Trauma patients have reduced ex vivo flow-dependent platelet hemostatic capacity in a microfluidic model of vessel injury.

Trauma is the leading cause of death in individuals up to 45 years of age. Alterations in platelet function are a critical component of trauma-induced coagulopathy (TIC), yet these changes and the potential resulting dysfunction is incompletely understood. The lack of clinical assays available to explore platelet function in this patient population has hindered detailed understanding of the role of platelets in TIC. The objective of this study was to assess trauma patient ex vivo flow-dependent platelet hemostatic capacity in a microfluidic model. We hypothesized that trauma patients would have flow-regime dependent alterations in platelet function. Blood was collected from trauma patients with level I activations (N = 34) within 60 min of hospital arrival, as well as healthy volunteer controls (N = 10). Samples were perfused through a microfluidic model of injury at venous and arterial shear rates, and a subset of experiments were performed after incubation with fluorescent anti-CD41 to quantify platelets. Complete blood counts were performed as well as plasma-based assays to quantify coagulation times, fibrinogen, and von Willebrand factor (VWF). Exploratory correlation analyses were employed to identify relationships with microfluidic hemostatic parameters. Trauma patients had increased microfluidic bleeding times compared to healthy controls. While trauma patient samples were able to deposit a substantial amount of clot in the model injury site, the platelet contribution to microfluidic hemostasis was attenuated. Trauma patients had largely normal hematology and plasma-based coagulation times, yet had elevated D-Dimer and VWF. Venous microfluidic bleeding time negatively correlated with VWF, D-Dimer, and mean platelet volume (MPV), while arterial microfluidic bleeding time positively correlated with oxygenation. Arterial clot growth rate negatively correlated with red cell count, and positively with mean corpuscular volume (MCV). We observed changes in clot composition in trauma patient samples reflected by significantly diminished platelet contribution, which resulted in reduced hemostatic function in a microfluidic model of vessel injury. We observed a reduction in platelet clot contribution under both venous and arterial flow ex vivo in trauma patient samples. While our population was heterogenous and had relatively mild injury severity, microfluidic hemostatic parameters correlated with different patient-specific data depending on the flow setting, indicating potentially differential mechanistic pathways contributing to platelet hemostatic capacity in the context of TIC. These data were generated with the goal of identifying key features of platelet dysfunction in bleeding trauma patients under conditions of flow and to determine if these features correlate with clinically available metrics, thus providing preliminary surrogate markers of physiological platelet dysfunction to be further studied across larger cohorts. Future studies will continue to explore those relationships and further define mechanisms of TIC and their relationship with patient outcomes.

Stored platelet hemostatic phenotype and function is not altered when donors are on testosterone replacement therapy.

BACKGROUND: Critical shortages in the national blood supply have led to a re-evaluation of previously overlooked donor sources for blood products. As a part of that effort, red blood cells collected from therapeutic phlebotomy of donors on testosterone replacement therapy (TRT) have been conditionally approved for transfusion. However, platelets from TRT donors are not currently approved for use due to limited data on effects of supraphysiologic testosterone on recipient safety and platelet function. The objective of this study was to provide a comprehensive profile of phenotype and function in platelets from TRT and control donors. STUDY DESIGN AND METHODS: Platelets in plasma were collected from TRT and control donors (N = 10 per group; age- and sex-matched) and stored at room temperature for 7 days. On storage Day 1 (D1) and Day 7 (D7), platelet products were analyzed for platelet count, metabolic parameters (i.e., glucose, lactate, mitochondrial function), surface receptor expression, aggregation, thrombin generation, and thrombus formation under physiological flow conditions. RESULTS: TRT donor platelets were not significantly different than control donor platelets in terms of count, surface phenotype, metabolic function, ability to aggregate, thrombin generation, or ability to form occlusive thrombus under arterial flow regimes. Both groups were similar to each other by D7, but had significantly lost hemostatic function compared to D1. DISCUSSION: Platelets derived from donors undergoing TRT have similar phenotypic and functional profiles compared to those derived from control donors. This suggests that therapeutic phlebotomy of TRT donors may provide a useful source for platelet products.

Testosterone supplementation increases red blood cell susceptibility to oxidative stress, decreases membrane deformability, and decreases survival after cold storage and transfusion.

BACKGROUND: Blood collection from donors on testosterone therapy (TT) is restricted to red blood cell (RBC) concentrates to avoid patient exposure to supraphysiological testosterone (T). The objective of this study was to identify TT-related changes in RBC characteristics relevant to transfusion effectiveness in patients. STUDY DESIGN: This was a two-part study with cohorts of patients and blood donors on TT. In part 1, we conducted longitudinal evaluation of RBCs collected before and at three time points after initiation of T. RBC assays included storage and oxidative hemolysis, membrane deformability (elongation index), and oximetry. In part 2, we evaluated the fate of transfused RBCs from TT donors in immunodeficient mice and by retrospective analyses of NIH's vein-to-vein databases. RESULTS: TT increased oxidative hemolysis (1.45-fold change) and decreased RBC membrane deformability. Plasma free testosterone was positively correlated with oxidative hemolysis (r = .552) and negatively correlated with the elongation index (r = -.472). Stored and gamma-irradiated RBCs from TT donors had lower posttransfusion recovery in mice compared to controls (41.6 ± 12 vs. 55.3 ± 20.5%). Recipients of RBCs from male donors taking T had 25% lower hemoglobin increments compared to recipients of RBCs from non-TT male donors, and had increased incidence (OR, 1.80) of requiring additional RBC transfusions within 48 h of the index transfusion event. CONCLUSIONS: TT is associated with altered RBC characteristics and transfusion effectiveness. These results suggest that clinical utilization of TT RBCs may be less effective in recipients who benefit from longer RBC survival, such as chronically transfused patients.