Mitigation of Vascular Permeability Using Bradykinin Receptor Antagonist and Anti-Fibrinolytic Agent in Rats with Polytrauma and Hemorrhagic Shock

Introduction: Clinical studies suggest that one third of patients suffering major trauma develop acute traumatic coagulopathy (ATC), which is associated with increased morbidity and mortality. Recent evidence in both animal and clinical studies has shown that development of ATC is associated with an increase in fibrinolytic activity, initiated by an elevation in tissue plasminogen activator (tPA) immediately after trauma. Previous studies demonstrate that administration of the anti-fibrinolytic agent tranexamic acid (TXA) not only inhibits fibrinolytic activity in traumatized tissue but also attenuates lung edema after resuscitation in rats with polytrauma and hemorrhagic shock, suggesting a potential correlation between fibrinolysis and vascular permeability. One of the underlying mechanisms of acute elevation in vascular permeability after severe trauma is associated with an elevation of bradykinin activity due to activation of the tPA-plasmin-bradykinin pathway. This study will test the hypothesis that early intervention by administration of a bradykinin receptor antagonist with or without TXA prior to resuscitation attenuates edema in the tissues after resuscitation in rats with polytrauma/hemorrhagic shock.

Method: Sprague-Dawley rats (350-450g) under anesthesia with isoflurane received polytrauma followed by hemorrhage (40% of blood volume). The rats either received vehicle (normal saline) or bradykinin receptor-2 antagonist (BR-2A (HOE140, 0.5mg/kg)), TXA (20mg/kg) or BR-2A/TXA via femoral vein at 45min after trauma (n=6-8/each group), followed by resuscitation with Lactated Ringer's solution (20% of blood volume) at 60min after trauma. Four normal rats, not undergoing surgical procedures were treated as normal control. At 2hr after trauma (1hr after resuscitation), the rats were euthanized and the tissues from internal organs were harvested and weighed for wet weight. The tissue samples were then transferred to a 60⁰C oven for 10-14 days. The dry weight was determined when the weight of dried tissue was constant for three consecutive days. The wet-dry weight ratio was then calculated to represent the water content for each tissue. The wet-dry weight ratio was also measured in traumatized tissues collected from the injured sites of liver, intestine and skeletal muscle (at hindlimb). At 2hr after trauma, prothrombin time (PT) was measured for systemic hemostatic condition, and the resuscitation outcome was assessed by lactate levels.

Results: The wet/dry weight ratio is different in organs due to underlying structure and water content. Trauma, hemorrhage and resuscitation led to a significant elevation of wet/dry weight ratio in a majority of the organs (except for heart, kidney, and stomach). The wet/dry weight ratio was significantly higher in traumatized tissues than non-traumatized tissues (at liver, intestine and skeletal muscle). BR-2A significantly decreased the wet/dry weight ratio of the brain (4.51±0.03 (BR-2A) vs 4.64±0.03 (Vehicle)), but had no effect on the other organs. TXA significantly reduces the wet/dry weight ratio of the lung and intestine (lung: 5.02±0.07 (BR-2A) vs 5.23±0.06 (Vehicle), p=0.003; Intestine: 4.16±0.10 (BR-2A) vs 4.45±0.07 (Vehicle), p=0.036) but not in the brain and other tissues. The combination of BR-2A with TXA significantly decreased elevation of wet/dry weight ratio of the brain, lung and intestine, but there was no synergistic effect on wet/dry weight ratio found in any organs. However, the rats treated with combination treatment of BR-2A and TXA had the lowest lactate level at 2hr after trauma as compared to rats treated with vehicle (1.85±0.15 vs 3.39±0.29 mmol/l, p=0.032) suggesting an overall improvement of resuscitation outcome. BR-2A, TXA or a combination of the two did not cause significant change in MAP and HR, and had no significant effect on systemic coagulopathy (elevation of prothrombin time) at 2hr after trauma and hemorrhage.

Conclusions: This study suggests that BR-2A and TXA independently mitigate tissue-specific vascular permeability in trauma and hemorrhagic shock. Future studies are necessary to investigate the optimal dose and timing of administration of BR-2A or BR-2A with TXA in trauma and hemorrhagic shock to improve the outcome and efficacy of treatment.