Revised model of the tissue factor pathway of thrombin generation: Role of the feedback activation of FXI.

BACKGROUND: Biochemical reaction networks are self-regulated in part due to feedback activation mechanisms. The tissue factor (TF) pathway of blood coagulation is a complex reaction network controlled by multiple feedback loops that coalesce around the serine protease thrombin. OBJECTIVES: Our goal was to evaluate the relative contribution of the feedback activation of coagulation factor XI (FXI) in TF-mediated thrombin generation using a comprehensive systems-based analysis. MATERIALS AND METHODS: We developed a systems biology model that improves the existing Hockin-Mann (HM) model through an integrative approach of mathematical modeling and in vitro experiments. Thrombin generation measured using in vitro assays revealed that the feedback activation of FXI contributes to the propagation of thrombin generation based on the initial concentrations of TF or activated coagulation factor X (FXa). We utilized experimental data to improve the robustness of the HM model to capture thrombin generation kinetics without a role for FXI before including the feedback activation of FXI by thrombin to construct the extended (ext.) HM model. RESULTS AND CONCLUSIONS: Using the ext.HM model, we predicted that the contribution of positive feedback of FXI activation by thrombin can be abolished by selectively eliminating the inhibitory function of tissue factor pathway inhibitor (TFPI), a serine protease inhibitor of FXa and TF-activated factor VII (FVIIa) complex. This prediction from the ext.HM model was experimentally validated using thrombin generation assays with function blocking antibodies against TFPI and plasmas depleted of FXI. Together, our results demonstrate the applications of combining experimental and modeling techniques in predicting complex biochemical reaction systems.

Fixed rehabilitation of patient with aggressive periodontitis using zygoma implants.

Treatment of patients with aggressive periodontitis has always been a challenge to the clinician. Both young and old are known to be affected by this progressive destructive condition of the supporting dental structures. Although dental implants have been offered as a viable treatment alternative for such patients, additional procedures (like bone grafting) and delayed protocols have limited their usage. This case report describes the treatment of a young patient with aggressive periodontitis using a graftless implant solution. Zygoma implants in conjunction with conventional implants were used with immediate loading.