Increased platelet mitochondrial function correlates with clot strength in a rodent fracture model

BACKGROUND: Thromboelastographic measures of clot strength increase early after injury, portending higher risks for thromboembolic complications during recovery. Understanding the specific role of platelets is challenging because of a lack of clinically relevant measures of platelet function. Platelet mitochondrial respirometry may provide insight to global platelet function but has not yet been correlated with functional coagulation studies. METHODS: Wistar rats underwent anesthesia and either immediate sacrifice for baseline values (n = 6) or (1) bilateral hindlimb orthopedic injury (n = 12), versus (2) sham anesthesia (n = 12) with terminal phlebotomy/hepatectomy after 24 hours. High-resolution respirometry was used to measure basal respiration, mitochondrial leak, maximal oxidative phosphorylation, and Complex IV activity in intact platelets; Complex I- and Complex II-driven respiration was measured in isolated liver mitochondria. Results were normalized to platelet number and protein mass, respectively. Citrated native thromboelastography (TEG) was performed in triplicate. RESULTS: Citrated native TEG maximal amplitude was significantly higher (81.0 +/- 3.0 vs. 73.3 +/- 3.5 mm, p < 0.001) in trauma compared with sham rats 24 hours after injury. Intact platelets from injured rats had higher basal oxygen consumption (17.7 +/- 2.5 vs. 15.1 +/- 3.2 pmol O2/[s x 108 cells], p = 0.045), with similar trends in mitochondrial leak rate (p = 0.19) when compared with sham animals. Overall, platelet basal respiration significantly correlated with TEG maximal amplitude (r = 0.44, p = 0.034). As a control for sex-dependent systemic mitochondrial differences, females displayed higher liver mitochondria Complex I-driven respiration (895.6 +/- 123.7 vs. 622.1 +/- 48.7 mmol e-/min/mg protein, p = 0.02); as a control for systemic mitochondrial effects of injury, no liver mitochondrial respiration differences were seen. CONCLUSION: Platelet mitochondrial basal respiration is increased after injury and correlates with clot strength in this rodent hindlimb fracture model. Several mitochondrial-targeted therapeutics exist in common use that are underexplored but hold promise as potential antithrombotic adjuncts that can be sensitively evaluated in this preclinical model.