Dr. Thomas Divers
Endotoxemia is a severe complication of many common equine disorders. The patient populations at high risk include horses with gastrointestinal inflammatory disease or recovering from abdominal surgery, mares with metritis, and foals with failure of passive transfer. Rather than direct cellular toxicity, endotoxin evokes a dysregulated inflammatory response characterized by widespread leukocyte mobilization, activation, and release of cytokine cascades. Moreover, leukocyte-derivedmetalloproteinases are implicated in the development of laminitis. Recent studies reveal that endotoxin acts as a platelet agonist, thereby promoting cross-activation of coagulation thatexacerbates tissue injury due to microvascular thrombosis.
Our broad objective is to develop a treatment strategy targeting platelet activation as a critical control point modulating host response to endotoxin. In this pilot project we will evaluate the anti-platelet drug clopidogrel bisulfate (Plavix®).
The specific aims of the proposed 1-year project are:
1. Test the effects of endotoxemia on equine platelet activation status
2. Determine whether administration of clopidogrel (a platelet ADP-receptor antagonist) can block pro-inflammatory and/or pro-coagulant effects of endotoxin.
We will utilize an established endotoxemia model of lipopolysaccharide (LPS) infusion to healthy horses. LPS will be infused to 2 study groups (n=6 per group): Group 1 = Clopidogrel (2mg/kg PO x 72 hr) prior to LPS infusion. Group 2 = Oral placebo x 72 hr prior to LPS infusion.
Clinical parameters (e.g. TPR, comfort scores, CBC, glucose, lactate), recognized markers ofLPS-induced inflammation, and novel tests to detect LPS-induced procoagulant effects will be measured at study entry and monitored serially after infusion. Blood samples will be collected for a comprehensive test panel consisting of: TNFa, fibrinogen, monocyte tissue factor expression, platelet contribution to fibrin clot strength (thrombelastography), platelet adhesion (PFA100), platelet aggregation (optical aggregometry), platelet activation parameters of P-selectin expression, fibrinogen receptor activation, microparticle release, and phospholipid externalization (flow cytometry).
This study approach is applicable for evaluating any anti-platelet agent in the LPS model and will aid in our subsequent design of clinical trials for an effective endotoxin treatment regimen.