Hibernation and Thrombo-protection: Exploring Fibrinolytic Mechansims in the Ametrican Black Bear

Abstract

Research Question: Are there differences in fibrinolytic regulatory mechanisms in naturally hibernating American black bears (Ursus americanus) that may serve as a basis for ¿thromboprotection¿ from stasis? Specifically, how do tissue plasminogen, urokinase plasminogen activator, and plasminogen activator inhibitor-1 expression patterns differ in hibernating vs active bears?

Background and Significance: Thrombotic complications are a common pathology following days of stagnation, periods of immobility, and hospital admissions. The commonality of thrombotic events is lethal and contributes to one in four deaths worldwide. Although deep vein thrombosis (DVT) cases reduced from 264 per 100,000 to 167 per 100,000 from 1999 to 2010, researching control and therapeutic measures continue to expand our understanding. Rudolf Virchow in 1847 published a triad of factors describing stasis, a period of inactivity, as a contributing factor to venous thrombosis. Yet, hibernating animals, and bears in particular, are dormant and inactive for three to four months with minimal thrombotic complications. These mammals provide an opportunity to expand our scientific knowledge of fibrinolysis mechanisms in relationship to stasis from Virchow¿s Triad.

Materials and Methods: This cross-translational study will entail recruitment of hibernating and non-hibernating American black bears (Ursus americanus). Hibernation was determined by level of inactivity and monitoring of body temperature with specific parameters determined. We have a professional working relationship with the Michigan Department of Natural Resources; a state agency with ongoing Ursus americanus research. After IUACA and animal husbandry approval at the Michigan resource, and per their established methods, blood draws were completed under anesthesia via the femoral or jugular veins following strict protocols demonstrated by Friedrich et al. during active summertime and hibernation. Samples were frozen to -80 degrees to maintain consistency of factors. Cell count, hemostasis testing, and clotting factor assays are to be performed at Baylor All Saints pathology laboratory in Fort Worth, Texas.

Results: Previous studies conducted by Friedrich et al. demonstrated marked reductions in Factor XI, Factor XII, vWF, a prolonged PT and aPTT, and an increase in antithrombin in blood samples from hibernating bears, and we attempted to confirm these findings. We hypothesize that urokinase and tissue plasminogen activator levels will be increased to enhance fibrinolysis to maintain coagulation homeostasis. In partnership with the Michigan Department of Natural Resources, we collected 16 live bear samples during the winter and spring of 2023. Our samples have been successful stored at negative 80-degrees Fahrenheit and await delivery to Baylor All Saints in Fort Worth, Texas. We have sufficient sample collection to run appropriate assays and adequate data to test our hypothesis in spring of 2024.

Conclusion: Our study has opened the door to further explore cross-translational opportunities. American black bears have enabled us to see further than human studies and understand the interrelatedness that is visible in everyday life. We look forward to processing of 16 samples of bear specimens, and irrespective of the results, we have demonstrated through execution of this project that we could execute a meaningful multi-institutional collaboration delivering samples for scientific analysis of which there are only two other global examples. I have learned how to effectively establish partnerships to complete seemingly impossible work and know this will impact my career as a clinician and professional.