Novel Strategy to Combat the Procoagulant Phenotype in Heparin-Induced Thrombocytopenia Using 12-LOX Inhibition

BACKGROUND:Heparin-induced thrombocytopenia (HIT) is a major concern for all individuals that undergo cardiac bypass surgeries or require prolonged heparin exposure. HIT is a life- and limb-threatening adverse drug reaction with an immune response following the formation of ultra-large immune complexes that drive platelet activation through the receptor Fc & gamma;RIIA. Thrombotic events remain high following the standard of care treatment with anticoagulants, while increasing risk of bleeding complications. This study sought to investigate a novel approach to treatment of HIT. Recent reports demonstrate increased procoagulant activity in HIT; however, these reports required analysis ex vivo, and relevance in vivo remains unclear.METHODS:Using human and mouse model systems, we investigated the cooperativity of PARs (protease-activated receptors) and Fc & gamma;RIIA in HIT. We challenged humanized Fc & gamma;RIIA transgenic mice with or without endogenous mouse Par4 (denoted as IIA-Par4+/+ or IIA-Par4-/-, respectively) with a well-established model IgG immune complex (anti [& alpha;]-CD9). Furthermore, we assessed the procoagulant phenotype and efficacy to treat HIT utilizing inhibitor of 12-LOX (12[S]-lipoxygenase), VLX-1005, previously reported to decrease platelet activation downstream of Fc & gamma;RIIA and PAR4, using the triple allele HIT mouse model.RESULTS:IIA-Par4+/+ mice given & alpha;CD9 were severely thrombocytopenic, with extensive platelet-fibrin deposition in the lung. In contrast, IIA-Par4-/- mice had negligible thrombocytopenia or pulmonary platelet-fibrin thrombi. We observed that pharmacological inhibition of 12-LOX resulted in a significant reduction in both platelet procoagulant phenotype ex vivo, and thrombocytopenia and thrombosis in our humanized mouse model of HIT in vivo.CONCLUSIONS:These data demonstrate for the first time the need for dual platelet receptor (PAR and Fc & gamma;RIIA) stimulation for fibrin formation in HIT in vivo. These results extend our understanding of HIT pathophysiology and provide a scientific rationale for targeting the procoagulant phenotype as a possible therapeutic strategy in HIT.

Automated summary

This study investigated the cooperativity of PARs (protease-activated receptors) and Fc & gamma;RIIA in HIT using human and mouse model systems. It was found that pharmacological inhibition of 12-LOX can decrease platelet procoagulant phenotype and reduce thrombocytopenia and thrombosis in a mouse model of HIT.