A Metabolite-Based Resistance Mechanism Against Malaria
Severe presentations of malaria, arising from Plasmodium spp. infection, are often associated with accumulation of circulating bilirubin, a condition known as hyperbilirubinemia or jaundice of malaria. Whether this represents an adaptive or maladaptive response to Plasmodium spp. infection is not understood. Departing from the textbook view of hyperbilirubinemia reflecting a failure to excrete bilirubin, we demonstrate that bilirubin production by biliverdin reductase A (BLVRA) partakes in a host adaptive response to malaria. Genetic Blvra deletion exacerbated malaria mortality in mice; This was associated with a >10-fold increase in parasite burden, compared to control mice expressing BLVRA, which cleared the parasite and survived malaria. At concentrations in the range of jaundice of malaria, unconjugated bilirubin arrested the proliferation and killed asexual blood stages of the human-infective P. falciparum in vitro. This was associated with disruption of the parasite's mitochondrion and food vacuole as well as with the accumulation of hemozoin in the parasite's cytoplasm. Moreover, bilirubin inhibited hemozoin (ß-hematin) synthesis in vitro, a vital heme-detoxifying pathway targeted by Quinoline-based antimalarial drugs such as chloroquine. In conclusion, hyperbilirubinemia represents an evolutionary conserved metabolite-based resistance mechanism against malaria. Overall design: Mouse response to the infection of Plasmodium chabaudi chabaudi AS (Pcc AS) in Blvra+/+ wild-type and Blvra-/- knockout genotypes. Briefly, Blvra+/+ and Blvra-/- mouse blood samples were collected after 7 days of infection (i.e., peak of infection) and infected red blood samples were sorted. Sequencing reads were mapped against the Pcc AS genome.