Brain hemodynamics in cerebral malaria (CM) is poorly understood , with apparently conflicting data showing microcirculatory hypoperfusion and normal or even increased blood flow in large arteries. Using intravital microscopy to assess the pial microvasculature through a closed cranial window in the murine model of CM by Plasmodium berghei ANKA , we show that murine CM is associated with marked decreases (mean: 60%) of pial arteriolar blood flow attributable to vasoconstriction and decreased blood velocity. Leukocyte sequestration further decreased perfusion by narrowing luminal diameters in the affected vessels and blocking capillaries. Remarkably , vascular collapse at various degrees was observed in 44% of mice with CM , which also presented more severe vasoconstriction. Coadministration of artemether and nimodipine , a calcium channel blocker used to treat postsubarachnoid hemorrhage vasospasm, to mice presenting CM markedly increased survival compared with artemether plus vehicle only. Administration of nimodipine induced vasodilation and increased pial blood flow. We conclude that vasoconstriction and vascular collapse play a role in murine CM pathogenesis and nimodipine holds potential as adjunctive therapy for CM.

Cerebral malaria (CM) is a leading cause of death in Plasmodium falciparum infections. In the Plasmodium berghei ANKA (PbA) murine model, CM pathogenesis is associated with low nitric oxide (NO) bioavailability and brain microcirculatory complications, with a marked decrease in cerebral blood flow, vasoconstriction, vascular plugging by adherent cells, and hemorrhages. Using intravital microscopy through a closed cranial window, here we show that NO supplementation in the form of a NO donor (dipropylenetriamine NONOate [DPTA-NO]) prevented vasoconstriction and improved blood flow in pial vessels of PbA-infected mice. Arterioles and venules of smaller diameters (20-35.5 μm) showed better response to treatment than vessels of larger diameters (36-63 μm). Exogenous NO provided protection against brain hemorrhages (mean, 1.4 vs 24.5 hemorrhagic foci per section) and inflammation (mean, 2.5 vs 10.9 adherent leukocytes per 100 μm vessel length) compared with saline treatment. In conclusion, NO protection against CM is associated with improved brain microcirculatory hemodynamics and decreased vascular pathology.

The murine model of cerebral malaria (ECM) caused by Plasmodium berghei ANKA (PbA) infection in susceptible mice has been extensively used for studies of pathogenesis and identification of potential targets for human CM therapeutics. However, the model has been seldom explored to evaluate adjunctive therapies for this malaria complication. A first step toward this goal is to define a treatment protocol with an effective antimalarial drug able to rescue mice presenting late-stage ECM. We evaluated the efficacy of artemisinin, artemether, artesunate, and quinine given intraperitoneally once a day, and combinations with mefloquine, in suppressing PbA infection in mice with moderate parasitemia. Artemether, artesunate, and quinine were then evaluated for efficacy in rescuing PbA-infected mice with ECM, strictly defined by using objective criteria based on the presentation of clinical signs of neurological involvement, degree of hypothermia, and performance in a set of six motor behavior tests. Artemether at 25 mg/kg presented the fastest parasite killing ability in 24 h and fully avoided recrudescence in a 5-day treatment protocol. Artemether and artesunate were equally effective in rescuing mice with late-stage ECM (46 and 43% survival, respectively), whereas quinine had a poor performance (12.5% survival). Artemether caused a marked decrease in brain leukocyte accumulation 24 h after the first dose. In conclusion, artemether and artesunate are effective in rescuing mice with late-stage ECM and decrease brain inflammation. In addition, the described protocols for more strict clinical evaluation and for rescue treatment provide a framework for studies of CM adjunctive therapies using this mouse model.

BackgroundImmune responses to malaria blood stage infection are in general defective, with the need for long-term exposure to the parasite to achieve immunity, and with the development of immunopathology states such as cerebral malaria in many cases. One of the potential reasons for the difficulty in developing protective immunity is the poor development of memory responses. In this paper, the potential association of cellular reactivity in lymphoid organs (spleen, lymph nodes and Peyer's patches) with immunity and pathology was evaluated during Plasmodium berghei ANKA infection in CBA mice.MethodsCBA mice were infected with 1 × 106 P. berghei ANKA-parasitized erythrocytes and killed on days 3, 6–8 and 10 of infection. The spleen, lymph nodes and Peyer's patches were collected, fixed in Carson's formalin, cut in 5 μm sections, mounted in glass slides, stained with Lennert's Giemsa and haematoxylin-eosin and analysed with bright-field microscopy.ResultsEarly (day 3) strong activation of T cells in secondary lymphoid organs was observed and, on days 6–8 of infection, there was overwhelming activation of B cells, with loss of conventional germinal center architecture, intense centroblast activation, proliferation and apoptosis but little differentiation to centrocytes. In the spleen, the marginal zone disappeared and the limits between the disorganized germinal center and the red pulp were blurred. Intense plasmacytogenesis was observed in the T cell zone.ConclusionThe observed alterations, especially the germinal center architecture disturbance (GCAD) with poor centrocyte differentiation, suggest that B cell responses during P. berghei ANKA infection in mice are defective, with potential impact on B cell memory responses.