coronary arteries (controls), 12 with mild/moderate atheromatosis and 28 with severe atheromatosis were evaluated. Plasma plasminogen and fibrinogen levels were measured by chromogenic and coagulometric methods, respectively. RESULTS: Fibrinogen levels were significantly higher in the severe atheromatosis group compared to the other groups(p-value < 0.0001). A significant positive correlation was observed between the severity of coronary artery diseaseand increasing fibrinogen levels (r = 0.50; p-value < 0.0001) and between fibrinogen and plasminogen levels (r =0.46; p-value < 0.0001). There were no significant differences in the plasminogen levels between groups. CONCLUSION: Plasma fibrinogen, but not plasminogen levels were higher in patients with coronary artery disease compared to angiographically normal subjects. The plasma fibrinogen levels also appear to be associated with the severity of the disease. The results of this study provide no evidence of a significant correlation between plasma plasminogen levels and the progress of coronary stenosis in the study population.

Inflammation, Endothelial Dysfunction, and Thromboembolism.

Inflammatory mechanisms are intimately tied up with direct defense against infection, immunity, and healing. In order for processes to proceed at affected sites within tissues, capillary walls have to be able to modify their permeability to soluble mediators, particles, and cells. These systems are in a delicate balance, which can be easily disrupted, giving rise to exacerbating diseases or dysfunctions. The situation is further complicated by the equally sensitive homoeostatic mechanisms controlling thrombosis and fibrinolysis, which are also involved in defense against environmental damage and tissue repair and they are most active in the circulation and at the blood/tissue interface. This issue of Seminars in Thrombosis & Hemostasis embraces awide range of pathologies that exhibit dysfunctionality in this web of fluid interactions. All tissues of any size (perhaps the most well-documented example is the >2 mm minimum normally quoted in cancer biology), normal or abnormal, need nutritional and hormonal support from blood, throughmicrovasculature. Inflammation requires cellular traffic between endothelial cells and through capillary walls. Maintaining fluidity in plasma without compromising its ability to coagulate at times and places of need is a fundamental homoeostatic mechanism in all warmblooded and at least in some poikilothermic animals. It is unsurprising that aberrations in this system are commonly causes or sequelae of diseases. This general proposition is expanded in the article by Dr. Kazmi and associates.1 A time-honored view might be that coagulation is a localized extracellular process mediated by soluble factors activated by an altered surface. Seeking amore specific theme in this issue, it might be characterized as the activities of extracellular structures, typically completely independent microparticles, neutrophil extracellular traps (NETs) as described by Drs. Matevosyan and Sarode,2 which are composed of fibrillar DNA and protein in strands up to 50 nm wide (like the eukaryotic equivalent of a bacterial biofilm), or the chunky extracellular domains of integrins, anchored to their parent cell membranes. The latter are discussed by Drs. Allen and Moran3 as attractive therapeutic targets in a range of diseases, their theoretical utility hampered by redundancy on one hand and their wide importance in key physiological systems on the other hand. Arguably, platelets represent the earliest described “microparticle,” albeit at 2 to 3 μM toward the upper end of a scale generally considered to go down to 0.1 μM. Platelets are the main focus of the contributions from Dr. Thachil,4 where research findings are related to present and future therapies, the latter extending frommanipulation of numbers to influencing their interactions with leukocytes or endothelial cells as in the article by Dr. Senchenkova and coworkers,5 where an inflammatory cytokine-induced increase in production of platelets is implicated in the pathogenesis of inflammatory bowel disease. Aggregation and interaction between platelets are also observed in that condition. Microparticles, as conventionally defined are vesicles in the 0.1 to 1μM diameter range, budded off from cells are discussed in the context of atherosclerosis and inflammation in cardiovascular disease by Dr. Suades and colleagues.6Novel functions ascribed to microparticles, besides their utility as biomarkers, include mechanisms to alter the vascular cell milieu, disseminating proinflammatory mediators ultimately causing vascular wall inflammation, aggravating the atherothrombosis. It is the role of plasma protein β2-glycoprotein I in the clearance of microparticles that prompts Drs. de Groot and Urbanus7 to argue in favor of an inflammatory