Reversal of the anticoagulant and anti-hemostatic effect of low molecular weight heparin by direct prothrombin activation

Lopap, found in the bristles of Lonomia obliqua caterpillar, is the first exogenous prothrombin activator that shows serine protease-like activity, independent of prothrombinase components and unique lipocalin reported to interfere with hemostasis mechanisms. To assess the action of an exogenous prothrombin activator reversing the anticoagulant and antihemostatic effect induced by low molecular weight heparin (LMWH), male New Zealand rabbits (N = 20, weighing 3.8-4.0 kg) allocated to 4 groups were anticoagulated with 1800 IU/kg LMWH (iv) over 2 min, followed by iv administration of saline (SG) or recombinant Lopap (rLopap) at 1 µg/kg (LG1) or 10 µg/kg (LG10), 10 min after the injection of LMWH, in a blind manner. Control animals (CG) were treated only with saline. The action of rLopap was assessed in terms of activated partial thromboplastin time (aPTT), prothrombin fragment F1+2, fibrinogen, and ear puncture bleeding time (BT) at 5, 10, 15, 17, 20, 30, 40, 60, and 90 min after initiation of LMWH infusion. LG10 animals showed a decrease of aPTT in more than 50% and BT near to normal baseline. The level of prothrombin fragment F1+2 measured by ELISA had a 6-fold increase with rLopap treatment (10 µg/kg) and was inversely proportional to BT in LMWH-treated animals. Thus, Lopap, obtained in recombinant form using E. coli expression system, was useful in antagonizing the effect of LMWH through direct prothrombin activation, which can be a possible strategy for the reversal of bleeding and anticoagulant events.

Antithrombotic effect of Lonomia obliqua caterpillar bristle extract on experimental venous thrombosis

The venom of Lonomia obliqua caterpillar may induce a hemorrhagic syndrome in humans, and blood incoagulability by afibrinogenemia when intravenously injected in laboratory animals. The possible antithrombotic and thrombolytic activities of L. obliqua caterpillar bristle extract (LOCBE) were evaluated in this study. The minimal intravenous dose of the extract necessary to induce afibrinogenemia and anticoagulation was 3.0 and 10.0 æg protein/kg body weight for rabbits and rats, respectively. In rabbits, this dose induced total blood incoagulability for at least 10 h and did not reduce the weight of preformed venous thrombi, in contrast to streptokinase (30,000 IU/kg). In rats, pretreatment with 5.0 and 10.0 æg/kg LOCBE prevented the formation of thrombi induced by venous stasis or by injury to the venous endothelium. The dose of 5.0 æg/kg LOCBE did not modify blood coagulation assay parameters but increased bleeding time and decreased plasma factor XIII concentration. When the extract was administered to rats at the dose of 10.0 æg/kg, the blood was totally incoagulable for 6 h. These data show that LOCBE was effective in preventing experimental venous thrombosis in rats, justifying further studies using purified fractions of the extract to clarify the mechanisms of this effect

Ausência de ação antitrombótica em trombose venosa experimental / Absence of antithrombotic effect of metronidazolin experimental venous thrombosis

Com base na utilização empírica do metronidazol no tratamento de picada de cobra e em uma possível ação fibrinolítica, alguns médicos brasileiros o usaram no tratamento de trombose venosa profunda, embora não existam estudos que justifiquem tal emprego. OBJETIVO: Verificar possível existência de efeito antitrombótico do metronidazol em modelo de trombose induzida na veia cava de ratos e uma eventual ação anticoagulante ou fibrinolítica dessa droga. MÉTODO: 71 ratos da raça Wistar foram usados em 4 experimentos. No primeiro, 29 animais foram divididos em três grupos: controle (solução salina), heparina (200UI/kg) e metronidazol (6mg/kg). 10 minutos após a injeção IV a trombose foi induzida pela ligadura da veia cava, distalmente à veia renal esquerda. Três horas depois, a veia cava era removida e aberta, e o trombo, se presente, retirado para pesagem, sendo o sangue do animal retirado para medida do TTPA, TT e TP. No segundo experimento, o sangue foi retirado dos animais (n=18) 10 minutos após a injeção das drogas, para medida dos mesmos parâmetros. No terceiro experimento os animais (n=22) foram injetados com metronidazol ou salina e o tempo de lise de euglobulina medido 3 horas após. No quarto experimento, 22 animais foram sorteados para um de dois grupos: controle, com injeção IV de 12ml de salina ou metronidazol, (12mg/kg), sendo a trombose induzida 10 minutos após. RESULTADOS: Não houve diferença entre os grupos controles e os grupod tratados com metronidazol, em relação à incidência e peso dos trombos e com relação aos parâmetros hemostáticos estudados. Nos animais tratados com heparina não houve formção de trombos, havendo aumento de TTPA e de TT aos 10 minutos, e de TT, após 3 horas. CONCLUSÄO: No modelo experimental empregado, o metronidazol não mostrou efeito antitrombótico e também ação sobre o parâmetros hemostáticos estudados, sugerindo que o uso clínico dessa droga no tratamento de trombose venosa é duvidoso, a menos que outros estudos venham demosntrar algum efeito benéfico.

Platelet activation following application of an esmarch bandage and tourniquet in rabbits

The present study evaluates platelet activation following application of an Esmarch bandage and a tourniquet, procedures commonly employed to provide a bloodless operative field during limb surgery. Platelet aggregation was increased in blood samples taken from rabbits 60 min after an Esmarch bandage was applied to one thigh and immediately released. When this treatment was combined with the application of a tourniquet for 60 min, a procedure which alone did not affect platelet aggregation, results were similar to those obtained following the Esmarch bandage alone. These data suggest that tissue compression produced by application of an Esmarch bandage, but not the ischemia derived from the tourniquet, produced platelet aggregation

Comparative study of the action of topical heparinoids on the evolution of experimental thrombophlebitis

The action of threem different topical heparinoids on the evolution of experimental thrombophlebitis was studies. Thrombophlebitis was induced in the marginal vein of the ear of rabbits by stasis and inection of hypertonic glucose solution. Forty-eight hours later animals were allocated to three treatment groups and a control group. The substances were applied over the affected vein three times a day for 6 days and the ears inspected daily by transillumination. After 7 days, the animals were killed and anatomopathological studies performed. No difference in thrombus frequency or inflamatory reaction was observed between the animals treated with heparinoids and the control group, or among the treated groups