The Cardeza Foundation for Hematologic Research, Center for Hemostasis, Thrombosis and Vascular Biology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA (S.A.R., X.Z., P.M., J.V.M., S.E.M.).
Sol Sherry Thrombosis Center and the Department of Physiology, Temple University School of Medicine, Philadelphia, PA (S.P.K.).
Arterioscler Thromb Vasc Biol. 2023 Oct;43(10):1808-1817. doi: 10.1161/ATVBAHA.123.319434. Epub 2023 Jun 22.
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 FcγRIIA. 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.
Using human and mouse model systems, we investigated the cooperativity of PARs (protease-activated receptors) and FcγRIIA in HIT. We challenged humanized FcγRIIA 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 [α]-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 FcγRIIA and PAR4, using the triple allele HIT mouse model.
IIA-Par4 mice given αCD9 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.
These data demonstrate for the first time the need for dual platelet receptor (PAR and FcγRIIA) 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.
肝素诱导的血小板减少症（HIT）是所有接受心脏搭桥手术或需要长时间暴露于肝素的个体的主要关注点。HIT 是一种危及生命和肢体的药物不良反应，免疫反应后形成超大免疫复合物，通过受体 FcγRIIA 驱动血小板激活。尽管采用抗凝剂进行标准治疗后血栓事件仍然很高，但出血并发症的风险增加。本研究旨在探讨一种治疗 HIT 的新方法。最近的报告表明，HIT 中存在促凝活性增加；然而，这些报告需要进行离体分析，其体内相关性尚不清楚。
我们使用人和小鼠模型系统研究了 HIT 中 PAR（蛋白酶激活受体）和 FcγRIIA 的协同作用。我们用一种已建立的模型 IgG 免疫复合物（抗 [α]-CD9）挑战有或没有内源性小鼠 Par4 的人源化 FcγRIIA 转基因小鼠（分别表示为 IIA-Par4 或 IIA-Par4）。此外，我们使用三重等位基因 HIT 小鼠模型，评估了 12-LOX（12[S]-脂加氧酶）抑制剂 VLX-1005 的促凝表型和治疗 HIT 的效果，该抑制剂先前已被报道可减少 FcγRIIA 和 PAR4 下游的血小板激活。
给予 αCD9 的 IIA-Par4 小鼠严重血小板减少，肺中有广泛的血小板-纤维蛋白沉积。相比之下，IIA-Par4 小鼠的血小板减少或肺内血小板-纤维蛋白血栓则可以忽略不计。我们观察到，12-LOX 的药理学抑制导致我们的 HIT 人源化小鼠模型中体外血小板促凝表型以及血小板减少和血栓形成显著减少。
这些数据首次证明了在体内形成 HIT 中的纤维蛋白需要双重血小板受体（PAR 和 FcγRIIA）刺激。这些结果扩展了我们对 HIT 病理生理学的理解，并为靶向促凝表型作为 HIT 可能的治疗策略提供了科学依据。
