“COVID-19 Pandemic Perspectives:  A Scientific Silver Lining?”

Obesity is a prevalent prothrombotic risk factor marked by enhanced fibrin formation and suppressed fibrinolysis. Fibrin both promotes thrombotic events and drives obesity pathophysiology, but a lack of essential analytical tools has left fibrinolytic mechanisms affected by obesity poorly defined. Using a plasmin-specific fluorogenic substrate, we developed a plasmin generation (PG) assay for mouse plasma that is sensitive to tissue plasminogen activator, α₂-antiplasmin, active plasminogen activator inhibitor (PAI-1), and fibrin formation, but not fibrin crosslinking. Compared with plasmas from mice fed a control diet, plasmas from mice fed a high-fat diet (HFD) showed delayed PG and reduced PG velocity. Concurrent to impaired PG, HFD also enhanced thrombin generation (TG). The collective impact of abnormal TG and PG in HFD-fed mice produced normal fibrin formation kinetics but delayed fibrinolysis. Functional and proteomic analyses determined that delayed PG in HFD-fed mice was not due to altered levels of plasminogen, α₂-antiplasmin, or fibrinogen. Changes in PG were also not explained by elevated PAI-1 because active PAI-1 concentrations required to inhibit the PG assay were 100-fold higher than circulating concentrations in mice. HFD-fed mice had increased circulating thrombomodulin, and inhibiting thrombomodulin or thrombin-activatable fibrinolysis inhibitor (TAFI) normalized PG, revealing a thrombomodulin- and TAFI-dependent antifibrinolytic mechanism. Integrating kinetic parameters to calculate the metric of TG/PG ratio revealed a quantifiable net shift toward a prothrombotic phenotype in HFD-fed mice. Integrating TG and PG measurements may define a prothrombotic risk factor in diet-induced obesity.

Background: Hemophilia A results from the absence, deficiency or inhibition of factor VIII . Bleeding is treated with hemostatic agents (FVIII , recombinant activated FVII [rFVII a], anti‐inhibitor coagulation complex [FEIBA ], or recombinant porcine FVIII [rpFVIII ]). Despite treatment, some patients have prolonged bleeding. FXIII ‐A₂B₂ (FXIII ) is a protransglutaminase. During clot contraction, thrombin‐activated FXIII (FXIII a) crosslinks fibrin and α₂‐antiplasmin, which promotes red blood cell retention and increases clot stability and weight. We hypothesized that FXIII cotreatment in hemophilia would accelerate FXIII activation, leading to increased fibrin crosslinking. Methods: FVIII ‐deficient plasma and whole blood were clotted with or without hemostatic agents (FVIII , rFVII a, FEIBA , or recombinant B‐domain‐deleted porcine FVIII [rpFVIII ]) and/or FXIII . The effects on FXIII activation, thrombin generation, fibrin and α₂‐antiplasmin crosslinking, clot formation and clot weight were measured by western blotting, calibrated automated thrombography, thromboelastography, and clot contraction assays. Results: As compared with FVIII ‐treated hemophilic plasma, FVIII + FXIII cotreatment accelerated FXIII a formation without increasing thrombin generation. As compared with buffer‐treated or FXIII ‐treated hemophilic plasma, FVIII treatment and FVIII + FXIII cotreatment increased the generation and amount of crosslinked fibrin, including α‐chain‐rich high molecular weight species and crosslinked α₂‐a�Գپ��������������. In the presence of FVIII inhibitors, as compared with hemostatic treatments (rFVII a, FEIBA , or rpFVIII ) alone, FXIII cotreatment increased whole blood clot weight. Conclusion: In hemophilia A plasma and whole blood, FXIII cotreatment with hemostatic agents accelerated FXIII a formation, increased the generation and amount of fibrin α‐chain crosslinked species, accelerated α₂‐antiplasmin crosslinking, and increased clot weight. FXIII cotreatment with hemostatic therapy may augment hemostasis through increased crosslinking of fibrin and α₂‐a�Գپ��������������.