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Heme oxygenase-1 and carbon monoxide suppress the pathogenesis of experimental cerebral malaria


Cerebral malaria claims more than 1 million lives per year. We report that heme oxygenase-1 (HO-1, encoded by Hmox1) prevents the development of experimental cerebral malaria (ECM). BALB/c mice infected with Plasmodium berghei ANKA upregulated HO-1 expression and activity and did not develop ECM. Deletion of Hmox1 and inhibition of HO activity increased ECM incidence to 83% and 78%, respectively. HO-1 upregulation was lower in infected C57BL/6 compared to BALB/c mice, and all infected C57BL/6 mice developed ECM (100% incidence). Pharmacological induction of HO-1 and exposure to the end-product of HO-1 activity, carbon monoxide (CO), reduced ECM incidence in C57BL/6 mice to 10% and 0%, respectively. Whereas neither HO-1 nor CO affected parasitemia, both prevented blood-brain barrier (BBB) disruption, brain microvasculature congestion and neuroinflammation, including CD8+ T-cell brain sequestration. These effects were mediated by the binding of CO to hemoglobin, preventing hemoglobin oxidation and the generation of free heme, a molecule that triggers ECM pathogenesis.

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Figure 1: Expression of HO-1 prevents the pathogenesis of ECM in BALB/c mice infected with P. berghei ANKA.
Figure 2: Induction of HO-1 or exposure to CO suppresses ECM onset in C57BL/6 mice infected with P. berghei ANKA.
Figure 3: HO-1 and CO prevent BBB disruption and brain microvascular congestion.
Figure 4: CO inhibits neuroinflammation and CD8+ T-cell brain sequestration.
Figure 5: HO-1 and CO prevent BBB disruption and the development of ECM by inhibiting free heme release from oxidized hemoglobin.
Figure 6: Mechanism underlying the protective actions of HO-1 and CO.


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We thank S.-F. Yet (Pulmonary and Critical Care Division, Brigham and Women's Hospital) for providing the original Hmox1 mouse breeding pairs from which all Hmox1−/− used in this study were derived. We also thank A. Rodriguez, F. Bach, T. Pais and C. Gregoire for critically reviewing the manuscript, S. Rebelo for performing the mouse breeding and genotyping, Departamento de Anatomia Patológica (Universidade de Lisboa) for help in histopathology studies, and N. Sepúlveda for statistical analysis. This work was partially supported by Fundação para a Ciência e Tecnologia (POCTI/SAU-IMI/57946/2004 to M.M.M. and POCTI/SAU-MNO/56066/2004 to M.P.S.), the European Science Foundation (EURYI 2004 to M.M.M.), the Gemi Fund (to M.M.M.) and by the Hungarian government (OTKA-61546 and RET-2/2 to J.B.). A.P., A.F., C.D.R., A.C., S.E. and M.C.R. were supported by Fundação para a Ciência e Tecnologia fellowships (BPD/10510/2002, BPD/21707/2005, BD/14232/2003, BD/3106/2000, BPD/12188/2003 and BD/8435/2002, respectively). M.M.M. is a fellow of the EMBO Young Investigator Program and is a Howard Hughes Medical Institute International Research Scholar.

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Authors and Affiliations



A.P. performed the majority of the experimental work. A.F. contributed critically to defining the role of free heme in the onset of ECM. Both A.P. and A.F. contributed to the study design and helped in drafting the manuscript. J.B., V.J. and G.B. performed the in vitro studies that defined the ability of CO to inhibit hemoglobin oxidation. S.E. performed all histological procedures and analysis. A.C., C.D.R., I.P.G., M.C.-R. and S.P. contributed to the experimental work. M.M.M. formulated the initial hypothesis that HO-1 and CO might counter the onset of ECM, and M.P.S. formulated the hypothesis that CO might act on hemoglobin to arrest ECM triggered by free heme. Both M.P.S. and M.M.M. conceived and designed the experimental procedures and wrote the manuscript. All authors read and approved the manuscript.

Corresponding authors

Correspondence to Miguel P Soares or Maria M Mota.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Kinetics of HO-1 and HO-2 protein expression in the brain during malaria infection. (PDF 168 kb)

Supplementary Fig. 2

HO-1 expression in the liver and lungs during malaria infection. (PDF 97 kb)

Supplementary Fig. 3

CO, but not biliverdin, suppresses the pathogenesis of ECM. (PDF 90 kb)

Supplementary Fig. 4

Assessment of BBB disruption and parenchymal brain hemorrhage in P. berghei ANKA infected mice. (PDF 883 kb)

Supplementary Fig. 5

CO prevents Hb oxidation. (PDF 95 kb)

Supplementary Fig. 6

CO does not inhibit red blood cell lysis. (PDF 95 kb)

Supplementary Fig. 7

Correlation between circulating free-heme and susceptibility to ECM. (PDF 122 kb)

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Pamplona, A., Ferreira, A., Balla, J. et al. Heme oxygenase-1 and carbon monoxide suppress the pathogenesis of experimental cerebral malaria. Nat Med 13, 703–710 (2007).

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