Caspase-1 activation drives vascular inflammatory processes and hypoperfusion in intravascular hemolysis

Intravascular hemolysis (IVH), a pathological process associated with various conditions, triggers inflammatory responses, yet the key molecular drivers of these responses are poorly defined, particularly within the vasculature. To explore the role of NLRP3 inflammasome- and caspase-1-dependent pathways in IVH-induced vascular dysfunction, we used in vivo models of acute and chronic IVH, alongside heme stimulation of endothelial cells, thereby isolating this disease mechanism from its etiological causes. IVH induced rapid inflammatory responses in C57BL/6J mice, including interleukin (IL)-1β release within 15 min, and NLRP3-dependent caspase-1 activation in circulating leukocytes. Chronic IVH elevated hepatic NLRP3 protein expression and caspase-1 activity in monocyte-derived macrophages. In turn, acute IVH significantly impaired cutaneous microvascular blood flow and perfusion and triggered microvascular leukocyte recruitment, both via caspase-1-dependent mechanisms. Consistently, caspase-1-knockout mice did not demonstrate hypoperfusion following IVH and pharmacological inhibition of caspase-1 in sickle cell disease mice, which display continuous moderate hemolysis, attenuated heme-induced vaso-occlusion. IVH also upregulated leukocyte CD11b-integrin expression in vivo, whereas heme simulation of endothelial cells promoted inflammatory mediator release and caspase-1 activation, potentially facilitating leukocyte recruitment. Although the leukocyte alarmin S100A8, released during IVH, amplified IL-1β release in the presence of heme, reactive oxygen species generation, rather than caspase-1 activation, was required for endothelial adhesion molecule expression. Together, these findings identify caspase-1 activation as a key driver of hemolysis-induced microvascular leukocyte recruitment and hypoperfusion, potentially facilitating the progression of skin lesions and organ damage. Targeting caspase-dependent pathways may be of therapeutic potential for limiting vascular inflammation and tissue injury in IVH-associated conditions.NEW & NOTEWORTHY This study identifies caspase-1 as a driver of the microvascular leukocyte recruitment and hypoperfusion that is induced by intravascular hemolysis (IVH). Using in vivo models and heme-stimulated endothelial cells, we show that IVH rapidly induces caspase-1-dependent endothelial-leukocyte recruitment, microvascular dysfunction, and also IL-1β release. Oxidative stress promotes heme-induced endothelial caspase-1 activation and adhesion molecule expression, potentially amplifying vascular dysfunction. These findings provide insight into IVH-driven pathology in hemolytic disorders, including sickle cell disease.