Mann BioConsulting, Gaithersburg, MD, USA.
Department of Medicine, Mount Auburn Hospital, Cambridge, MA, USA.
Haemophilia. 2021 May;27(3):332-339. doi: 10.1111/hae.14300. Epub 2021 Mar 29.
The majority of clotting factor IX (FIX) resides extravascularly, in the subendothelial basement membrane, where it is important for haemostasis.
We summarize preclinical studies demonstrating extravascular FIX and its role in haemostasis and discuss clinical observations supporting this. We compare the in vivo binding of BeneFIX and the extended half-life FIX, Alprolix , to extravascular type IV collagen (Col4).
Three mouse models of haemophilia were used: the FIX knockout as the CRM model and two knock-in mice, representing a CRM model of a commonly occurring patient mutation (FIX ) or a mutation that binds poorly to Col4 (FIX ). The murine saphenous vein bleeding model was used to assess haemostatic competency. Clinical publications were reviewed for relevance to extravascular FIX.
CRM status affects recovery and prophylactic efficacy. Prophylactic protection decreases 5X faster in CRM animals. Extravascular haemostasis can explain unexpected breakthrough bleeding in patients treated with some EHL-FIX therapeutics. In mice, both Alprolix and BeneFIX bind Col4 with similar affinities (Kd20-40 nM) and show dose-dependent recoveries. As expected, the concentration of binding sites in the mouse calculated for Alprolix (574 nM) was greater than for BeneFIX (405 nM), due to Alprolix binding to both Col4 and the endothelial cell neonatal Fc receptor.
Preclinical and clinical results support the interpretation that FIX plays a role in haemostasis from its extravascular location. We believe that knowing the CRM status of haemophilia B patients is important for optimizing prophylactic dosing with less trial and error, thereby decreasing clinical morbidity.
大多数凝血因子 IX（FIX）位于血管外，在基底膜下的内皮细胞中，这对止血非常重要。
我们总结了表明血管外 FIX 及其在止血中的作用的临床前研究，并讨论了支持这一观点的临床观察。我们比较了 BeneFIX 和延长半衰期 FIX（Alprolix）与血管外 IV 型胶原（Col4）的体内结合。
使用了三种血友病小鼠模型：FIX 敲除作为 CRM 模型，以及两种基因敲入小鼠，代表了一种常见患者突变（FIX）或一种与 Col4 结合不良的突变（FIX）的 CRM 模型。使用小鼠隐静脉出血模型来评估止血能力。临床出版物被审查以确定与血管外 FIX 相关的内容。
CRM 状态会影响恢复和预防效果。CRM 动物的预防保护作用下降约 5 倍。血管外止血可以解释一些 EHL-FIX 治疗药物治疗的患者出现意外突破性出血的情况。在小鼠中，Alprolix 和 BeneFIX 与 Col4 的结合亲和力相似（Kd~20-40 nM），并显示出剂量依赖性的恢复。正如预期的那样，由于 Alprolix 与 Col4 和内皮细胞新生儿 Fc 受体结合，因此计算出的 Alprolix 在小鼠中的结合位点浓度（574 nM）高于 BeneFIX（405 nM）。
临床前和临床结果支持 FIX 从其血管外位置发挥止血作用的解释。我们认为，了解血友病 B 患者的 CRM 状态对于优化预防剂量非常重要，可以减少试验和错误，从而降低临床发病率。
