A Novel Synthetic Short-Chain Polyphosphate (polyP) Complexed with Silica Nanoparticle (SNP) Improves Hemostatic Outcomes in Severe Swine and Rat Injury Models

Introduction: The majority of deaths from hemorrhage are thought to be preventable, as up to 90% are associated with non-compressible bleeding sites and/or delays to hemostatic control. A novel synthetic biomimetic of platelet polyP, complexed with silica nanoparticles (polyP-SNP complex), is under development as a pro-hemostatic therapeutic for serious or life-threatening bleeding. In vitro, the polyP-SNP complex was found to accelerate thrombin generation and improve kinetic clotting parameters as measured by thromboelastography (TEG). The polyP-SNP complex was designed to address the leading, predictable causes of preventable death. With systemic administration it reaches non-compressible bleeding sites, it can be rapidly administered, and it acts to accelerate clotting.

Aims: We assessed the capability of the polyP-SNP complex to improve bleeding outcomes after serious injury in two animal models (Grade V liver injury in swine; tail transection in rats).

Methods:

Swine: Sus scrofa pigs were anesthetized and subjected to splenectomy. After a 15-minute stabilization period, the animals were treated with the polyP-SNP complex (5 mg/kg or 7.5 mg/kg, total N = 5) or an equivalent volume of saline (control, N = 6) by IV injection over 5-7 minutes prior to a standardized Grade V liver injury. The liver injury was allowed to bleed freely for 30 seconds, after which pre-weighed laparotomy pads were applied to the injury and pressure was applied by hand for 3 minutes. Manual pressure was released and a suction catheter was placed in the anterior abdomen, which was then closed with towel clamps. As a result, bleeding time data was not collected. All animals were then monitored until they expired or for 1 hour at which time they were euthanized. Blood loss was measured using pre-weighed suction canisters and laparotomy pads. At the conclusion of the experiment, the abdomen was suctioned to remove free blood and blood clots, and laparotomy pads were weighed. Complete necropsy and histopathologic analyses were performed on major organs of all animals.

Rats: Anesthetized Sprague-Dawley rats were treated with the polyP-SNP complex 5 mg/kg (N = 9), 10 mg/kg (N = 7), or an equivalent volume of isotonic saline (control, N = 7) by IV injection over 5 minutes prior to tail amputation. Each rat’s tail was amputated at the 50% mark from the tail tip and the stump was placed in a pre-weighed Falcon tube containing 0.9% saline. The bleeding time was monitored, and blood loss was collected for 1 hour. Blood clots were quantitively assessed for mass and qualitatively described.

Results: In swine, the polyP-SNP complex reduced blood loss by 59% versus control (p<0.05). One control animal died post-injury, while all the polyP-SNP complex-treated animals survived to 1 hour. In rats, the polyP-SNP complex reduced bleeding time by 91% (p<0.0001) versus control. While control rats bled for nearly the entire duration of the study (56 ± 7.3 minutes), bleeding time in the polyP-SNP complex treated rats ceased by the 5-minute (± 0.9 minutes) mark. Mean blood loss was reduced by 33% (p<0.05) relative to control. Overall, there were no significant differences between the polyP-SNP complex doses with respect to hemostatic outcomes. Blood clots were smaller and denser (by touch) for the polyP-SNP complex-treated animals versus control. The average severity score of histopathology findings for the polyP-SNP complex was lower than that of control (0.6 versus 1.0, respectively; 0 to 3 scale).

Conclusions: The polyP-SNP complex administered IV significantly reduces bleeding time and blood loss in rats and pigs after standardized injury. The polyP-SNP complex has potential as a pro-hemostatic therapeutic for serious or life-threatening bleeding.