Abstract

Cerebral Malaria (CM) is a severe manifestation of malaria that commonly occurs in children and is hallmarked by neurologic symptoms and significant Plasmodium falciparum parasitemia. It is currently hypothesized that cerebral hypoperfusion from impaired microvascular oxygen transport secondary to parasitic occlusion of the microvasculature is responsible for cerebral ischemia and thus disease severity. Animal models to study CM, are known as Experimental Cerebral Malaria (ECM) and include the C57BL/6J infected with Plasmodium berghei ANKA (PbA), which is ECM susceptible, and BALB/c infected with PbA, which is ECM resistant. Here we sought to investigate whether changes in Oxygen (O₂) delivery, O₂ flux and O₂ utilization are altered in both these models of ECM using Phosphorescence Quenching Microscopy (PQM) and direct measurement of microvascular hemodynamics using the cranial window preparation. Animal groups used for investigation consisted of ECM susceptible C57BL/6 (Infected, n=14) and ECM resistant BALB/c (Infected, n=9) mice. Uninfected C57BL/6 (n=6) and BALB/c (n=6) mice were included as uninfected controls. Control animals were manipulated in the exact same way as the infected mice (except for the infection itself). C57BL/6 ECM animals at day 6 of infection were divided into two cohorts: Early stage ECM, presenting mild to moderate drops in body temperature (>34°C<36°C) and late stage ECM, showing marked drops in body temperature (<33°C). Data were analyzed using a general linear mixed model. We constructed three general linear mixed models, one for total O₂ content, another for total O₂ delivery and the third for total O₂ content as a function of convective flow. We found that in both the ECM-susceptible C57BL/6J model and ECM resistant BALB/c model of CM, convective and diffusive O₂ flux along with pial hemodynamics are impaired. We further show that concomitant changes in p50 (oxygen partial pressure for 50% hemoglobin saturation), only 5 mmHg in the case of late stage CM C57BL/6J mice and O₂ diffusion result in insufficient O₂ transport by the pial microcirculation and that both these changes are required for late stage disease. In summary, we found impaired O₂ transport and O₂ affinity in late stage ECM, but only the former in either early stage ECM and ECM resistant strains.

Keywords: Cerebral malaria, Phosphorescence quenching microscopy, Microcirculation, Hemodynamics, Oxygen affinity