La greffe de cellules souches hématopoïétiques est parfois le seul traitement efficace contre les cancers hématologiques ainsi que plusieurs autres désordres reliés au système hématopoïétique. La greffe autologue est souvent le traitement de choix pour les patients atteints de lymphome ou de myélome. Dans ce cas, les cellules souches hématopoïétiques (CSH) du patient sont récoltées et congelées. Le patient subit ensuite des traitements de chimiothérapie et/ou radiothérapie qui éliminent les cellules malignes, mais détruisent aussi son système hématopoïétique. Ce dernier sera ensuite reconstitué par la greffe de CSH. Ces traitements ont pour conséquence de plonger le patient en état d’aplasie pour une période variant de 2 à 4 semaines. La thrombocytopénie (faible taux de plaquettes) est une complication majeure nécessitant des transfusions plaquettaires répétées et associée à une augmentation de la mortalité hémorragique post-transplantation. Il serait particulièrement intéressant de développer une thérapie accélérant la reconstitution des mégacaryocytes (MK), ce qui aurait pour effet de raccourcir la période de thrombopénie et donc de diminuer les besoins transfusionnels en plaquettes et potentiellement augmenter la survie. HOXB4 est un facteur de transcription qui a déjà démontré sa capacité à expandre les CSH et les progéniteurs multipotents (CFU-GEMM) donnant naissance aux MK. Il est donc un bon candidat pour l’expansion des progéniteurs MK. Comme la protéine HoxB4 a par contre une courte demi-vie (~1.1h), des protéines HoxB4 de deuxième génération avec une plus grande stabilité intracellulaire ont été créées (1423 (HoxB4L7A), 1426 (HoxB4Y23A) et 1427 (HoxB4Y28A)). Nous avons donc étudié la capacité d’HoxB4 sauvage et de deuxième génération à expandre les CSH, ainsi que les MK donnant naissance aux plaquettes. La surexpression rétrovirale de ces protéines HoxB4Y23A et HoxB4Y28A conduit à une expansion des progéniteurs MK murins in vitro supérieure à HoxB4-wt, 1423 et au contrôle GFP. La reconstitution plaquettaire in vivo dans un modèle murin a ensuite été évaluée par des transplantations primaires et secondaires. Les résultats révèlent que la surexpression rétrovirale des différents HoxB4 n’apporte pas de bénéfice significatif à la reconstitution plaquettaire des souris. Lorsque cultivées dans un milieu favorisant la différenciation mégacaryocytaire, le traitement de cellules CD34+ dérivées du sang de cordon ombilical avec les protéines recombinantes TATHoxB4WT ou de seconde génération n’a pas augmenté la production plaquettaire. Par contre, de manière intéressante, les cellules CD34+ provenant de sang mobilisé de patients atteints de myélome et mises en culture dans un milieu favorisant l’expansion des CSH ont montré des différences significatives dans la différenciation des progéniteurs MK en présence de la protéine recombinante TATHoxB4. La protéine HOXB4 possède donc un avenir prometteur quant à une amélioration de l’état thrombocytopénique chez les patients. / Haematopoietic stem cell (HSC) transplantation is the most efficient treatment against a number of cancers or other disorders of the hematologic system. Prior to HSC transplantation, patients are exposed to high doses of radiotherapy and/or chemotherapy to eliminate malignant cells. However, these treatments result in a state of aplasia, particularly in thrombocytopenia, which is characterised by very low blood platelet counts. Platelets produced by megakaryocytes (MK) are essential components of the blood system and play a critical role in the prevention of bleeding. Thus a low platelet blood level is a major complication and contributes significantly to transplant related mortality. At present, regular infusion of platelets isolated from healthy donors is the treatment of choice for thrombocytopenia. However, this is cumbersome for patients as well as donors and, in many instances results in platelet refractoriness due to the generation of auto-antibodies against disparate HLA molecules expressed on donor platelets. Therefore, the development of strategies to accelerate MK production and thus platelet reconstitution post HSC transplant would represent a major advance. It has already been shown that HoxB4 expands HSC and multipotent progenitors (CFU-GEMM) that give rise to megakaryocytes (MK). Thus HoxB4 is a great candidate for in vitro MK progenitor expansion. However, the short half-life of HoxB4 protein prompted us to generate a second generation of HoxB4 proteins with greater intracellular stability. We therefore studied the capacity of wild type (WT) and HoxB4 with 3 substitutions (1423 (HoxB4L7A), 1426 (HoxB4Y23A) and 1427 (HoxB4Y28A) resulting in a longer protein half-life to expand HSC as well as MK progenitors. Retroviral-mediated expression of HoxB4Y23A and HoxB4Y28A proteins showed a greater expansion of murine MK progenitors, in comparison with HoxB4WT or HoxB4L7A proteins or GFP control. We also evaluated the ability of HSC expressing second generation HoxB4 to generate platelets in a murine model. Our results show that retroviral-mediated transduction of second generation HoxB4 in murine HSC does not provide a significant advantage over HoxB4WT in platelet reconstitution in mice. Interestingly, treatment of CD34+ cells derived from cord blood showed only marginal effect of HoxB4WT or second generation HoxB4 soluble recombinant proteins when cultured under conditions optimized for megakaryocyte differentiation. Unexpectedly, CD34+ cells derived from mobilized peripheral blood of myeloma patients showed a significant increase in MK progenitor differentiation in the presence of TAT-HoxB4WT when cultured in expansion medium for HSC. Thus, HoxB4 holds promise in autologous HSC transplantation for the treatment of thrombocytopenic patients.

The overall aim of this thesis is to improve knowledge about the prevention of infectious and bleeding complications in patients with hematological malignancies, primarily in those with chronic lymphocytic leukemia (CLL) and myelodysplatic syndrome (MDS). Hypogammaglobulinemia, impaired production of immunoglobulins (Ig), is an established risk factor for infection, but the impact of IgG pure subclass deficiency (IgG subclass deficiency with adequate production of IgG, IgA, and IgM) has been debated. In a retrospective single institution study, we concluded that pure IgG subclass deficiency in CLL patients is rare and is not associated with an increased risk of infection. Hence, routine analysis of IgG subclasses in patients with CLL is not warranted. There is no consensus on recommending vaccination against Streptococcus pneumoniae to CLL patients mainly because comparative studies are lacking. In our randomized trial, the efficacy of a conjugated pneumococcal vaccine on immune response was superior or equal to a polysaccharide vaccine for all pneumococcal serotypes common for the two vaccines. A conjugate pneumococcal vaccine should therefore be included in vaccination programs for patients with CLL. Bronchoalveolar lavage (BAL) is a well-established invasive method to identify the cause of pulmonary infiltrates in immunocompromised patients. In a retrospective trial, we have studied the diagnostic yield of BAL in patients with hematological malignancies. We concluded that BAL is highly useful in either verifying or excluding some of the important respiratory tract infections affecting these patients, particularly invasive pulmonary aspergillosis (IPA) and Pneumocystis jirovecii pneumonia (PJP). However, standardized procedures for BAL sampling should be continually revised to avoid unnecessary microbiological tests. Thrombocytopenia, an adverse prognostic factor in patients with MDS, can be aggravated by azacitidine, first-line treatment for high-risk MDS. Eltrombopag, a thrombopoietin-receptor agonist (TPO-R), alleviates thrombocytopenia in patients with immune thrombocytopenic purpura (ITP). In a phase I clinical trial, we concluded that the combination of eltrombopag and azacitidine in high-risk MDS patients with thrombocytopenia is feasible and well tolerated in doses up to 200 mg eltrombopag daily.

Introdução: Trombocitopenia é a redução dos níveis plaquetários ocasionada por diversas condições, como hepatopatias e a Trombocitopenia Imune (TI), por exemplo. A redução de plaquetas na hepatopatia pode ocorrer devido à deficiência medular por hipovitaminose, aumento do consumo celular e hiperesplenismo e/ou devido à coagulação intravascular disseminada. Na Trombocitopenia Imune, a redução plaquetária ocorre tanto por maior destruição destas células quanto por diminuição medular de sua produção. Portadores de trombocitopenia podem apresentar achados orais como petéquias e/ou equimoses e sangramento gengival, espontâneo ou provocado. Procedimentos cirúrgico-odontológicos nestes pacientes devem ser realizados com cautela, após avaliação do seu quadro clínico e, preferencialmente, por profissional especializado. Muita controvérsia ainda existe em relação à abordagem cirúrgico-odontológica destes pacientes tanto em relação aos níveis plaquetários, quanto em relação à reposição plaquetária prévia, não havendo ainda, um protocolo internacionalmente estabelecido. Diversos métodos hemostáticos locais auxiliam durante este tipo de abordagem, sendo o agente a base de quitosana um dos métodos que têm se mostrado efetivo em diversos estudos e apresenta-se, ainda, menos oneroso que o selante de fibrina, por exemplo, um dos métodos mais utilizados. Objetivo: Desta forma, o objetivo desta pesquisa foi observar e descrever o desempenho clínico do agente a base de quitosana em pacientes com contagem plaquetária <= a 30.000/mm3 (Grupo Quitosana) submetidos a exodontias unitárias, utilizando como padrão de comparação o grupo de pacientes trombocitopênicos com contagem plaquetária entre 31.000 e 50.000/mm3 (Grupo Controle), submetidos a exodontias unitárias, sem o uso do curativo hemostático a base de quitosana e ainda, descrever o atendimento odontológico a pacientes com contagem plaquetária inferior a 50.000/mm3 . Casuística e métodos: Pacientes trombocitopênicos com contagem abaixo de 50.000/mm3 foram submetidos a exodontias unitárias, estando divididos em Grupo Quitosana(GQ):pacientes com plaquetas abaixo de 30.000/mm3, que receberam o agente a base de quitosana após a extração e, Grupo Controle(GC): pacientes com plaquetas entre 31.000/mm3 e 50.000/mm3 e que não receberam o agente a base de quitosana. O sangramento foi observado 7 dias após a exodontia através do Índice de Sangramento Alveolar Pós- Exodontia (ISAPE) e para análise estatística foi utilizado o programa SPSS (Statistical Package for Social Sciences) 20.0; nível de significância de 5% (p=0,05), e realizado o teste de Mann-Whitney, análise de Correlação de Spearman e, teste do Chi-Quadrado e Fator de risco com intervalo de confiança (IC) de 95%. Resultados: Foram realizadas 41 exodontias unitárias entre 03/2011 e 09/2012. A média de idade dos pacientes estudados foi de 46,58 ±10,87anos, com mediana de 48,50 (variando de 20 a 64). Dentre eles, 51,20% (n=21) eram do gênero feminino e 48,79% (n=20) do masculino. 21 procedimentos foram incluídos no GQ e, 20 procedimentos, no GC. O GQ apresentou contagem plaquetária entre 5.000 e 30.000/mm3 e ISAPE médio de 0,10; sendo que 2 (9,52%) pacientes tiveram ISAPE acima de zero. Já o GC apresentou plaquetas entre 31.000 e 50.000/mm3, ISAPE médio de 0,40 e 6 (30%) pacientes com ISAPE acima de zero. Não houve significância estatística em relação ao ISAPE. Discussão: Até o presente momento não foram encontrados outros trabalhos nos moldes da presente pesquisa nas bases de dados pesquisadas (Lilacs, Medline, Bireme). Inúmeros trabalhos buscam estabelecer a contagem plaquetária mínima necessária para um paciente ser submetido à cirurgia odontológica e ainda, quando será indicada reposição plaquetária prévia. Em ambos os aspectos a literatura se mostra controvérsia, havendo autores que indicam reposição plaquetária prévia a pacientes com plaquetas em torno de 100.000/mm3, e autores que relatam que cirurgias orais simples, como as exodontias unitárias, podem ser realizadas de forma segura sem reposição plaquetária em pacientes com plaquetas em torno de 30.000/mm3. Não existe atualmente um protocolo de atendimento estabelecido internacionalmente. O ISAPE não apresentou significância estatística entre os grupos estudados, aspecto possivelmente influenciado pela heterogeneidade dos grupos e/ou ainda, pelo número reduzido da amostra. Porém, a porcentagem dos pacientes que apresentaram ISAPE maior que 0 mostra efetividade do agente hemostático em 90,48% do GQ, concordando com Belman et al.(2006), Brown et al.(2007) e Wedmore et al.(2006) que mostram 80,0%, 79,0% e 97,0%, respectivamente. Conclusão: Não houve diferença estatística entre os grupos em relação ao desempenho clínico hemostático do curativo a base de quitosana. Foi possível descrever o protocolo de atendimento a pacientes trombocitopênicos efetivo e resolutivo, já utilizado rotineiramente na Divisão de Odontologia HC-FMUSP / Introduction: Thrombocytopenia is an abnormally low amount of platelets caused by many conditions as liver disorders and immune thrombocytopenia for example. The reduction of platele count in liver disorders may be caused by bone marrow deficiency due to hypovitaminosis, hypersplenism and disseminated intravascular coagulation while in immune thrombocytopenia may be caused by greater desctruction of these cells or its diminished production by the bone marrow. Patients with thrombocytopenia may present oral manifestations as petechiae and/or ecchymosis and provoked/spontaneous gingival bleeding. In these patients, surgical dental procedures should be performed with caution and only after a detailed medical assessment, preferably performed by a specialist. The dental management of patients with thrombocytopenia is still controversial regarding the amount of platelets and the need of platelet infusion prior to these procedures. To this date, no clinical guidelines has been developed regarding the dental management of patients with thrombocytopenia. Many hemostatic agents has been used to control post surgical bleeding. Many studies had shown thay chitosan is effective and cheaper than fibrin sealant, one of the most popular hemostatic agents. Objetive: This study was design to assess the effect of chitosan as a local haemostatic agent in patients with platelet count <= 30.000/mm3 compared to patients with thrombocytopenia and platelet count of 31.000/mm3 to 50.000/mm3 submitted to single dental extraction and to describe the protocol for dental treatment of patients with platelet count lower than 50.000/mm3 in a tertiary health science center. Methods: Patients with thrombocytopenia with platelet count lower than 50.000/mm3 were assessed. Patients with platelet count lower than 30.000/mm3 (study group) and patients with platelet count of 31.000/mm3 to 50.000/mm3 (control group) were submitted to single dental extraction. Chitosan was used only in the study group and no other type of hemostatic agent was used in the control group. Bleeding was measured according to the post dental extraction index (ISAPE) seven days after dental extraction. The results were statistically analyzed using the Statistical Package for Social Sciences (SPSS) 20.0 program. For statistical analysis, the Mann-Whitney test, Chi-square test, Spearman\'s rank correlation coeficient and confidence interval for relative risk (95%) were used. P< 0.05 was considered statistically significant. Results: Forty-one single dental extractions were performed between March/2011 and September/2012. The mean age of patients was 46,58 ±10,87 years of age. Median was 48,50 ranging from 20 to 64 years of age. Fifty-one percent (n=21) were females and 48,79% (n=20) males. Twenty-one extarctions were performe in the Chitosan group and 20 in the control group. Chitosan group presented platelet count of 5.000 to 30.000/mm3 and mean ISAPE médio of 0,10; where two patients (9.52%) had ISAPE greater than zero Control group presented with platelet count of 31.000 to 50.000/mm3, mean ISAPE of 0,40 and six patients (30%) with ISAPE greater than zero. No statistical significance was related to the ISAPE between groups. Discussion: The dental management of patients with thrombocytopenia is still controversial regarding the amount of platelets and the need of platelet infusion prior to these procedures. To this date, no clinical guidelines has been developed regarding the dental management of patients with thrombocytopenia. Many studies have tried to establish the minimal platelet count and the need of platelet infusion prior to oral surgery. Unfortunately, the scientific literature is controversial. Some authors recommend platelet infusion prior to oral surgery in patients with platelel count of 100.000/mm3 while others report that single extractions can be performed safely in patients with platelet count 30.000/mm3. In our study, the ISAPE was not stastistically diferent between groups, what may be explained by the heterogenicity of patients in both groups and by the small sample. However, the greater amount of patients (90%) who presented ISAPE greater 0 showed the effectiveness of chitosan as a hemostatic agent in agreement with previous authors as Belman et al.(2006), Brown et al.(2007) e Wedmore et al.(2006) that presented 80,0%, 79,0% e 97,0%, respectively. Conclusion: No difference was found regarding the effectiveness of chitosan as hemostatic agent between groups. A clinical guideline was developed on dental management of patients with thrombocytopenia and since then it has been used daily at the Department of Dentistry HC-FMUSP

Pacientes envenenados pela serpente Bothrops jararaca manifestam uma tendência hemorrágica em que a plaquetopenia é um achado consistente. Manifestações clínicas sistêmicas, como sangramento de mucosas e microangiopatia trombótica em alguns pacientes, apresentam similaridades com sinais clínicos de doença de von Willebrand e púrpura trombocitopênica trombótica. Algumas proteínas do veneno - como a botrocetina (uma proteína relacionada às lectinas do tipo C) e as metaloproteinases do veneno (SVMP) - interferem direta ou indiretamente na interação entre plaquetas e o fator de von Willebrand (vWF) in vitro e in vivo. E dessa forma, podem contribuir para os sangramentos induzidos pelo envenenamento devido à importância que o vWF tem para a hemostasia primária. Pensando em compreender a participação do vWF do organismo e a botrocetina e as SVMP do veneno bruto de B. jararaca (BjV) na plaquetopenia induzida pelo envenenamento, utilizamos dois modelos experimentais: ratos Wistar heterogênicos e camundongos nocautes do gene Vwf (Vwf-/-). No modelo em ratos, o BjV foi pré-incubado com salina (controle positivo), um inibidor de metaloproteinases (Na2-EDTA), anticorpos policlonais anti-botrocetina, glicerol (veículo dos anticorpos), ou a combinação do Na2-EDTA e anticorpos anti-botrocetina; o grupo controle negativo foi injetado somente com salina. Após a administração subcutânea (s.c.) dos venenos tratados (1,6 mg/kg), amostras de sangue foram coletadas após 3, 6 ou 24 h, e analisaram-se a contagem de plaquetas, quantificação antigênica (vWF:Ag) e da atividade de ligação do vWF ao colágeno (vWF:CB), a atividade de ADAMTS13, a distribuição multimérica de vWF, e a atividade coagulante de fator VIII (FVIII). Para explorar a participação do vWF na plaquetopenia, camundongos nocautes de vWF (Vwf-/-) e camundongos controles (C57BL/6) foram injetados s.c. com BjV incubado com salina (grupo positivo do envenenamento) ou apenas salina (grupo controle negativo). As injeções dos tratamentos, bem como os períodos analisados foram idênticos aos dos ratos. Em nossos resultados, todos os ratos injetados com algum tratamento de BjV, inclusive nos animais que receberam veneno pré-tratado com anticorpo anti-botrocetina e/ou Na2-EDTA, apresentaram plaquetopenia, com maior intensidade em 6 h. Na avaliação do vWF foi encontrada uma grande variação individual nos grupos de tratamentos, porém ainda assim houve uma tendência a redução nos níveis de vWF:Ag em 3 e 6 h nos ratos que receberam BjV sem inibidores. A administração de BjV tratado somente com anticorpo anti-botrocetina promoveu uma maior redução nos níveis de vWF:Ag em 3 h, com retorno aos níveis semelhantes aos de controle negativo em 6 h e 24 h. A inibição sozinha das metaloproteinases não promoveu efeito importante, porém em 6 h, potencializou a ação do anticorpo anti-botrocetina na inibição conjunta do decréscimo de vWF:Ag e vWF:CB. A análise dos multímeros do vWF mostrou perfis bastante variáveis individualmente, porém os multímeros de alto peso molecular e intermediário tenderam a diminuir e os de baixo peso a aumentar nos animais que receberam algum tratamento com BjV, especialmente em 24 h. Na dosagem de FVIII, houve redução em 3 e 6 h em todos os ratos que receberam qualquer tratamento de BjV, sem grandes variações entre esses grupos. A atividade de ADAMTS13 apresentou uma redução dos valores em 3 e 6 h, que foi revertida pela inibição das metaloproteinases do veneno. Já nos camundongos, a plaquetopenia esteve presente em todos os animais nocautes e controles que receberam BjV, mostrando ser independente da presença de vWF. Nos camundongos controles (C57BL/6), não houve alterações evidentes em vWF:Ag durante o envenenamento, porém em 3 h houve uma tendência a sua diminuição. Em conjunto, nossos resultados mostram que a presença da botrocetina no veneno bruto não afeta a plaquetopenia desencadeada pelo envenenamento, porém influencia o vWF plasmático quantitativa e funcionalmente. As metaloproteinases do veneno têm forte efeito sobre a enzima fisiológica reguladora da atividade biológica do vWF, a ADAMTS13, que indiretamente pode afetar os níveis de vWF. Ademais, a intensidade da plaquetopenia durante o envenenamento de B. jararaca não depende da presença de vWF, e tendo em conta o caráter multifatorial do consumo plaquetário durante o envenenamento, sugerimos que outros mecanismos possam ser responsáveis pela plaquetopenia induzida pelo BjV. Com isso, concluímos que o consumo de vWF no envenenamento por B. jararaca é um fator contribuinte, porém não determinante, para as alterações da contagem plaquetária / Patients bitten by Bothrops snakes manifest a bleeding tendency in which thrombocytopenia is consistently observed. Systemic clinical manifestations, such as mucous bleeding and thrombotic microangiopathy in some patients, share similarities with symptoms of von Willebrand disease and thrombotic thrombocytopenic purpura. Some venom proteins - e.g. botrocetin (a C-type lectin-related protein) and snake venom metalloproteinases (SVMP) - disturbs, direct or indirectly, the interaction between platelets and von Willebrand factor (vWF) in vitro and in vivo, and may contribute thereby to snakebite-induced bleedings, once vWF is required for primary hemostasis. To better understand the relation between plasma vWF, and botrocetin and SVMPs from B. jararaca crude venom (BjV) in the thrombocytopenia induced by envenomation, we used two experimental models: Wistar heterogenic rats and vWF knockout mice (Vwf-/-). In the rat model, BjV was pre-incubated with saline (positive control), metalloproteinase inhibitor (Na2-EDTA), polyclonal anti-botrocetin antibodies, glycerol (antibody vehicle), or the combination of Na2-EDTA and anti-botrocetin antibodies; the negative control group was injected with saline only. After subcutaneous injection (s.c.) of treated venom (1.6 mg/kg), blood samples were collected after 3, 6 or 24 h, and platelet count, vWF antigen (vWF:Ag) and collagenbinding activity (vWF:CB), ADAMTS13 activity, vWF multimer distribution, and factor VIII (FVIII) coagulant activity were analyzed. To investigate the participation of vWF in thrombocytopenia, vWF knockout mice (Vwf-/-) and control mice (C57BL/6) were injected s.c. with saline only (negative control group) or BjV pre-incubated with saline (positive control group). The same protocols used for rats were accomplished in mice. Our results showed that all rats injected with any BjV treatment, including animals which received anti-botrocetin antibodies and/or Na2-EDTA-treated BjV, showed thrombocytopenia, with the nadir at 6h. vWF analysis exhibited a large individual variation among treatment groups, but there was a tendency to reduce vWF:Ag levels at 3 and 6 h in rats that received BjV pre-incubated with saline (without any inhibitor). Administration of BjV pre-incubated only with anti-botrocetin antibodies evoked a large reduction in vWF:Ag levels at 3 h, which returned to levels similar to those of the negative control group at 6 and 24 h. SVMP inhibition alone did not induce an important effect, but potentialized the activity of anti-botrocetin antibodies to inhibit the fall in both vWF:Ag and vWF:CB levels at 6 h. VWF multimer analysis had a large individual profile variation, although animals that received any BjV treatment tended to decrease the high and intermediate molecular weight multimers and to increase the low ones, especially at 24 h. FVIII showed diminished levels in all rats that received any BjV treatment at 3 and 6 h, without important variations among groups. Decreased levels of ADAMTS13 activity were noticed at 3 and 6 h, which were reverted by SVMP inhibition. In mice, thrombocytopenia was present in all control and knockout mice that received BjV, demonstrating independence of vWF presence. In control mice (C57BL/6), there were no relevant alterations in vWF:Ag during envenomation, although at 3 h there was a tendency to decrease it. Al together, our results showed that botrocetin present in crude venom does not affect thrombocytopenia induced by envenomation, but it changes the levels and function of plasma vWF. SVMP had a marked effect in ADAMTS13, the physiological enzyme that regulates vWF biological activity, which may affect vWF levels indirectly. In addition, thrombocytopenia during B. jararaca envenomation is independent of vWF, and considering the multifactorial features of platelet consumption during envenomation, we suggest that other mechanisms might account for BjV-induced thrombocytopenia. Therefore, we conclude that vWF consumption during B. jararaca envenomation is an ancillary mechanism, but not the main one to decrease platelet counts

INTRODUÇÃO: Dengue é uma doença viral prevalente e potencialmente fatal associada à alteração da permeabilidade capilar e coagulopatia. Entretanto, não há estudos concernentes aos achados tromboelastométricos nesta doença. Realizamos o presente estudo para analisar pacientes com dengue e plaquetopenia por meio de um exame rápido, efetivo e a beira leito comparando com os exames convencionais de coagulação. MÉTODOS: Trata-se de um estudo observacional e transversal conduzido entre os dias 6 de abril a 5 de maio de 2015, em São Paulo, Brasil, durante epidemia de dengue. Foi realizado tromboelastometria ROTEM® em 53 pacientes com dengue e trombocitopenia em associação com exames convencionais de coagulação: tempo de protrombina (TP), international normalized ratio (INR), tempo de tromboplastina parcial ativado (TTPa), tempo de trombina (TT), contagem de plaquetas, fibrinogênio e d-dímero. Um grupo controle de pacientes foi estabelecido para comparação do status tromboelastométrico. RESULTADOS: Um total de 38 pacientes de 53 (71,7%) apresentaram anormalidades no INTEM e 29/53 (57,4%) no EXTEM. Em contrapartida, alterações no FIBTEM foram encontradas apenas em 3/53 (5,7%). Houve significância estatística em pacientes correlacionando alterações tromboelastométricas no EXTEM e INTEM e contagem de plaquetas (p=0,052) e (p=0,005), respectivamente; assim como os valores de fibrinogênio (p=0,006) e (p=0,021), respectivamente. O grupo controle (GC) apresentou status tromboelastométrico normal em 10/10 (100%) na análise do INTEM, EXTEM, FIBTEM. Avaliação do EXTEM demonstrou significância estatística entre o GC e o grupo Dengue: CT (p=0,044); CFT (p<0,001); MCF (p < 0,001) e Alpha (p < 0,001). Foram observados níveis normais de fibrinogênio (mediana: 290) e altos níveis de d-dímero (mediana: 1330) com IQR (800-1840). Todos os pacientes (53/53) apresentavam trombocitopenia abaixo de 100 x 109/L (mediana 77 x 109/L) IQR (63-88). Exames convencionais de coagulação revelaram-se completamente normais: TP (mediana: 100%) IQR (90-100); INR (mediana: 1,0) IQR (1,0-1,1); TTPa (mediana: 28,9 segundos) IQR (26,0-32,5) e TT (mediana: 18,2 segundos) IQR (17,0-19,5). Apenas (7/49) 14,3% pacientes apresentaram sangramento e (3/52) 5,8% necessitou de hospitalização. Não houve associação entre alterações tromboelastométricas com sangramento ou hospitalização. CONCLUSÕES: Dengue representa um processo inflamatório intenso, mantendo níveis normais de fibrinogênio. Portanto, FIBTEM mantém-se normal promovendo boa formação do coágulo sem risco imediato de sangramento. Não houve correlação entre os achados tromboelastométricos com os exames convencionais de coagulação, sugerindo que testes viscoelásticos são exames mais sensíveis para análise de coagulopatia precoce nessa população / INTRODUCTION: Dengue is a prevalent and potentially fatal viral disease associated with plasma leakage and coagulopathy, though no information is available on thromboelastometric profile. We performed this study to analyze dengue fever patients with thrombocytopenia clot changes through point-ofcare thromboelastometry tests and standard coagulation tests. METHODS: This was an observational, transversal and cross sectional study conducted between April 6th and May 5th 2015 in São Paulo, Brazil, during a dengue outbreak. Thromboelastometry ROTEM® was performed in 53 patients with dengue and thrombocytopenia, in association with conventional coagulation tests: prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time (TT); platelet count, fibrinogen level, and d-dimer. A control group of 10 patients was established to compare thromboelastometry profiles. RESULTS: A total of 38 patients in 53 (71,7%) had abnormalities in INTEM, 29 in 53 (57,4%) in EXTEM. Conversely, FIBTEM was abnormal in 3/53 (5,7%). Statistical analysis revealed significant relation in those patients with impairment EXTEM and INTEM with lowered platelet (p=0,052) and (p=0,005) respectively and lowered fibrinogen levels (p=0,006) and (p=0,021) respectively. Control group (CG) had normal status in 10/10 (100%) of INTEM, EXTEM, FIBTEM analysis. EXTEM analysis demonstrated statistical differences between CG and dengue group: CT (p=0,044); CFT (p < 0,001); MCF (p < 0,001) and Alpha (p < 0,001). Normal levels of fibrinogen (median: 290) and high levels of ddimer (median: 1330) IQR (800-1840) were found. All patients (53/53) had platelet under 100 x 109/L (median 77 x 109/L) IQR (63-88). Standard coagulation tests were completely normal: PT (median: 100%) IQR (90-100); INR (median: 1,0) IQR (1,0-1,1); aPTT (median: 28,9 seconds) IQR (26.0- 32,5) and TT (median: 18,2 seconds) IQR (17,0-19.5). Only (7/49) 14,3% patients had bleeding manifestations and (3/52) 5,8% needed hospitalization. There was no association between altered thromboelastometry with bleeding manifestations or hospitalization. CONCLUSIONS: Dengue represents an intense inflammatory process, maintaining normal levels of fibrinogen. FIBTEM remains normal providing good clot strength without immediate bleeding risk. There were no correlation between thromboelastometry findings and standard coagulation exams, suggesting that viscoelastic tests are more sensible method to analyze early coagulation impairments in this population

Trombocitopenia e diminuição da função plaquetária são achados comuns em pacientes picados por serpentes do gênero Bothrops. Sabe-se que o veneno de Bothrops jararaca (VBj) apresenta compostos com características pró e anti-agregantes plaquetárias, porém existem poucos estudos sobre a influência do veneno total assim como das principais famílias de proteínas que o compõem sobre as funções plaquetárias. A utilização de modelos experimentais é essencial para entender as desordens plaquetárias em humanos que culminam em sangramentos diversos. Portanto, o objetivo deste estudo foi (i) comparar as respostas ex vivo de plaquetas lavadas de humanos e de camundongos frente ao VBj, assim como entender a participação de serinaproteinases (SVSP) e metaloproteinases (SVMP) presentes no veneno sobre a agregação dessas plaquetas; e (ii) delimitar dentro do complexo proteico do veneno os compostos que induzem a trombocitopenia em camundongos após 3 horas do início do envenenamento botrópico. As plaquetas lavadas de humanos e camundongos BALB/c, C57BL/6 e do mutante natural pérola (Ap3b1-/-) apresentaram respostas de agregação máxima ao VBj na concentração de 24,4 ?g/mL, porém esta concentração provocou uma agregação menos intensa em plaquetas humanas quando comparada àquela observada nas linhagens BALB/c e C57BL/6. Mesmo em plaquetas de camundongos pérolas, deficientes em corpos densos plaquetários, o VBj se mostrou um potente agonista, promovendo a agregação plaquetária sem a necessidade da secreção do conteúdo granular. A ação agonista do veneno promoveu a secreção de ATP presente nos corpos densos plaquetários de humanos e das linhagens BALB/c e C57BL/6 de forma tão intensa quanto à provocada pela trombina, assim como a secreção de PF4 presente nos grânulos ? de plaquetas humanas e de camundongos BALB/c. Já em relação à secreção lisossomal, observou-se que as plaquetas humanas secretam níveis mais baixos de ?-hexosaminidase quando estimuladas com VBj do que pela trombina, enquanto que em plaquetas de camundongos BALB/c a secreção lisossomal ao VBj foi superior à constatada com a trombina. Os baixos níveis de lactato desidrogenase (LDH) no sobrenadante das plaquetas estudadas mostraram ausência de atividade direta citotóxica pelo VBj. Para verificar se as principais classes de famílias de enzimas do VBj, SVMP e SVSP, estavam envolvidas na ativação plaquetária ex vivo, elas foram inibidas com Na2EDTA (13 mM) e AEBSF (8 mM), respectivamente. Observou-se que em plaquetas humanas as serinaproteases são importantes para a agregação ex vivo, enquanto a agregação das plaquetas de camundongos BALB/c foi independente dessa classe de toxinas. Os resultados dos ensaios in vivo demonstraram que as proteínas do VBj com peso molecular inferior a 50 kDa (UF < 50 kDa) são importantes para o estabelecimento da trombocitopenia em camundongos BALB/c que receberam essa fração por via subcutânea e que esse quadro é independente de manifestações hemorrágicas e do desenvolvimento de coagulopatia durante o envenenamento botrópico. A caracterização dos compostos presentes no UF < 50 kDa foi realizada por espectrometria de massas e foi observada a presença predominante de metaloproteinases (37%) e proteínas similares às lectinas do tipo-C (33%), enquanto serinaproteases (17%), fosfolipases A2 (10%) e outros compostos (3%) somaram 30% da fração UF < 50 kDa. Em conclusão, o veneno é um potente agonista plaquetário que promove agregação, aglutinação e secreção de plaquetas humanas e de camundongos, independente da secreção de corpos densos plaquetários, e a fração do veneno responsável pela trombocitopenia em camundongos BALB/c tem peso molecular menor que 50 kDa / Thrombocytopenia and platelet dysfunction are common findings in patients bitten by Bothrops jararaca snakes. Pro- and anti-aggregating toxins have been isolated from Bothrops jararaca venom (BjV), but only few studies have been carried out about the effects of crude BjV and its main families of enzymes on platelet function ex vivo, as well as to understand their relevance to the pathophysiological events that occur during B. jararaca envenomation. Animal models have been used to understand platelet disorders in humans that culminate in bleeding manifestations. Thus, the aim of this study was to investigate (i) the effects of BjV, and snake venom serine proteinases (SVSP) and snake venom metalloproteinases (SVMP) contained therein, on aggregation and secretion in suspensions of washed human and mouse platelets, and (ii) to determine the BjV fractions, obtained by ultrafiltration, that induce thrombocytopenia in BALB/c mice after 3 h of administration of Bothrops envenomation. Washed platelets from humans and BALB/c, C57BL/6 and pearl (Ap3b1-/-) mice showed maximal aggregation responses to BjV at the concentration of 24.4 ?g/mL. However, this concentration aggregated less intensely platelets from humans than BALB/c or C57BL/6 mice. Even in pearl mouse platelets, which are deficient in dense bodies, BjV proved to be a potent agonist, promoting platelet aggregation without the requirement of granule content secretion. Nonetheless, BjV induced secretion of ATP, present in dense bodies, and PF4, present in ? granules, in the same extent as thrombin, from platelets of humans and mice. In regard to lysosomal secretion, it was observed that human platelets secreted low ?-hexosaminidase levels when stimulated by BjV than thrombin, whereas in BALB/c platelets higher secretion was induced by BjV than by thrombin. Release of lactate dehydrogenase (LDH) was similar between BjV and thrombin, evidencing the absence of cytotoxic activity by BjV on platelets. Inhibition of SVMP and SVSP, using Na2EDTA (13 mM) and AEBSF (8 mM), respectively, demonstrated that SVSP are important for ex vivo aggregation only in human platelets, whilst BALB/c platelet aggregation was independent of both of them. In in vivo studies, only BjV toxins with molecular weight less than 50 kDa (UF50) caused thrombocytopenia when administered s.c. to BALB/c mice, and it was independent of hemorrhagic manifestations and consumptive coagulopathy. Characterization by mass spectrometry of these toxins present in UF50 showed the predominant presence of SVMP (37%) and type-C lectin proteins (33%) were observed, while SVSP (17%), phospholipases A2 (10%) and other proteins (3%) accounted for the remaining toxins in UF50. In conclusion, BjV is a potent platelet activating agent that promotes aggregation, agglutination and secretion of human and mouse platelets, independent of secretion of dense platelet bodies, and the fraction of venom responsible for thrombocytopenia in BALB / c mice has a molecular weight less than 50 kDa

In this study, we demonstrated that membrane immunofluorescence (MIF) with canine erythrocytes is a much more sensitive diagnostic technique compared with the Coombs test to detect auto-antibodies on RBC. We also demonstrate how the evaluation of the MIF test can be made more precisely which results in a more clear interpretation. Till nowadays the Evans syndrome (combined thrombocytopenia and anemia) is not very well diagnosed in dogs. Only a few studies with low animal numbers tested auto-antibodies on RBC and thrombocytes. Here we describe the frequency of Evans syndrome based on the evaluation of a large data set with 557 dogs. The novelty of the thesis also lies in making a research of the amount of CICs in sera of AIHA/AITP patients is described as well as the cytotoxic potential of patient’s sera for canine leucocytes. These new aspects of diagnosis (AIHA) and pathogenesis (AIHA/AITP) are not only relevant for dogs but also for humans and can be used for better differential diagnosis in medicine. The new findings with respect to circulating immune complexes and cytotoxicity are also offer new therapeutic concepts. Besides, the study has resulted in the characterization of monoclonal antibodies which allow for the detection of so far undetectable canine differentiation antigens (CD molecules) on canine erythrocytes (CD235) and thrombocytes (CD42a). The identified mAbs are useful in the identification of relevant target structures for autoantibodies on these cells.

General attrition rates in drug development pipeline have been recognized as a necessity to shift gears towards new methodologies that allow earlier and correct decisions, and the optimal use of all information accrued throughout the process. The quantitative science of pharmacometrics using pharmacokinetic-pharmacodynamic models was identified as one of the strategies core to this renaissance. Coupled with Optimal Design (OD), they constitute together an attractive toolkit to usher more rapidly and successfully new agents to marketing approval. The general aim of this thesis was to investigate how the use of novel pharmacometric methodologies can improve the design and analysis of clinical trials within drug development. The implementation of a Monte-Carlo Mapped power method permitted to rapidly generate multiple hypotheses and to adequately compute the corresponding sample size within 1% of the time usually necessary in more traditional model-based power assessment. Allowing statistical inference across all data available and the integration of mechanistic interpretation of the models, the performance of this new methodology in proof-of-concept and dose-finding trials highlighted the possibility to reduce drastically the number of healthy volunteers and patients exposed to experimental drugs. This thesis furthermore addressed the benefits of OD in planning trials with bio analytical limits and toxicity constraints, through the development of novel optimality criteria that foremost pinpoint information and safety aspects. The use of these methodologies showed better estimation properties and robustness for the ensuing data analysis and reduced the number of patients exposed to severe toxicity by 7-fold.  Finally, predictive tools for maximum tolerated dose selection in Phase I oncology trials were explored for a combination therapy characterized by main dose-limiting hematological toxicity. In this example, Bayesian and model-based approaches provided the incentive to a paradigm change away from the traditional rule-based “3+3” design algorithm. Throughout this thesis several examples have shown the possibility of streamlining clinical trials with more model-based design and analysis supports. Ultimately, efficient use of the data can elevate the probability of a successful trial and increase paramount ethical conduct.

INTRODUÇÃO: Dengue é uma doença viral prevalente e potencialmente fatal associada à alteração da permeabilidade capilar e coagulopatia. Entretanto, não há estudos concernentes aos achados tromboelastométricos nesta doença. Realizamos o presente estudo para analisar pacientes com dengue e plaquetopenia por meio de um exame rápido, efetivo e a beira leito comparando com os exames convencionais de coagulação. MÉTODOS: Trata-se de um estudo observacional e transversal conduzido entre os dias 6 de abril a 5 de maio de 2015, em São Paulo, Brasil, durante epidemia de dengue. Foi realizado tromboelastometria ROTEM® em 53 pacientes com dengue e trombocitopenia em associação com exames convencionais de coagulação: tempo de protrombina (TP), international normalized ratio (INR), tempo de tromboplastina parcial ativado (TTPa), tempo de trombina (TT), contagem de plaquetas, fibrinogênio e d-dímero. Um grupo controle de pacientes foi estabelecido para comparação do status tromboelastométrico. RESULTADOS: Um total de 38 pacientes de 53 (71,7%) apresentaram anormalidades no INTEM e 29/53 (57,4%) no EXTEM. Em contrapartida, alterações no FIBTEM foram encontradas apenas em 3/53 (5,7%). Houve significância estatística em pacientes correlacionando alterações tromboelastométricas no EXTEM e INTEM e contagem de plaquetas (p=0,052) e (p=0,005), respectivamente; assim como os valores de fibrinogênio (p=0,006) e (p=0,021), respectivamente. O grupo controle (GC) apresentou status tromboelastométrico normal em 10/10 (100%) na análise do INTEM, EXTEM, FIBTEM. Avaliação do EXTEM demonstrou significância estatística entre o GC e o grupo Dengue: CT (p=0,044); CFT (p<0,001); MCF (p < 0,001) e Alpha (p < 0,001). Foram observados níveis normais de fibrinogênio (mediana: 290) e altos níveis de d-dímero (mediana: 1330) com IQR (800-1840). Todos os pacientes (53/53) apresentavam trombocitopenia abaixo de 100 x 109/L (mediana 77 x 109/L) IQR (63-88). Exames convencionais de coagulação revelaram-se completamente normais: TP (mediana: 100%) IQR (90-100); INR (mediana: 1,0) IQR (1,0-1,1); TTPa (mediana: 28,9 segundos) IQR (26,0-32,5) e TT (mediana: 18,2 segundos) IQR (17,0-19,5). Apenas (7/49) 14,3% pacientes apresentaram sangramento e (3/52) 5,8% necessitou de hospitalização. Não houve associação entre alterações tromboelastométricas com sangramento ou hospitalização. CONCLUSÕES: Dengue representa um processo inflamatório intenso, mantendo níveis normais de fibrinogênio. Portanto, FIBTEM mantém-se normal promovendo boa formação do coágulo sem risco imediato de sangramento. Não houve correlação entre os achados tromboelastométricos com os exames convencionais de coagulação, sugerindo que testes viscoelásticos são exames mais sensíveis para análise de coagulopatia precoce nessa população / INTRODUCTION: Dengue is a prevalent and potentially fatal viral disease associated with plasma leakage and coagulopathy, though no information is available on thromboelastometric profile. We performed this study to analyze dengue fever patients with thrombocytopenia clot changes through point-ofcare thromboelastometry tests and standard coagulation tests. METHODS: This was an observational, transversal and cross sectional study conducted between April 6th and May 5th 2015 in São Paulo, Brazil, during a dengue outbreak. Thromboelastometry ROTEM® was performed in 53 patients with dengue and thrombocytopenia, in association with conventional coagulation tests: prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time (TT); platelet count, fibrinogen level, and d-dimer. A control group of 10 patients was established to compare thromboelastometry profiles. RESULTS: A total of 38 patients in 53 (71,7%) had abnormalities in INTEM, 29 in 53 (57,4%) in EXTEM. Conversely, FIBTEM was abnormal in 3/53 (5,7%). Statistical analysis revealed significant relation in those patients with impairment EXTEM and INTEM with lowered platelet (p=0,052) and (p=0,005) respectively and lowered fibrinogen levels (p=0,006) and (p=0,021) respectively. Control group (CG) had normal status in 10/10 (100%) of INTEM, EXTEM, FIBTEM analysis. EXTEM analysis demonstrated statistical differences between CG and dengue group: CT (p=0,044); CFT (p < 0,001); MCF (p < 0,001) and Alpha (p < 0,001). Normal levels of fibrinogen (median: 290) and high levels of ddimer (median: 1330) IQR (800-1840) were found. All patients (53/53) had platelet under 100 x 109/L (median 77 x 109/L) IQR (63-88). Standard coagulation tests were completely normal: PT (median: 100%) IQR (90-100); INR (median: 1,0) IQR (1,0-1,1); aPTT (median: 28,9 seconds) IQR (26.0- 32,5) and TT (median: 18,2 seconds) IQR (17,0-19.5). Only (7/49) 14,3% patients had bleeding manifestations and (3/52) 5,8% needed hospitalization. There was no association between altered thromboelastometry with bleeding manifestations or hospitalization. CONCLUSIONS: Dengue represents an intense inflammatory process, maintaining normal levels of fibrinogen. FIBTEM remains normal providing good clot strength without immediate bleeding risk. There were no correlation between thromboelastometry findings and standard coagulation exams, suggesting that viscoelastic tests are more sensible method to analyze early coagulation impairments in this population

Pacientes envenenados pela serpente Bothrops jararaca manifestam uma tendência hemorrágica em que a plaquetopenia é um achado consistente. Manifestações clínicas sistêmicas, como sangramento de mucosas e microangiopatia trombótica em alguns pacientes, apresentam similaridades com sinais clínicos de doença de von Willebrand e púrpura trombocitopênica trombótica. Algumas proteínas do veneno - como a botrocetina (uma proteína relacionada às lectinas do tipo C) e as metaloproteinases do veneno (SVMP) - interferem direta ou indiretamente na interação entre plaquetas e o fator de von Willebrand (vWF) in vitro e in vivo. E dessa forma, podem contribuir para os sangramentos induzidos pelo envenenamento devido à importância que o vWF tem para a hemostasia primária. Pensando em compreender a participação do vWF do organismo e a botrocetina e as SVMP do veneno bruto de B. jararaca (BjV) na plaquetopenia induzida pelo envenenamento, utilizamos dois modelos experimentais: ratos Wistar heterogênicos e camundongos nocautes do gene Vwf (Vwf-/-). No modelo em ratos, o BjV foi pré-incubado com salina (controle positivo), um inibidor de metaloproteinases (Na2-EDTA), anticorpos policlonais anti-botrocetina, glicerol (veículo dos anticorpos), ou a combinação do Na2-EDTA e anticorpos anti-botrocetina; o grupo controle negativo foi injetado somente com salina. Após a administração subcutânea (s.c.) dos venenos tratados (1,6 mg/kg), amostras de sangue foram coletadas após 3, 6 ou 24 h, e analisaram-se a contagem de plaquetas, quantificação antigênica (vWF:Ag) e da atividade de ligação do vWF ao colágeno (vWF:CB), a atividade de ADAMTS13, a distribuição multimérica de vWF, e a atividade coagulante de fator VIII (FVIII). Para explorar a participação do vWF na plaquetopenia, camundongos nocautes de vWF (Vwf-/-) e camundongos controles (C57BL/6) foram injetados s.c. com BjV incubado com salina (grupo positivo do envenenamento) ou apenas salina (grupo controle negativo). As injeções dos tratamentos, bem como os períodos analisados foram idênticos aos dos ratos. Em nossos resultados, todos os ratos injetados com algum tratamento de BjV, inclusive nos animais que receberam veneno pré-tratado com anticorpo anti-botrocetina e/ou Na2-EDTA, apresentaram plaquetopenia, com maior intensidade em 6 h. Na avaliação do vWF foi encontrada uma grande variação individual nos grupos de tratamentos, porém ainda assim houve uma tendência a redução nos níveis de vWF:Ag em 3 e 6 h nos ratos que receberam BjV sem inibidores. A administração de BjV tratado somente com anticorpo anti-botrocetina promoveu uma maior redução nos níveis de vWF:Ag em 3 h, com retorno aos níveis semelhantes aos de controle negativo em 6 h e 24 h. A inibição sozinha das metaloproteinases não promoveu efeito importante, porém em 6 h, potencializou a ação do anticorpo anti-botrocetina na inibição conjunta do decréscimo de vWF:Ag e vWF:CB. A análise dos multímeros do vWF mostrou perfis bastante variáveis individualmente, porém os multímeros de alto peso molecular e intermediário tenderam a diminuir e os de baixo peso a aumentar nos animais que receberam algum tratamento com BjV, especialmente em 24 h. Na dosagem de FVIII, houve redução em 3 e 6 h em todos os ratos que receberam qualquer tratamento de BjV, sem grandes variações entre esses grupos. A atividade de ADAMTS13 apresentou uma redução dos valores em 3 e 6 h, que foi revertida pela inibição das metaloproteinases do veneno. Já nos camundongos, a plaquetopenia esteve presente em todos os animais nocautes e controles que receberam BjV, mostrando ser independente da presença de vWF. Nos camundongos controles (C57BL/6), não houve alterações evidentes em vWF:Ag durante o envenenamento, porém em 3 h houve uma tendência a sua diminuição. Em conjunto, nossos resultados mostram que a presença da botrocetina no veneno bruto não afeta a plaquetopenia desencadeada pelo envenenamento, porém influencia o vWF plasmático quantitativa e funcionalmente. As metaloproteinases do veneno têm forte efeito sobre a enzima fisiológica reguladora da atividade biológica do vWF, a ADAMTS13, que indiretamente pode afetar os níveis de vWF. Ademais, a intensidade da plaquetopenia durante o envenenamento de B. jararaca não depende da presença de vWF, e tendo em conta o caráter multifatorial do consumo plaquetário durante o envenenamento, sugerimos que outros mecanismos possam ser responsáveis pela plaquetopenia induzida pelo BjV. Com isso, concluímos que o consumo de vWF no envenenamento por B. jararaca é um fator contribuinte, porém não determinante, para as alterações da contagem plaquetária / Patients bitten by Bothrops snakes manifest a bleeding tendency in which thrombocytopenia is consistently observed. Systemic clinical manifestations, such as mucous bleeding and thrombotic microangiopathy in some patients, share similarities with symptoms of von Willebrand disease and thrombotic thrombocytopenic purpura. Some venom proteins - e.g. botrocetin (a C-type lectin-related protein) and snake venom metalloproteinases (SVMP) - disturbs, direct or indirectly, the interaction between platelets and von Willebrand factor (vWF) in vitro and in vivo, and may contribute thereby to snakebite-induced bleedings, once vWF is required for primary hemostasis. To better understand the relation between plasma vWF, and botrocetin and SVMPs from B. jararaca crude venom (BjV) in the thrombocytopenia induced by envenomation, we used two experimental models: Wistar heterogenic rats and vWF knockout mice (Vwf-/-). In the rat model, BjV was pre-incubated with saline (positive control), metalloproteinase inhibitor (Na2-EDTA), polyclonal anti-botrocetin antibodies, glycerol (antibody vehicle), or the combination of Na2-EDTA and anti-botrocetin antibodies; the negative control group was injected with saline only. After subcutaneous injection (s.c.) of treated venom (1.6 mg/kg), blood samples were collected after 3, 6 or 24 h, and platelet count, vWF antigen (vWF:Ag) and collagenbinding activity (vWF:CB), ADAMTS13 activity, vWF multimer distribution, and factor VIII (FVIII) coagulant activity were analyzed. To investigate the participation of vWF in thrombocytopenia, vWF knockout mice (Vwf-/-) and control mice (C57BL/6) were injected s.c. with saline only (negative control group) or BjV pre-incubated with saline (positive control group). The same protocols used for rats were accomplished in mice. Our results showed that all rats injected with any BjV treatment, including animals which received anti-botrocetin antibodies and/or Na2-EDTA-treated BjV, showed thrombocytopenia, with the nadir at 6h. vWF analysis exhibited a large individual variation among treatment groups, but there was a tendency to reduce vWF:Ag levels at 3 and 6 h in rats that received BjV pre-incubated with saline (without any inhibitor). Administration of BjV pre-incubated only with anti-botrocetin antibodies evoked a large reduction in vWF:Ag levels at 3 h, which returned to levels similar to those of the negative control group at 6 and 24 h. SVMP inhibition alone did not induce an important effect, but potentialized the activity of anti-botrocetin antibodies to inhibit the fall in both vWF:Ag and vWF:CB levels at 6 h. VWF multimer analysis had a large individual profile variation, although animals that received any BjV treatment tended to decrease the high and intermediate molecular weight multimers and to increase the low ones, especially at 24 h. FVIII showed diminished levels in all rats that received any BjV treatment at 3 and 6 h, without important variations among groups. Decreased levels of ADAMTS13 activity were noticed at 3 and 6 h, which were reverted by SVMP inhibition. In mice, thrombocytopenia was present in all control and knockout mice that received BjV, demonstrating independence of vWF presence. In control mice (C57BL/6), there were no relevant alterations in vWF:Ag during envenomation, although at 3 h there was a tendency to decrease it. Al together, our results showed that botrocetin present in crude venom does not affect thrombocytopenia induced by envenomation, but it changes the levels and function of plasma vWF. SVMP had a marked effect in ADAMTS13, the physiological enzyme that regulates vWF biological activity, which may affect vWF levels indirectly. In addition, thrombocytopenia during B. jararaca envenomation is independent of vWF, and considering the multifactorial features of platelet consumption during envenomation, we suggest that other mechanisms might account for BjV-induced thrombocytopenia. Therefore, we conclude that vWF consumption during B. jararaca envenomation is an ancillary mechanism, but not the main one to decrease platelet counts