Tfpi, short for tissue factor pathway inhibitor, is a multivalent Kunitz-type serine protease inhibitor. It plays a crucial role in regulating tissue factor-induced coagulation via factor Xa-dependent feedback inhibition of the tissue factor-factor VIIa complex, thus down-regulating the initiation of coagulation [3,6,7]. This regulation occurs within the extrinsic blood coagulation pathway, which is essential for maintaining proper hemostasis in the body [1].

In the context of hemophilia, a severe bleeding disorder, inhibition of Tfpi has emerged as a potential treatment strategy. Multiple studies have explored this concept. For instance, several therapeutic agents that inhibit Tfpi are in development. Inhibiting Tfpi can restore functional hemostasis through the extrinsic blood coagulation pathway without requiring the activity of factors VIII or IX, which are missing in hemophilia patients [1,3]. Additionally, longitudinal observations in paediatric Haemophilia A patients have shown that Tfpi levels (both total Tfpi concentrations and Tfpi activity) tend to decrease over age during childhood, which is relevant for translating adult doses of Tfpi inhibitors to paediatric patients [4]. Also, protein S acts as a cofactor for Tfpi, facilitating optimal factor Xa-inhibition and efficient down-regulation of thrombin generation in plasma [2,5,8].

In conclusion, Tfpi is a key regulator in the extrinsic blood coagulation pathway. Model-based research, especially in the context of haemophilia, has shown that targeting Tfpi can potentially restore hemostasis. Understanding Tfpi's functions and its regulation by co-factors like protein S, along with the knowledge of its age-related changes in paediatric haemophilia patients, provides valuable insights for developing novel treatments for haemophilia [1,2,3,4,5,8].

References:

1. Peterson, Julie A, Maroney, Susan A, Mast, Alan E. . Targeting TFPI for hemophilia treatment. In Thrombosis research, 141 Suppl 2, S28-30. doi:10.1016/S0049-3848(16)30359-0. https://pubmed.ncbi.nlm.nih.gov/27207418/

2. Peraramelli, Sameera, Rosing, Jan, Hackeng, Tilman M. 2012. TFPI-dependent activities of protein S. In Thrombosis research, 129 Suppl 2, S23-6. doi:10.1016/j.thromres.2012.02.024. https://pubmed.ncbi.nlm.nih.gov/22425215/

3. Chowdary, Pratima. 2018. Anti-tissue factor pathway inhibitor (TFPI) therapy: a novel approach to the treatment of haemophilia. In International journal of hematology, 111, 42-50. doi:10.1007/s12185-018-2548-6. https://pubmed.ncbi.nlm.nih.gov/30302740/

4. Schwers, Stephan, Shah, Anita, Linardi, Camila, Zhang, Yang, Willmann, Stefan. 2023. Longitudinal observations of TFPI levels in paediatric Haemophilia A patients. In Haemophilia : the official journal of the World Federation of Hemophilia, 29, 1142-1149. doi:10.1111/hae.14813. https://pubmed.ncbi.nlm.nih.gov/37335569/

5. Hackeng, T M, Maurissen, L F A, Castoldi, E, Rosing, J. . Regulation of TFPI function by protein S. In Journal of thrombosis and haemostasis : JTH, 7 Suppl 1, 165-8. doi:10.1111/j.1538-7836.2009.03363.x. https://pubmed.ncbi.nlm.nih.gov/19630792/

6. Osterud, Bjarne. 2011. Tissue factor/TFPI and blood cells. In Thrombosis research, 129, 274-8. doi:10.1016/j.thromres.2011.11.049. https://pubmed.ncbi.nlm.nih.gov/22197177/

7. Petersen, Lars C. 2012. Hemostatic properties of a TFPI antibody. In Thrombosis research, 129 Suppl 2, S44-5. doi:10.1016/j.thromres.2012.02.030. https://pubmed.ncbi.nlm.nih.gov/22405586/

8. Hackeng, Tilman M, Rosing, Jan. 2009. Protein S as cofactor for TFPI. In Arteriosclerosis, thrombosis, and vascular biology, 29, 2015-20. doi:10.1161/ATVBAHA.108.177436. https://pubmed.ncbi.nlm.nih.gov/19661488/