These observations prompt a modification of the current paradigms of the pathogenesis of malaria and clear the way to investigate the pathophysiology of P. vivax infections.

Violacein is a violet pigment extracted from the gram-negative bacterium Chromobacterium violaceum. It presents bactericidal, tumoricidal, trypanocidal, and antileishmanial activities. We show that micromolar concentrations efficiently killed chloroquine-sensitive and -resistant Plasmodium falciparum strains in vitro; inhibited parasitemia in vivo, even after parasite establishment; and protected Plasmodium chabaudi chabaudiinfected mice from a lethal challenge.Violacein is a violet pigment isolated from Chromobacterium violaceum, a gram-negative betaproteobacterium found in the Amazon River in Brazil. It has been reported to kill bacteria (4) and induces apoptosis in various types of cancer cells (1,5,7,8,10,11). Moderate activity against Trypanosoma cruzi and Leishmania amazonensis promastigotes has also been observed (3, 9). Due to the widespread presence of drug resistance in the malaria parasite, resulting in dramatically decreased efficacy of available antimalarial drugs (15), and the fact that immunoprotection achieved by the most successful malaria vaccine is only partial and short-lived (14), we evaluated the in vitro and in vivo effects of violacein on human and murine blood stage forms of Plasmodium parasites.Isolation and purification of violacein, (Fig. 1), from C. violaceum (CCT3496) were performed as previously described (12). Toxicity was measured as the concentration-dependent lysis of normal erythrocytes (NE) by counting red blood cells per milliliter with the aid of a Neubauer chamber. After 48 h of exposure to various concentrations of violacein, the percent red blood cell density (RBCD) relative to that of the control (without violacein) was monitored and calculated according to the formula (RBCD per milliliter in the presence of violacein/RBCD per milliliter without violacein) ϫ 100. As shown in Fig. 2A, a slight reduction in the RBCD percentage at violacein concentrations of Ͼ8.0 M was observed. Significant (Mann-Whitney U test, P Ͻ 0.05) toxicity to NE occurred at a concentration of 14.0 M.Next, we performed dose-response assays to obtain the 50% inhibitory concentrations (IC 50 s) of violacein against erythrocytes infected with chloroquine-sensitive or -resistant strains of P. falciparum (3D7 [16] or S20 [2], respectively) at 1% parasitemia and a 2% final hematocrit. We used [ 3 H]hypoxanthine (Amersham Biosciences, Amersham, United Kingdom) incorporation to assess parasite growth according to a protocol described elsewhere (13). Violacein was tested in triplicate at least three times with different batches and cells, and parasite growth was compared to that in nontreated infected erythrocytes (IE), which represented 100% parasite growth. Percent parasite growth inhibition was calculated according to the formula [1 Ϫ (cpm of treated IE Ϫ cpm of NE/cpm of nontreated IE Ϫ cpm of NE)] ϫ 100. After a 48-h incubation, violacein inhibited parasite development even at the lowest tested concentration of 0.06 M and completely abrogated parasite viability at concentrations of Ͼ1.0 M (Fig. 2B).The ...

e Sequestration of Plasmodium falciparum-infected erythrocytes (Pf-iEs) in the microvasculature of vital organs plays a key role in the pathogenesis of life-threatening malaria complications, such as cerebral malaria and malaria in pregnancy. This phenomenon is marked by the cytoadhesion of Pf-iEs to host receptors on the surfaces of endothelial cells, on noninfected erythrocytes, and in the placental trophoblast; therefore, these sites are potential targets for antiadhesion therapies. In this context, glycosaminoglycans (GAGs), including heparin, have shown the ability to inhibit Pf-iE cytoadherence and growth. Nevertheless, the use of heparin was discontinued due to serious side effects, such as bleeding. Other GAG-based therapies were hampered due to the potential risk of contamination with prions and viruses, as some GAGs are isolated from mammals. In this context, we investigated the effects and mechanism of action of fucosylated chondroitin sulfate (FucCS), a unique and highly sulfated GAG isolated from the sea cucumber, with respect to P. falciparum cytoadhesion and development. FucCS was effective in inhibiting the cytoadherence of Pf-iEs to human lung endothelial cells and placenta cryosections under static and flow conditions. Removal of the sulfated fucose branches of the FucCS structure virtually abolished the inhibitory effects of FucCS. Importantly, FucCS rapidly disrupted rosettes at high levels, and it was also able to block parasite development by interfering with merozoite invasion. Collectively, these findings highlight the potential of FucCS as a candidate for adjunct therapy against severe malaria.

BackgroundCerebral malaria (CM) is a syndrome characterized by neurological signs, seizures and coma. Despite the fact that CM presents similarities with cerebral stroke, few studies have focused on new supportive therapies for the disease. Hyperbaric oxygen (HBO) therapy has been successfully used in patients with numerous brain disorders such as stroke, migraine and atherosclerosis.Methodology/Principal FindingsC57BL/6 mice infected with Plasmodium berghei ANKA (PbA) were exposed to daily doses of HBO (100% O2, 3.0 ATA, 1–2 h per day) in conditions well-tolerated by humans and animals, before or after parasite establishment. Cumulative survival analyses demonstrated that HBO therapy protected 50% of PbA-infected mice and delayed CM-specific neurological signs when administrated after patent parasitemia. Pressurized oxygen therapy reduced peripheral parasitemia, expression of TNF-α, IFN-γ and IL-10 mRNA levels and percentage of γδ and αβ CD4+ and CD8+ T lymphocytes sequestered in mice brains, thus resulting in a reduction of blood-brain barrier (BBB) dysfunction and hypothermia.Conclusions/SignificanceThe data presented here is the first indication that HBO treatment could be used as supportive therapy, perhaps in association with neuroprotective drugs, to prevent CM clinical outcomes, including death.

BackgroundExperimental autoimmune encephalomyelitis (EAE) is used as an animal model for human multiple sclerosis (MS), which is an inflammatory demyelinating autoimmune disease of the central nervous system characterized by activation of Th1 and/or Th17 cells. Human autoimmune diseases can be either exacerbated or suppressed by infectious agents. Recent studies have shown that regulatory T cells play a crucial role in the escape mechanism of Plasmodium spp. both in humans and in experimental models. These cells suppress the Th1 response against the parasite and prevent its elimination. Regulatory T cells have been largely associated with protection or amelioration in several autoimmune diseases, mainly by their capacity to suppress proinflammatory response.Methodology/Principal FindingsIn this study, we verified that CD4+CD25+ regulatory T cells (T regs) generated during malaria infection (6 days after EAE induction) interfere with the evolution of EAE. We observed a positive correlation between the reduction of EAE clinical symptoms and an increase of parasitemia levels. Suppression of the disease was also accompanied by a decrease in the expression of IL-17 and IFN-γ and increases in the expression of IL-10 and TGF-β1 relative to EAE control mice. The adoptive transfer of CD4+CD25+ cells from P. chabaudi-infected mice reduced the clinical evolution of EAE, confirming the role of these T regs.Conclusions/SignificanceThese data corroborate previous findings showing that infections interfere with the prevalence and evolution of autoimmune diseases by inducing regulatory T cells, which regulate EAE in an apparently non-specific manner.

Cerebral malaria (CM) is a multifactorial syndrome involving an exacerbated proinflammatory status, endothelial cell activation, coagulopathy, hypoxia, and accumulation of leukocytes and parasites in the brain microvasculature. Despite significant improvements in malaria control, 15% of mortality is still observed in CM cases, and 25% of survivors develop neurologic sequelae for life-even after appropriate antimalarial therapy. A treatment that ameliorates CM clinical signs, resulting in complete healing, is urgently needed. Previously, we showed a hyperbaric oxygen (HBO)-protective effect against experimental CM. Here, we provide molecular evidence that HBO targets brain endothelial cells by decreasing their activation and inhibits parasite and leukocyte accumulation, thus improving cerebral microcirculatory blood flow. HBO treatment increased the expression of aryl hydrocarbon receptor over hypoxia-inducible factor 1-α (HIF-1α), an oxygen-sensitive cytosolic receptor, along with decreased indoleamine 2,3-dioxygenase 1 expression and kynurenine levels. Moreover, ablation of HIF-1α expression in endothelial cells in mice conferred protection against CM and improved survival. We propose that HBO should be pursued as an adjunctive therapy in CM patients to prolong survival and diminish deleterious proinflammatory reaction. Furthermore, our data support the use of HBO in therapeutic strategies to improve outcomes of non-CM disorders affecting the brain.-Bastos, M. F., Kayano, A. C. A. V., Silva-Filho, J. L., Dos-Santos, J. C. K., Judice, C., Blanco, Y. C., Shryock, N., Sercundes, M. K., Ortolan, L. S., Francelin, C., Leite, J. A., Oliveira, R., Elias, R. M., Câmara, N. O. S., Lopes, S. C. P., Albrecht, L., Farias, A. S., Vicente, C. P., Werneck, C. C., Giorgio, S., Verinaud, L., Epiphanio, S., Marinho, C. R. F., Lalwani, P., Amino, R., Aliberti, J., Costa, F. T. M. Inhibition of hypoxia-associated response and kynurenine production in response to hyperbaric oxygen as mechanisms involved in protection against experimental cerebral malaria.

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