Parasite histones are toxic to brain endothelium and link blood barrier breakdown and thrombosis in cerebral malaria.

Microvascular thrombosis and blood-brain barrier (BBB) breakdown are key components of cerebral malaria (CM) pathogenesis in African children and are implicated in fatal brain swelling. How Plasmodium falciparum infection causes this endothelial disruption and why this occurs, particularly in the brain, is not fully understood. In this study, we have demonstrated that circulating extracellular histones, equally of host and parasite origin, are significantly elevated in CM patients. Higher histone levels are associated with brain swelling on magnetic resonance imaging. On postmortem brain sections of CM patients, we found that histones are colocalized with P falciparum-infected erythrocytes sequestered inside small blood vessels, suggesting that histones might be expelled locally during parasite schizont rupture. Histone staining on the luminal vascular surface colocalized with thrombosis and leakage, indicating a possible link between endothelial surface accumulation of histones and coagulation activation and BBB breakdown. Supporting this, patient sera or purified P falciparum histones caused disruption of barrier function and were toxic to cultured human brain endothelial cells, which were abrogated with antihistone antibody and nonanticoagulant heparin. Overall, our data support a role for histones of parasite and host origin in thrombosis, BBB breakdown, and brain swelling in CM, processes implicated in the causal pathway to death. Neutralizing histones with agents such as nonanticoagulant heparin warrant exploration to prevent brain swelling in the development or progression of CM and thereby to improve outcomes.

The clinical utility of fibrin-related biomarkers in sepsis.

Sepsis is associated with systemic inflammatory responses and induction of intravascular fibrin formation. Our aim is to investigate whether three fibrin-related markers (FRM) reflect the extent of coagulation activation in vivo and evaluate their clinical usefulness in identifying as well as monitoring patients with sepsis. Fibrin-degradation products (FDP), D-dimer and soluble fibrin monomer assays were measured on plasma samples from patients in the ICU with sepsis (n = 37), systemic inflammatory response syndrome (SIRS) (n = 35) and healthy individuals (n = 15). The levels were correlated with each other and also with fibrinogen, prothrombin time, platelets and antithrombin III. Clinical correlation was also performed for the diagnosis of sepsis and longitudinal monitoring for survival or death.There was strong correlation between the three FRM (r = 0.38-0.93, P < 0.0001) with only fibrin monomer correlating significantly with prothrombin time, fibrinogen and platelet levels. Clinically, all three FRM could discriminate between patients with sepsis, SIRS and healthy individuals with FDP, and D-dimer showing statistical significance (P < 0.05). No FRM predicted outcome from a single measurement but FDP was significantly able to predict patient survival from serial samples [mean FDP (µg/ml) from 35.36 to 21.37 (first to third ICU-day), P < 0.05]. Fibrin monomer appears the most sensitive indicator of coagulation activation, whereas D-dimer and FDP levels can significantly differentiate ICU patients with sepsis from those without. In addition, FDP would be preferable for monitoring with its statistically significant time-dependent prediction of survival or death from sepsis.