Histidine- rich protein II nanoparticle delivery of heme iron load drives endothelial inflammation in cerebral malaria

Histidine- rich protein II (HRPII) is secreted by Plasmodium falciparum during the blood stage of malaria infection. High plasma levels of HRPII are associated with cere -bral malaria, a severe and highly fatal complication of malaria. HRPII has been shown to induce vascular leakage, the hallmark of cerebral malaria, in blood-brain barrier (BBB) and animal models. We have discovered an important mechanism for BBB dis-ruption that is driven by unique features of HRPII. By characterizing serum from infected patients and HRPII produced by P. falciparum parasites in culture, we found that HRPII exists in large multimeric particles of 14 polypeptides that are richly laden with up to 700 hemes per particle. Heme loading of HRPII is required for efficient binding and internalization via caveolin-mediated endocytosis in hCMEC/D3 cerebral microvascular endothelial cells. Upon acidification of endolysosomes, two-thirds of the hemes are released from acid-labile binding sites and metabolized by heme oxygen-ase 1, generating ferric iron and reactive oxygen species. Subsequent activation of the NLRP3 inflammasome and IL- 1 & beta; secretion resulted in endothelial leakage. Inhibition of these pathways with heme sequestration, iron chelation, or anti-inflammatory drugs protected the integrity of the BBB culture model from HRPII:heme. Increased cerebral vascular permeability was seen after injection of young mice with heme-loaded HRPII (HRPII:heme) but not with heme-depleted HRPII. We propose that during severe malaria infection, HRPII:heme nanoparticles in the bloodstream deliver an overwhelm-ing iron load to endothelial cells to cause vascular inflammation and edema. Disrupting this process is an opportunity for targeted adjunctive therapies to reduce the morbidity and mortality of cerebral malaria.

Automated summary

Histidine-rich protein II (HRPII) secreted by Plasmodium falciparum during the blood stage of malaria infection contributes to cerebral malaria by inducing vascular leakage. HRPII, characterized by large multimeric particles laden with hemes, can bind and internalize into cerebral microvascular endothelial cells through caveolin-mediated endocytosis. The release of hemes and subsequent activation of inflammasome pathway result in endothelial leakage. Inhibiting these pathways can protect the integrity of the blood-brain barrier (BBB) and reduce the morbidity and mortality of cerebral malaria.