Direct Oral FXa Inhibitors Binding to Human Serum Albumin: Spectroscopic, Calorimetric, and Computational Studies.

Direct FXa inhibitors are an important class of bioactive molecules (rivaroxaban, apixaban, edoxaban, and betrixaban) applied for thromboprophylaxis in diverse cardiovascular pathologies. The interaction of active compounds with human serum albumin (HSA), the most abundant protein in blood plasma, is a key research area and provides crucial information about drugs' pharmacokinetics and pharmacodynamic properties. This research focuses on the study of the interactions between HSA and four commercially available direct oral FXa inhibitors, applying methodologies including steady-state and time-resolved fluorescence, isothermal titration calorimetry (ITC), and molecular dynamics. The HSA complexation of FXa inhibitors was found to occur via static quenching, and the complex formation in the ground states affects the fluorescence of HSA, with a moderate binding constant of 104 M-1. However, the ITC studies reported significantly different binding constants (103 M-1) compared with the results obtained through spectrophotometric methods. The suspected binding mode is supported by molecular dynamics simulations, where the predominant interactions were hydrogen bonds and hydrophobic interactions (mainly π-π stacking interactions between the phenyl ring of FXa inhibitors and the indole moiety of Trp214). Finally, the possible implications of the obtained results regarding pathologies such as hypoalbuminemia are briefly discussed.

Clotting factor genes are associated with preeclampsia in high-altitude pregnant women in the Peruvian Andes.

Preeclampsia is a multi-organ complication of pregnancy characterized by sudden hypertension and proteinuria that is among the leading causes of preterm delivery and maternal morbidity and mortality worldwide. The heterogeneity of preeclampsia poses a challenge for understanding its etiology and molecular basis. Intriguingly, risk for the condition increases in high-altitude regions such as the Peruvian Andes. To investigate the genetic basis of preeclampsia in a population living at high altitude, we characterized genome-wide variation in a cohort of preeclamptic and healthy Andean families (n = 883) from Puno, Peru, a city located above 3,800 meters of altitude. Our study collected genomic DNA and medical records from case-control trios and duos in local hospital settings. We generated genotype data for 439,314 SNPs, determined global ancestry patterns, and mapped associations between genetic variants and preeclampsia phenotypes. A transmission disequilibrium test (TDT) revealed variants near genes of biological importance for placental and blood vessel function. The top candidate region was found on chromosome 13 of the fetal genome and contains clotting factor genes PROZ, F7, and F10. These findings provide supporting evidence that common genetic variants within coagulation genes play an important role in preeclampsia. A selection scan revealed a potential adaptive signal around the ADAM12 locus on chromosome 10, implicated in pregnancy disorders. Our discovery of an association in a functional pathway relevant to pregnancy physiology in an understudied population of Native American origin demonstrates the increased power of family-based study design and underscores the importance of conducting genetic research in diverse populations.

Coagulotoxicity of Bothrops (Lancehead Pit-Vipers) Venoms from Brazil: Differential Biochemistry and Antivenom Efficacy Resulting from Prey-Driven Venom Variation.

Lancehead pit-vipers (Bothrops genus) are an extremely diverse and medically important group responsible for the greatest number of snakebite envenomations and deaths in South America. Bothrops atrox (common lancehead), responsible for majority of snakebites and related deaths within the Brazilian Amazon, is a highly adaptable and widely distributed species, whose venom variability has been related to several factors, including geographical distribution and habitat type. This study examined venoms from four B. atrox populations (Belterra and Santarém, PA; Pres. Figueiredo, AM and São Bento, MA), and two additional Bothrops species (B. jararaca and B. neuwiedi) from Southeastern region for their coagulotoxic effects upon different plasmas (human, amphibian, and avian). The results revealed inter⁻ and intraspecific variations in coagulotoxicity, including distinct activities between the three plasmas, with variations in the latter two linked to ecological niche occupied by the snakes. Also examined were the correlated biochemical mechanisms of venom action. Significant variation in the relative reliance upon the cofactors calcium and phospholipid were revealed, and the relative dependency did not significantly correlate with potency. Relative levels of Factor X or prothrombin activating toxins correlated with prey type and prey escape potential. The antivenom was shown to perform better in neutralising prothrombin activation activity than neutralising Factor X activation activity. Thus, the data reveal new information regarding the evolutionary selection pressures shaping snake venom evolution, while also having significant implications for the treatment of the envenomed patient. These results are, therefore, an intersection between evolutionary biology and clinical medicine.

Human Cells as Platform to Produce Gamma-Carboxylated Proteins.

The gamma-carboxylated proteins belong to a family of proteins that depend on vitamin K for normal biosynthesis. The major representative gamma-carboxylated proteins are the coagulation system proteins, for example, factor VII, factor IX, factor X, prothrombin, and proteins C, S, and Z. These molecules have harbored posttranslational modifications, such as glycosylation and gamma-carboxylation, and for this reason they need to be produced in mammalian cell lines. Human cells lines have emerged as the most promising alternative to the production of gamma-carboxylated proteins. In this chapter, the methods to generate human cells as a platform to produce gamma-carboxylated proteins, for example the coagulation factors VII and IX, are presented. From the cell line modification up to the vitamin K adaptation of the produced cells is described in the protocols presented in this chapter.

Terapias anticoagulantes na doença renal crônica / Anticoagulant therapies in chronic renal disease

Os pacientes com doença renal crônica (DRC) têm tendências hemorrágicas e trombóticas e, por isso, a indicação de anticoagulantes é complexa nos indivíduos com fibrilação atrial (FA). A FA é a arritmia mais frequente na DRC, sendo o tromboembolismo e o ictus suas principais complicações. A introdução de novos anticoagulantes orais diretos (DOACs) tem se mostrado superior aos antagonistas da vitamina K, tanto na prevenção de tromboembolismos sistêmicos como no risco de sangramento. Contudo, devem ser prescritos com cautela nesse grupo de pacientes. Para os indivíduos com DRC e clearance renal entre 30 e 50 ml/min, as doses da dabigatrana e da rivaroxabana devem ser reduzidas, no caso de pacientes com elevado risco de sangramento, não havendo necessidade de reduzir as doses de apixabana e edoxabana. Em pacientes com clearance renal entre 15 e 29 ml/min o uso da dabigatrana é contraindicado, a rivaroxabana e a edoxabana não exigem ajuste terapêutico e a dose de apixabana deve ser ajustada. Nenhum dos DOACs é indicado em pacientes com clearance renal < 15 mg/min. Outro problema da terapêutica com os DOACs é o custo do medicamento, muito superior aos dos antagonistas da vitamina K, trazendo algumas implicações clínicas relevantes: suspensão terapêutica por restrições econômicas, que mesmo quando transitória, coloca o paciente em risco de eventos tromboembólicos devido à perda rápida de seus efeitos anticoagulantes e pela possibilidade de hipercoagulabilidade paradoxal. A maior parte da população é tratada em hospitais públicos e recebe os antagonistas de vitamina K. Por isso, enquanto a relação custo-efetividade dos DOACs não for esclarecida, a prevenção e o tratamento de pacientes com DRC e FA com os antagonistas de vitamina K estão consagrados e podem trazer benefícios para esse grupo de pacientes

Patients with chronic renal disease (CRD) have hemorrhagic and thrombotic tendencies, therefore the indication of anticoagulants is complex in individuals with atrial fibrillation (AF). AF is the most frequent arrhythmia in CRD, and thromboembolism and cerebral stroke are its main complications. The introduction of new oral anticoagulants (DOACs) has proven to be superior to vitamin K antagonists in preventing systemic thromboembolisms and bleeding risk. However, they should be prescribed with caution in this group of patients. For individuals with CRD and renal clearance between 30 and 50 ml/min, the doses of dabigatran and rivaroxaban should be reduced, in the case of patients with high risk of bleeding, and it is not necessary to reduce the doses of apixaban and edoxaban. In patients with renal clearance between 15 and 29 ml/min, the use of dabigatran is contraindicated, rivaroxaban and edoxaban do not require therapeutic adjustment, and the dose of apixaban should be adjusted. No DOACs is indicated in patients with renal clearance < 15 mg/min. Another problem with DOACs therapy is the cost of the medication, which is much higher than that of vitamin K antagonists, with some important clinical implications: therapeutic suspension due to economic restrictions, even if temporary, place the patient at risk of thromboembolic events due to the rapid loss of anticoagulant effects and the possibility of paradoxical hypercoagulability. Most of the population is treated in public hospitals, and receives vitamin K antagonists. Therefore, while the cost-effectiveness ratio of DOACs has not been clarified, prevention and treatment of patients with CRD and AF with vitamin K antagonists is consecrated, and can bring benefits for this group of patients

A family with factor X deficiency from Argentina: a compound heterozygosis because of the combination of a new mutation (Gln138Arg) with an already known one (Glu350Lys).

The objective was to investigate a family from Argentina. The proposita was a 51-year-old woman who had a moderate bleeding tendency. Some of her children showed a mild bleeding tendency. Her mother and the husband were asymptomatic. Clotting, immunological and molecular biology techniques were used. Partial thromboplastin, prothrombin, Russell Viper venom-clotting times were moderately prolonged in the proposita, whereas they were slightly prolonged in the children and in her mother. Factor X (FX) activity was about 2-3% of normal in all assay systems. FX antigen was less than 5%. Other clotting factors and platelet were normal. Genetic analysis showed a compound heterozygosis: combination of a 'new' mutation (Gln138Arg) with an already known mutation (Glu350Lys). The children had intermediate FX levels (35-63% of normal) and were carriers of one of the two mutations present in the proposita. This is the first observation of a FX deficiency in Argentina.

Ex vivo evaluation of 4 different viscoelastic assays for detecting moderate to severe coagulopathy during liver transplantation.

Prolonged prothrombin time (PT) and its ratio are routinely used for the assessment of candidates for liver transplantation (LT), but intraoperative coagulation management of transfusion is hindered by its long turnaround time. Abnormal reaction time (R time) on thromboelastography (TEG) or clotting time (CT) of rotational thromboelastometry (ROTEM) are presumably an alternative, but there is a paucity of clinical data on abnormal R time/CT values compared to PT during LT. After receiving institutional review board approval and informed consent, we obtained blood samples from 36 LT patients for international normalized ratio (INR), factor (F) X level, and viscoelastic tests (EXTEM/INTEM and kaolin/rapid TEG) at baseline and 30 minutes after graft reperfusion. Receiver operating characteristic (ROC) curves were calculated for INR > 1.5 and viscoelastic R time/CT thresholds to assess the ability to diagnose FX deficiency at the moderate (<50%) or severe (<35%) level. The FX deficiency data were calculated using cutoff values of INR (>1.5) and abnormal R time/CT for TEG and ROTEM. Tissue factor (TF)-activated INR and EXTEM-CT performed well in diagnosing FX below 50%, but rapid TEG with combined TF and kaolin activators failed. Improved performance of INTEM-CT in diagnosing FX below 35% underlies multifactorial deficiency involving both intrinsic and common pathways. In conclusion, the differences among different viscoelastic tests and clinical situations should be carefully considered when they are used to guide transfusion during LT.

Bothrops jararaca envenomation: Pathogenesis of hemostatic disturbances and intravascular hemolysis.

To attain fully functional biological activity, vitamin-K dependent coagulation factors (VKDCF) are γ-carboxylated prior to secretion from liver. Warfarin impairs the γ-carboxylation, and consequently their physiological function. Bothrops jararaca snake venom (BjV) contains several activators of blood coagulation, especially procoagulant enzymes (prothrombin and factor X activators) and thrombin-like enzymes. In order to clarify the relative contribution of prothrombin and factor X activators to the hemostatic disturbances occurring during experimental B. jararaca envenomation, warfarin was used to deplete VKDCF, prior to BjV administration. Male Wistar rats were pretreated with saline (Sal) or warfarin (War) and inoculated subsequently with BjV or saline, thus forming four groups: Sal + Sal (negative control), Sal + BjV (positive control), War + Sal (warfarinization control), and War + BjV. Three hours after inoculation, prothrombin and factor X levels fell 40% and 50%, respectively; levels of both factors decreased more than 97% in the War + Sal and War + BjV groups. Platelet counts dropped 93% and 76% in Sal + BjV and War + BjV, respectively, and plasma fibrinogen levels decreased 86% exclusively in Sal + BjV. After 6 and 24 h, platelet counts and fibrinogen levels increased progressively. A dramatic augmentation in plasma hemoglobin levels and the presence of schizocytes and microcytes in the Sal + BjV group indicated the development of intravascular hemolysis, which was prevented by warfarin pretreatment. Our findings show that intravascular thrombin generation has the foremost role in the pathogenesis of coagulopathy and intravascular hemolysis, but not in the development of thrombocytopenia, in B. jararaca envenomation in rats; in addition, fibrinogenases (metalloproteinases) may contribute to coagulopathy more than thrombin-like enzymes.

Functional variability of snake venom metalloproteinases: adaptive advantages in targeting different prey and implications for human envenomation.

Snake venom metalloproteinases (SVMPs) are major components in most viperid venoms that induce disturbances in the hemostatic system and tissues of animals envenomated by snakes. These disturbances are involved in human pathology of snake bites and appear to be essential for the capture and digestion of snake's prey and avoidance of predators. SVMPs are a versatile family of venom toxins acting on different hemostatic targets which are present in venoms in distinct structural forms. However, the reason why a large number of different SVMPs are expressed in some venoms is still unclear. In this study, we evaluated the interference of five isolated SVMPs in blood coagulation of humans, birds and small rodents. P-III class SVMPs (fractions Ic, IIb and IIc) possess gelatinolytic and hemorrhagic activities, and, of these, two also show fibrinolytic activity. P-I class SVMPs (fractions IVa and IVb) are only fibrinolytic. P-III class SVMPs reduced clotting time of human plasma. Fraction IIc was characterized as prothrombin activator and fraction Ic as factor X activator. In the absence of Ca2+, a firm clot was observed in chicken blood samples with fractions Ic, IIb and partially with fraction IIc. In contrast, without Ca2+, only fraction IIc was able to induce a firm clot in rat blood. In conclusion, functionally distinct forms of SVMPs were found in B. neuwiedi venom that affect distinct mechanisms in the coagulation system of humans, birds and small rodents. Distinct SVMPs appear to be more specialized to rat or chicken blood, strengthening the current hypothesis that toxin diversity enhances the possibilities of the snakes for hunting different prey or evading different predators. This functional diversity also impacts the complexity of human envenoming since different hemostatic mechanisms will be targeted by SVMPs accounting for the complexity of the response of humans to venoms.

Independent anti-angiogenic capacities of coagulation factors X and Xa.

Knockout models have shown that the coagulation system has a role in vascular development and angiogenesis. Herein, we report for the first time that zymogen FX and its active form (FXa) possess anti-angiogenic properties. Both the recombinant FX and FXa inhibit angiogenesis in vitro using endothelial EA.hy926 and human umbilical cord vascular endothelial cells (HUVEC). This effect is dependent on the Gla domain of FX. We demonstrate that FX and FXa use different mechanisms: the use of Rivaroxaban (RX) a specific inhibitor of FXa attenuated its anti-angiogenic properties but did not modify the anti-angiogenic effect of FX. Furthermore, only the anti-angiogenic activity of FXa is PAR-1dependent. Using in vivo models, we show that FX and FXa are anti-angiogenic in the zebrafish intersegmental vasculature (ISV) formation and in the chick embryo chorioallantoic membrane (CAM) assays. Our results provide further evidence for the non-hemostatic functions of FX and FXa and demonstrate for the first time a biological role for the zymogen FX.

Leishmania amazonensis exhibits phosphatidylserine-dependent procoagulant activity, a process that is counteracted by sandfly saliva.

Leishmania parasites expose phosphatidylserine (PS) on their surface, a process that has been associated with regulation of host's immune responses. In this study we demonstrate that PS exposure by metacyclic promastigotes of Leishmania amazonensis favours blood coagulation. L. amazonensis accelerates in vitro coagulation of human plasma. In addition, L. amazonensis supports the assembly of the prothrombinase complex, thus promoting thrombin formation. This process was reversed by annexin V which blocks PS binding sites. During blood meal, Lutzomyia longipalpis sandfly inject saliva in the bite site, which has a series of pharmacologically active compounds that inhibit blood coagulation. Since saliva and parasites are co-injected in the host during natural transmission, we evaluated the anticoagulant properties of sandfly saliva in counteracting the procoagulant activity of L. amazonensis . Lu. longipalpis saliva reverses plasma clotting promoted by promastigotes. It also inhibits thrombin formation by the prothrombinase complex assembled either in phosphatidylcholine (PC)/PS vesicles or in L. amazonensis . Sandfly saliva inhibits factor X activation by the intrinsic tenase complex assembled on PC/PS vesicles and blocks factor Xa catalytic activity. Altogether our results show that metacyclic promastigotes of L. amazonensis are procoagulant due to PS exposure. Notably, this effect is efficiently counteracted by sandfly saliva.

Leishmania amazonensis exhibits phosphatidylserine-dependent procoagulant activity, a process that is counteracted by sandfly saliva

Leishmania parasites expose phosphatidylserine (PS) on their surface, a process that has been associated with regulation of host's immune responses. In this study we demonstrate that PS exposure by metacyclic promastigotes of Leishmania amazonensis favours blood coagulation. L. amazonensis accelerates in vitro coagulation of human plasma. In addition, L. amazonensis supports the assembly of the prothrombinase complex, thus promoting thrombin formation. This process was reversed by annexin V which blocks PS binding sites. During blood meal, Lutzomyia longipalpis sandfly inject saliva in the bite site, which has a series of pharmacologically active compounds that inhibit blood coagulation. Since saliva and parasites are co-injected in the host during natural transmission, we evaluated the anticoagulant properties of sandfly saliva in counteracting the procoagulant activity of L. amazonensis . Lu. longipalpis saliva reverses plasma clotting promoted by promastigotes. It also inhibits thrombin formation by the prothrombinase complex assembled either in phosphatidylcholine (PC)/PS vesicles or in L. amazonensis . Sandfly saliva inhibits factor X activation by the intrinsic tenase complex assembled on PC/PS vesicles and blocks factor Xa catalytic activity. Altogether our results show that metacyclic promastigotes of L. amazonensis are procoagulant due to PS exposure. Notably, this effect is efficiently counteracted by sandfly saliva.

La importancia de la determinación del factor X activado para la anticoagulación con heparinas de bajo peso molecular: experiencia en el hospital san juan de dios, 2009-2011 (primer reporte) / The importance of the determination of factor X acivated for anticoagulation with low molecularweight heparins experience at the hospital san juan de dios. (first report) 2009-2011

La anticoagulación con heparinas de bajo peso molecular (HBPM) es una herramienta terapéutica fundamental para el tratamiento de la enfermedad tromboembólica. En el presente reporte se evidencia la importancia de cuantificar la actividad del anticuerpo antifactor X activado (Xa) para el monitoreo de la enoxaparina y analizar los grupos de pacientes en riesgo de tener niveles inferiores al terap‚utico. M‚todos: se estudiaron 34 pacientes adultos, anticoagulados con enoxaparina durante el periodo 2009-2011. Asimismo, se realizó un análisis descriptivo de las características demográficas y clínicas de todo los pacientes, en donde se indicaron las causas de la anticoagulación, la comorbilidades y el tipo de anticoagulación. Se midió la actividad anti-Xa 4 horas después de la administración de enoxaparina. Resultados: El promedio de edad de los pacientes fue de 62,3+17,7 años. Un 72,71 por ciento de los pacientes utilizaron enoxaparina como indicación para el síndrome coronario agudo. La comorbilidad más importante fue la combinación con la hipertensión arterial. El aclaramiento renal promedio fue de 62,47 ml/min, solamente tres pacientes tuvieron un aclaramiento menor a 30 ml/min; un 44,1 por ciento de los pacientes eran obesos. El 55,9 por ciento de los pacientes tuvo niveles anti-factor Xa dentro del rango terapéutico y un 35,3 por ciento tuvo valores de anti factor Xa profilácticos. Conclusión: El manejo del paciente adulto que recibe terapia anticoagulación con HBPM presenta una alta complejidad, hecho que se ve reflejado tanto a su perfil demográfico como clínico. También, se considera importante contar con la determinación del factor anti Xa para el monitoreo de HBPM para cierto grupo de pacientes vulnerables y con ello lograr el efecto deseado con esta terapia, debido a que existe un alto porcentaje de pacientes con niveles fuera del rango terapéutico.

Anticoagulation is an important therapeutic tool for patients with thromboembolic disease who receive therapy with lowmolecular weight heparins (LMWH). This report gives evidence about the importance of determining the activity of Anti-Xaactivity for monitoring enoxaparin and for identifying those patients who need this analysis based on some risk factors.Methods: We studied 34 adult patients who received enoxaparin as anticoagulation therapy during the period 2009-2011. We performed a descriptive analysis of demographic and clinical characteristics of all patients, indicating thereasons for anticoagulation, comorbidities and type of anticoagulation. We determined the anti-Xa activity 4 hours afteradministration of enoxaparin.Results: The mean age of patients was 62,3 + 17,7 years, regardless of gender. 72,7% of patients received enoxaparin astherapy for an acute coronary syndrome. The most frequent comorbidity was hypertension. The average of renal clearancewas 62,47 ml/min, only three patients had a renal clearance below 30 ml/min. 44,1% of the patients were obese. 55, 9%of patients were within therapeutic levels of anti-Xa activity and 35,3% of patients had an anti-Xa activity considered asprophylactic.Conclusion: The management of adult patients receiving anticoagulation therapy with LMWH is complex and it isreflected in their demographic and clinical characteristics. It is important to determine Anti-Xa activity to monitor the useof enoxaparin as anticoagulant therapy because of the high variability found in certain groups of patients.

Progesterone utilizes distinct membrane pools of tissue factor to increase coagulation and invasion and these effects are inhibited by TFPI.

Tissue factor (TF) serving as the receptor for coagulation factor VII (FVII) initiates the extrinsic coagulation pathway. We previously demonstrated that progesterone increases TF, coagulation and invasion in breast cancer cell lines. Herein, we investigated if tissue factor pathway inhibitor (TFPI) could down-regulate progesterone-increased TF activity in these cells. Classically, TFPI redistributes TF-FVII-FX-TFPI in an inactive quaternary complex to membrane associated lipid raft regions. Herein, we demonstrate that TF increased by progesterone is localized to the heavy membrane fraction, despite progesterone-increased coagulation originating almost exclusively from lipid raft domains, where TF levels are extremely low. The progesterone increase in coagulation is not a rapid effect, but is progesterone receptor (PR) dependent and requires protein synthesis. Although a partial relocalization of TF occurs, TFPI does not require the redistribution to lipid rafts to inhibit coagulation or invasion. Inhibition by TFPI and anti-TF antibodies in lipid raft membrane fractions confirmed the dependence on TF for progesterone-mediated coagulation. Through the use of pathway inhibitors, we further demonstrate that the TF up-regulated by progesterone is not coupled to the progesterone increase in TF-mediated coagulation. However, the progesterone up-regulated TF protein may be involved in progesterone-mediated breast cancer cell invasion, which TFPI also inhibits.

Losac, the first hemolin that exhibits procogulant activity through selective factor X proteolytic activation.

Envenoming by the contact of human skin with Lonomia obliqua caterpillars promotes a hemorrhagic syndrome characterized by a consumptive coagulopathy. Losac (Lonomia obliqua Stuart factor activator) is a component of the bristle of L. obliqua that is probably partially responsible for the observed syndrome because it activates factor X and is recognized by an effective antilonomic serum. Here we unveil the proteolytic activity of Losac and demonstrate the feasibility of its recombinant production. On the other hand, Losac has no homology to known proteases, but it can be inhibited by PMSF, a serine protease inhibitor. Instead, it shows closer homology to members of the hemolin family of proteins, a group of cell adhesion molecules. The recombinant protein (rLosac) shortened the coagulation time of normal and deficient plasmas, whereas it was ineffective in factor X-deficient plasma unless reconstituted with this protein. rLosac was able to activate factor X in a dose- and time-dependent manner but not γ-carboxyglutamic acid domainless factor X. Moreover, phospholipids and calcium ions increased rLosac activity. Also, rLosac had no effect on fibrin or fibrinogen, indicating its specificity for blood coagulation activation. Linear double reciprocal plots indicate that rLosac follows a Michaelis-Menten kinetics. Cleavage of factor X by rLosac resulted in fragments that are compatible with those generated by RVV-X (a well known factor X activator). Together, our results validate Losac as the first protein from the hemolin family exhibiting procoagulant activity through selective proteolysis on coagulation factor X.

Losac, the first hemolin that exhibits procogulant activity through selective factor X proteolytic activation

Envenoming by the contact of human skin with Lonomia obliqua caterpillars promotes a hemorrhagic syndrome characterized by a consumptive coagulopathy. Losac (Lonomia obliqua Stuart factor activator) is a component of the bristle of L. obliqua that is probably partially responsible for the observed syndrome because it activates factor X and is recognized by an effective antilonomic serum. Here we unveil the proteolytic activity of Losac and demonstrate the feasibility of its recombinant production. On the other hand, Losac has no homology to known proteases, but it can be inhibited by PMSF, a serine protease inhibitor. Instead, it shows closer homology to members of the hemolin family of proteins, a group of cell adhesion molecules. The recombinant protein (rLosac) shortened the coagulation time of normal and deficient plasmas, whereas it was ineffective in factor X-deficient plasma unless reconstituted with this protein. rLosac was able to activate factor X in a dose- and time-dependent manner but not ã-carboxyglutamic acid domainless factor X. Moreover, phospholipids and calcium ions increased rLosac activity. Also, rLosac had no effect on fibrin or fibrinogen, indicating its specificity for blood coagulation activation. Linear double reciprocal plots indicate that rLosac follows a Michaelis-Menten kinetics. Cleavage of factor X by rLosac resulted in fragments that are compatible with those generated by RVV-X (a well known factor X activator). Together, our results validate Losac as the first protein from the hemolin family exhibiting procoagulant activity through selective proteolysis on coagulation factor X.

Deficiência congênita de fator X: quando pensar? / Congenital factor X deficiency: when thinking?

Objetivo: Descrever o caso de um lactente portador de deficiência congênita de fator X e discutir o diagnóstico diferencial dessa coagulopatia rara. Relato do caso: Lactente, 54 dias de vida, sexo masculino, foi encaminhado paraavaliação hematológica devido a episódios prévios de hemorragia de etiologia a esclarecer. No segundo dia de vida, apresentou epistaxe e aumento do perímetro cefálico e, na segunda semana de vida, apresentou enterorragia. Foram realizados examesque evidenciaram TP e TTPA prolongados e antecedentes familiares sugestivos de diátese hemorrágica. Em nosso serviço, foram descartadascausas adquiridas que poderiam justificar o prolongamento dos tempos de coagulação (deficiência de vitamina K, infecção, hepatopatias) e também foram descartados sangramentos emoutros locais (sistema nervoso central e abdome). As dosagens dos fatores de coagulação II e V foram normais, sendo detectados níveis de fator X inferioresa 1% (FX < 1%), evidenciando deficiência grave desta proteína. Durante a investigação, o paciente apresentou novo episódio de enterorragia, sem descompensação hemodinâmica e recebeu plasma fresco congelado. Atualmente, está em seguimento ambulatorial, em uso profilático de concentrado de complexo protrombínico, sem manifestaçõeshemorrágicas. Conclusão: As coagulopatias congênitas são doenças hemorrágicas resultantes da deficiência quantitativa ou qualitativa de umaou mais das proteínas plasmáticas da coagulação. Os pacientes acometidos podem apresentar sangramentos de gravidade variável, espontâneosou pós-traumáticos, presentes ao nascimento ou diagnosticados ocasionalmente. Estas coagulopatiassão caracterizadas por herança genética, quadro clínico e laboratorial distintos entre si e, entre elas, as hemofilias e a doença de Von Willebrand são as mais comuns. São consideradas coagulopatias raras as deficiências de fatores I, II, V,...

Objective: To describe the case of an infant with congenital factor X deficiency and to discuss the differential diagnosis of other rare coagulopathies. Case report: Infant, 54-day-old male was referred for hematologic evaluation due to previous episodes of bleeding of unknown etiology. On the second day of life, he had epistaxis and increased head circumference and, in the second week of life, had rectal bleeding. Laboratory assays were performed and showed prolonged PT and APTT and family history suggestive of bleeding disorders. In our department, other acquired causes that could justify the prolongation of clotting time (vitaminK deficiency, infection, liver disease) were excluded and bleeding were also evaluated at other sites (central nervous system and abdomen). The levels of coagulation factors II and V were normal and detected levels of factor X less than 1% (FX<1%),suggesting serious deficiency of this protein. During the investigation, the patient presented a new episode of rectal bleeding, without hemodynamicinstability, and received fresh frozen plasma. He is currently in follow-up, receiving prophylactic prothrombin complex concentrate, without hemorrhagic manifestations. Conclusion: the congenital coagulopathies are bleeding disorders resulting from a quantitative or qualitative deficiency of one or more of the plasma procoagulant protein. The affected patients may have bleeding of varying sev rity, spotaneous or post traumatic, present at birthor diagnosed occasionally. These bleding disorders are characterized by specific genetic inheritance and clinical and laboratory characteristics. Amonginherited bleedingdisorders, the hemophilia and Von Willebrand disease are the most common. The deficienciesof factors I, II, V, VII, X and XIII are considered rare coagulation disorders and the differential diagnosis among these diseases is essential to guideappropriate therapy. In cases of severe deficiency of factor X, as patients may have...

Anti-Xa e antitrombínicos específicos nas síndromes isquêmicas miocárdicas instáveis com e sem supradesnível do segmento ST / Factor Xa inhibitors and selective antithrombin agents in acute coronary syndromes

As síndromes isquêmicas miocárdicas instáveis incluem um amplo espectro de manifestações da doença coronária, variando de angina instável e infarto do miocárdio sem supradesnível do segmento ST até infarto do miocárdio com dupradesnível do seguimento ST. O mecanismo fisiopatológico subjacente envolve a combinação de aterosclerose e um evento trombótico. O tratamento com heparina não fracionada ou de baixo peso molecular tem demonstrado ser eficaz e seguro nesses pacientes. Entretanto, uma limitação inerente a essas medicações é a ausência de efeito na trombina ligada ao coágulo. Novos anticoagulantes foram desenvolvidos, tendo como alvo as duas formas de trombina - livre e aquela aderida ao coágulo (inibidores diretos da trombina) - bem como outros componentes individuais da cascata de coagulação (inibidores diretos ou indiretos do fator Xa). Esses agentes anticoagulantes demonstraram resultados promissores em estudos pré-clínicos e foram avaliados em ensaios de síndromes isquêmicas agudas em grande escala. Esta revisão discute a eficácia e a segurança desses novos agentes quando comparados com os regimes que utilizam heparina como anticoagulantes de escolha.

Acute coronary syndromes include a broad spectrum of coronary artery disease ranging from unstable angina, non-ST-segment elevation myocardial infarction to ST-segment elevation myocardial infarction. The underlying pathophysiological mechanism involves a combination of atherosclerosis and a thrombotic event. Treatment with unfractionated heparin or low-molecular-weight heparin has shown to be effective and safe in these patients. However, a common limitation of these medications is the lack of effect on clot-bound thrombin. Novel anticoagulants targeted for both the free and clot-bound forms of thrombin (direct thrombin inhibitors), or other individual components of the coagulation cascade (direct or indirect factor Xa inhibitors). These anticoagulants have shown promising results in preclinical testing and have been evaluated in large-scale clinical acute coronary syndrome trials. This review discusses the efficacy and safety of these novel agents compared with heparin-based anticoagulants.

Comparative analysis of newborn and adult Bothrops jararacasnake venoms

Different clinical manifestations have been reported to occur in patients bitten by newborn and adult Bothrops jararaca snakes. Herein, we studied the chemical composition and biological activities of B. jararaca venoms and their immunoneutralization by commercialantivenin at these ontogenetic stages. Important differences in protein profiles were noticed both in SDS-PAGE and two-dimensional electrophoresis. Newborn venom showed lower proteolytic activity on collagen and fibrinogen, diminished hemorrhagic activity in mouse skin and hind paws, and lower edematogenic, ADPase and 50-nucleotidase activities. However, newborn snake venom showed higher L-amino oxidase, hyaluronidase,platelet aggregating, procoagulant and protein C activating activities. The adult venom is more lethal to mice than the newborn venom. In vitro and in vivo immunoneutralization tests showed that commercial Bothrops sp antivenin is less effective at neutralizing newborn venoms. These findings indicate remarkable differences in biological activities ofB. jararaca venom over its development. We suggest that not only venom from adult specimens, but also from specimens at other ontogenetic stages should be included in the venom pool used for raising antibodies. Thus, Bothrops antivenin can efficaciouslyneutralize proteins lacking in the adult venom pool, especially those that promote more intense hemostatic disturbances in victims of newborn snakes.

Unique strategies for therapeutic gene transfer in haemophilia A and haemophilia BWFH State-of-the-Art Session on Therapeutic Gene Transfer Buenos Aires, Argentina.

SUMMARY: Gene therapy of haemophilia has been initiated through a number of approaches including expression in muscle, liver and omental implanted fibroblasts, or i.v. injection of an expression construct under the control of a ubiquitous promoter. In all these approaches, the goal was to have factor VIII (FVIII) or factor IX (FIX) synthesized so that it restored the levels of the missing protein in blood. The three talks in this session are totally, or at least in part, directed at strategies that may be clinically effective even in the absence of correction of the missing plasma clotting factor, although the haematopoietic stem cell or blood outgrowth endothelial cell therapy could achieve plasma correction as well. Two of the approaches achieve localized coagulation factor expression without necessarily correcting the systemic defect--one is with synthesis of FVIII or FIX within the joint space and the other is with the local release of FVIII (or FIX) by platelets at the site of vascular injury. All of the three approaches have demonstrated efficacy in small animal models and are now the subject of larger animal studies. None has yet to progress to human trials.