Hypomorphic biliverdin reductase a mutations define bilirubin anti-malarial threshold.

Jaundice, a condition characterized by elevated circulating bilirubin generated by biliverdin reductase A (BVRA), is protective against malaria. Beyond its oxidoreductase activity, BVRA acts as a protein kinase and transcriptional regulator. To probe the protective effect of BVRA oxidoreductase activity, we generated mice harboring G17A and E97A missense mutations in its NAD(P)H-binding and reductase motifs, respectively. BVRA oxidoreductase activity was reduced by ∼95% and ∼80%-90% in Blvra G17A and Blvra E97A vs. wild-type (Blvra WT) mice, respectively. Plasmodium chabaudi chabaudi AS (Pcc) infection was lethal in Blvra G17A and Blvra E97A, compared to the non-lethal outcome in control Blvra WT mice. Quantification of circulating unconjugated bilirubin in Pcc-infected mice revealed dose response effect whereby the mutant strains failed to reach a protective ∼20-30 μM (∼1-2 mg/dL) threshold. These findings establish the antimalarial effect of BVRA oxidoreductase activity and define a threshold of circulating bilirubin required for malaria protection, informing on therapeutic development and biomarker-guided strategies.