The polyanionic drug suramin neutralizes histones and prevents endotheliopathy

Drugs are needed to protect against the neutrophil-derived histones responsible for endothelial injury in acute inflammatory conditions such as trauma and sepsis. Heparin and other polyanions can neutralize histones but may cause secondary, deleterious effects such as excessive bleeding. Here, we demonstrate that suramin--a widely available polyanionic drug--completely neutralizes the toxic effects of histones. The sulfate groups on suramin form stable electrostatic interactions with hydrogen bonds in the histone octamer with a dissociation constant of 250 nM. In cultured endothelial cells (Ea.Hy926), histone-induced thrombin generation was significantly decreased by suramin. In isolated murine blood vessels, suramin abolished aberrant endothelial cell calcium signals and rescued impaired endothelial-dependent vasodilation caused by histones. Suramin significantly decreased pulmonary endothelial cell ICAM-1 expression and neutrophil recruitment caused by infusion of sub-lethal doses of histones in vivo. Suramin also prevented lung edema, intra-alveolar hemorrhage and mortality in mice receiving a lethal dose of histones. Protection of vascular endothelial function from histone-induced damage is a novel mechanism of action for suramin with therapeutic implications for conditions characterized by elevated histone levels. Significance StatementPathologic levels of circulating histones cause acute endotheliopathy, characterized by widespread disruption of critical endothelial functions and thromboinflammation. We discovered that suramin binds histones and prevents histone-induced endothelial dysfunction, thrombin generation, lung injury, and death. Histone binding is a novel mechanism of action for suramin, considered among the safest and most effective drugs by the World Health Organization. These results support the use of suramin for protection of blood vessels in conditions exacerbated by circulating histones including trauma and sepsis.