Tranexamic Acid Reduces Large Traumatic Bleeding and Mortality in Murine Iron Deficiency Anemia By Mechanisms Beyond Control of Fibrinolysis

Introduction

Iron deficiency anemia (IDA) is common. Some clinical evidence suggests that IDA may aggravate traumatic hemorrhage and compromise outcomes.

To study if IDA influences traumatic hemorrhage, coagulopathy, and mortality we developed a model of traumatic liver injury with and without tranexamic acid (TXA) in mice with dietary IDA and compared the results to control mice and mice after parenteral iron rescue.

Materials and Methods

Severe IDA was generated in C57BL/6J mice by starting an iron-deficient diet in 3-week-old mice for 8 weeks (+/- 1 mg intraperitoneal iron dextran 2 weeks before trauma). Control mice were fed a normal laboratory diet. IDA was confirmed by complete blood count, red cell indices, and liver iron. Mice (≈20 per group) were pre-treated with saline or TXA (10mg/kg) and subjected to liver laceration. Blood loss (weighing blood-soaked sponges from the abdomen), coagulopathy [APTT, Factor (F)II, FV, FVIII, FX, and fibrinogen), thrombin-antithrombin (TAT) and plasmin-antiplasmin (PAP) complexes] were analyzed at 60 minutes after trauma Cytokine levels (IL-1α, IL-1β, IL-2, IL-6, IL-10, MCP-1, RANTES, and TNFα) were measured at baseline, 60 minutes and 6 hours post-trauma. Data were expressed as median and compared by Mann-Whitney test. Seven-day survival was analyzed using Kaplan-Meier curves.

Results

IDA manifested as hypochromic/microcytic anemia with significantly lower hematocrits compared to normal controls (32% vs 48%, p=<0.0001) and hepatic iron content (20.04 µg/g vs. 72.41 µg/g, p=<0.0001), respectively. Parenteral iron repletion corrected anemia and hepatic iron stores (“iron replete” mice).

IDA mice experienced significantly higher blood loss compared to control mice (24.5 vs. 20.6 µL/g p=<0.0001), and TXA prophylaxis reduced blood loss significantly in both groups to ~15 µL/g. Blood loss in iron replete mice was 15.8 µL/g, and TXA did not reduce bleeding beyond the ~15 µL/g threshold. Bleeding led to a similar degree of acute traumatic coagulopathy (ATC) in all groups, characterized by APTT prolongation, TAT-complex formation, and depletion of FV, FVIII, and fibrinogen. FII and FX were not affected, consistent with the presence of ATC, rather than disseminated intravascular coagulation. TXA promoted the correction of ATC by near-normalization of TAT-complexes, FV, FVIII, and fibrinogen in all groups. In contrast, the extent of fibrinolysis differed in that PAP complex formation was significantly higher in IDA mice compared to control mice (44 vs 28 ng/mL, p=0.0004). TXA corrected PAP-complex formation and APTT only in control mice, without affecting these parameters in IDA mice. Seven-day survival was high in control and iron replete mice (~75%) without additional improvement by TXA. However, 7-day survival was lower in IDA mice (50%) and rescued by TXA (80%, p=0.04). A post-traumatic cytokine response was observed for the pro-inflammatory cytokines IL-1α, IL-6, MCP-1, RANTES, and TNFα. TXA mitigated this response substantially, but mostly in IDA mice, with little effect in control and iron replete mice.

Conclusion

IDA resulted in enhanced bleeding and mortality, which was rescued by parenteral iron correction or TXA prophylaxis. Interestingly, exaggerated fibrinolysis provoked by IDA could not be corrected by TXA, while TXA suppressed the pro-inflammatory cytokine response. This suggests that bleed and mortality rescue in IDA were less dependent on the anti-fibrinolytic effects of TXA, and more dependent on anti-inflammatory effects, which are poorly understood. These observations open new avenues to study pharmacodynamic effects of TXA beyond fibrinolysis inhibition, which may be particularly impactful for trauma rescue in the setting of anemia.