Direct Interleukin-6 Inhibition Blunts Arterial Thrombosis by Reducing Collagen-Mediated Platelet Activation.

BACKGROUND: Recent clinical trials demonstrated a reduction in biomarkers of thrombosis and inflammation in patients with very high cardiovascular risk treated with the anti-IL-6 (interleukin 6) monoclonal antibody ziltivekimab. However, if and how direct IL-6 inhibition exerts antithrombotic effects remains unknown. This translational project aimed to investigate the effect of direct IL-6 inhibition on experimental arterial thrombus formation and its underlying cellular mechanisms. METHODS: Three-month-old C57BL/6J male and female mice received very low dose lipopolysaccharide for 4 weeks; in addition to lipopolysaccharide, during the fourth week, mice were randomized to receive either anti-mouse IL-6 monoclonal antibody 200 μg or IgG1 isotype control. Thrombosis of the right common carotid artery was induced by endothelial-targeted laser injury. Coagulation factors and platelet reactivity were assessed in treated mice and controls. Platelets were isolated from whole blood and their reactivity to different chemical stimuli was measured by fluorescence-activated cell sorting. Additionally, whole blood samples from patients with a history of percutaneous coronary intervention were incubated ex vivo with either ziltivekimab biosimilar or IgG1 isotype control. Platelet reactivity at rest and in response to diverse chemical stimuli was quantified by fluorescence-activated cell sorting. RESULTS: Mice with low-grade chronic inflammation treated with anti-IL-6 monoclonal antibody displayed significantly blunted thrombus formation, without any significant difference in coagulation factors. Ex vivo stimulation with Collagen-rP (collagen-related peptide) significantly activated platelets isolated from control mice but not those obtained from mice treated with anti-IL-6 monoclonal antibody. Similarly, platelet reactivity from patients with previous percutaneous coronary intervention fell significantly after ex vivo treatment with ziltivekimab biosimilar. CONCLUSIONS: Direct IL-6 inhibition blunts thrombus formation by reducing collagen-induced platelet activation. These findings offer a potential mechanistic explanation for the results observed in the RESCUE trial and support the rationale of the ongoing ZEUS trial (Ziltivekimab Cardiovascular Outcome Study).