Keshava S, Sundaram J, Rajulapati A, Pendurthi U R, Rao L V M
Department of Cellular and Molecular Biology, The University of Texas Health Science Center at Tyler, Tyler, TX, USA.
J Thromb Haemost. 2016 Mar;14(3):546-50. doi: 10.1111/jth.13244. Epub 2016 Feb 15.
ESSENTIALS: The role of tissue factor (TF) in recombinant factor VIIa (rFVIIa) therapy in hemophilia is unclear. An acquired mouse hemophilia model with very low or normal levels of human TF was used in the study. rFVIIa is equally effective in correcting the bleeding in mice expressing low or normal levels of TF. Pharmacological doses of rFVIIa restore hemostasis in hemophilia independent of TF.
Recombinant factor VIIa (rFVIIa) has been used widely for treating hemophilia patients with inhibitory autoantibodies against factor VIII or IX. Its mechanism of action is not entirely known. A majority of in vitro studies suggested that pharmacological concentrations of rFVIIa restore hemostasis in hemophilia in a phospholipid-dependent manner, independent of tissue factor (TF). However, a few studies suggested that a TF-dependent mechanism has a primary role in correction of bleeding by rFVIIa in hemophilia patients. Here, we investigated the potential contribution of TF in rFVIIa-induced hemostasis in hemophilia employing a model system of FVIII antibody-induced hemophilia in TF transgenic mice.
Mice expressing low levels of human TF (LTF mice), mice expressing relatively high levels of human TF (HTF mice) and wild-type mice (WT mice) had neutralizing anti-FVIII antibodies administered in order to induce hemophilia in these mice. The mice were then treated with varying concentrations of rFVIIa. rFVIIa-induced hemostasis was evaluated with the saphenous vein bleeding model.
Administration of FVIII inhibitory antibodies induced the hemophilic bleeding phenotype in all three genotypes. rFVIIa administration rescued the bleeding phenotype in all three genotypes. No significant differences were observed in rFVIIa-induced correction of bleeding between LTF and HTF mice that had FVIII antibodies administered.
Our results provide strong evidence supporting the suggestion that the hemostatic effect of pharmacological doses of rFVIIa stems from a TF-independent mechanism.
要点：组织因子（TF）在重组凝血因子VIIa（rFVIIa）治疗血友病中的作用尚不清楚。本研究使用了人TF水平极低或正常的获得性小鼠血友病模型。rFVIIa在纠正TF表达水平低或正常的小鼠出血方面同样有效。药理学剂量的rFVIIa可恢复血友病患者的止血功能，且与TF无关。
重组凝血因子VIIa（rFVIIa）已广泛用于治疗对凝血因子VIII或IX具有抑制性自身抗体的血友病患者。其作用机制尚不完全清楚。大多数体外研究表明，药理学浓度的rFVIIa以磷脂依赖性方式恢复血友病患者的止血功能，与组织因子（TF）无关。然而，一些研究表明，TF依赖性机制在rFVIIa纠正血友病患者出血中起主要作用。在此，我们采用TF转基因小鼠中FVIII抗体诱导的血友病模型系统，研究了TF在rFVIIa诱导的血友病止血中的潜在作用。
向表达低水平人TF的小鼠（LTF小鼠）、表达相对高水平人TF的小鼠（HTF小鼠）和野生型小鼠（WT小鼠）注射中和性抗FVIII抗体，以诱导这些小鼠患血友病。然后用不同浓度的rFVIIa治疗这些小鼠。用隐静脉出血模型评估rFVIIa诱导的止血情况。
给予FVIII抑制性抗体在所有三种基因型中均诱导出血友病出血表型。给予rFVIIa挽救了所有三种基因型的出血表型。在给予FVIII抗体的LTF和HTF小鼠之间，rFVIIa诱导的出血纠正方面未观察到显著差异。
我们的结果提供了有力证据，支持药理学剂量的rFVIIa的止血作用源于TF非依赖性机制这一观点。
