Sara R. Abrahams

Hemostatic immaturity in neonates presents critical challenges, especially during surgery, where bleeding and thrombosis risks are elevated. Current treatments rely on transfusing adult blood products, which may cause complications resulting from structural and functional differences between neonatal and adult fibrinogen. To address this, we developed hemostatic B-knob–triggered microgels (BK-TriGs) that target and bridge fibrinogen hole b sites. Functionalized with a fibrin hole b–specific peptide, BK-TriGs enhance clot density and resistance to degradation. In vitro studies using neonatal platelet-poor plasma (PPP) showed that at an optimal concentration, BK-TriGs increased clot density by more than 100% and improved stability by reducing fibrinolysis. Under flow conditions, BK-TriGs promoted robust clot formation compared to plasma-only controls. In an in vivo fib-null (Fga−/−) mouse model transfused with neonatal fibrinogen, BK-TriGs reduced blood loss by 50 to 60% and enhanced fibrin deposition at wound sites. This targeted approach offers a safer, more effective hemostatic solution tailored to neonatal clotting needs.

BACKGROUND: Obesity predisposes individuals to multiple pathologies, including metabolic dysfunction–associated steatotic liver disease and diabetes. Although it is known that accumulation of proinflammatory macrophages within adipose tissues drives adiposity and provokes obesity-linked sequelae, the molecular mechanisms that provoke macrophage dysfunction in obesity remain elusive. Macrophages express high levels of uPA (urokinase plasminogen activator), and uPA has been implicated in leukocyte migration. METHODS: Human adipose tissues from patients receiving bariatric surgery were collected and analyzed for uPA protein levels. To determine the impact of uPA in adipose tissue and subsequent high-fat diet (HFD)–induced weight gain and metabolic diseases, a novel mouse model with a conditional knockout of uPA ( Plau ^{fl /fl} ) was generated. Plau ^WT/WT , Plau ^KO/KO (global uPA deficiency), and Plau ^fl/fl /LysM Cre+ (conditional uPA deficiency in macrophages) mice were fed low-fat diet or HFD for up to 20 weeks. RESULTS: Protein levels of visceral adipose tissue uPA positively correlated with body mass index in patients with obesity, and uPA levels decreased in adipose tissue 2 years after bariatric surgery. The expression and activity of uPA also increased in the adipose tissue of HFD-fed control mice. Plau ^KO/KO mice displayed reduced weight gain and metabolic sequelae through 14 weeks on a HFD compared with Plau ^WT/WT mice, but not with prolonged HFD feeding. Interestingly, Plau ^fl/fl /LysM Cre+ mice developed HFD-induced metabolic pathologies equivalently to Plau ^WT/WT mice. CONCLUSIONS: Our findings suggest that global uPA deletion, but not selective deletion of uPA in LysM+ myeloid cells, attenuates the development of early-stage HFD-driven obesity and pathologies consistent with metabolic syndrome.

Antifibrinolytic drugs are used extensively for on-demand treatment of severe acute bleeding. Controlling fibrinolysis may also be an effective strategy to prevent or lessen chronic recurring bleeding in bleeding disorders such as hemophilia A (HA), but current antifibrinolytics have unfavorable pharmacokinetic profiles. Here, we developed a long-lasting antifibrinolytic using small interfering RNA (siRNA) targeting plasminogen packaged in clinically used lipid nanoparticles (LNPs) and tested it to determine whether reducing plasmin activity in animal models of HA could decrease bleeding frequency and severity. Treatment with the siRNA-carrying LNPs reduced circulating plasminogen and suppressed fibrinolysis in wild-type and HA mice and dogs. In HA mice, hemostatic efficacy depended on the injury model; plasminogen knockdown improved hemostasis after a saphenous vein injury but not tail vein transection injury, suggesting that saphenous vein injury is a murine bleeding model sensitive to the contribution of fibrinolysis. In dogs with HA, LNPs carrying siRNA targeting plasminogen were as effective at stabilizing clots as tranexamic acid, a clinical antifibrinolytic, and in a pilot study of two dogs with HA, the incidence of spontaneous or excess bleeding was reduced during 4 months of prolonged knockdown. Collectively, these data demonstrate that long-acting antifibrinolytic therapy can be achieved and that it provides hemostatic benefit in animal models of HA.