Pulmonary manifestations of malaria : recognition and management

Malarial infection develops mitochondrial pathology and mitochondrial oxidative stress to promote hepatocyte apoptosis

Activation of the mitochondrial apoptosis pathway by oxidative stress has been implicated in hepatocyte apoptosis during malaria. Because mitochondria are the source and target of reactive oxygen species (ROS), we have investigated whether hepatocyte apoptosis is linked to mitochondrial pathology and mitochondrial ROS generation during malaria. Malarial infection induces mitochondrial pathology by inhibiting mitochondrial respiration, dehydrogenases, and transmembrane potential and damaging the ultrastructure as evident from transmission electron microscopic studies. Mitochondrial GSH depletion and formation of protein carbonyl indicate that mitochondrial pathology is associated with mitochondrial oxidative stress. Fluorescence imaging of hepatocytes documents intramitochondrial superoxide anion (O(2)(-)) generation during malaria. O(2)(-) inactivates mitochondrial aconitase to release iron from iron-sulfur clusters, which forms the hydroxyl radical ((.)OH) interacting with H(2)O(2) produced concurrently. Malarial infection inactivates mitochondrial aconitase, and carbonylation of aconitase is evident from Western immunoblotting. The release of iron has been documented by fluorescence imaging of hepatocytes using Phen Green SK, and mitochondrial (.)OH generation has been confirmed. During malaria, the depletion of cardiolipin and formation of the mitochondrial permeability transition pore favor cytochrome c release to activate caspase-9. Interestingly, mitochondrial (.)OH generation correlates with the activation of both caspase-9 and caspase-3 with the progress of malarial infection, indicating the critical role of (.)OH.

Parasite burden and CD36-mediated sequestration are determinants of acute lung injury in an experimental malaria model

Although acute lung injury (ALI) is a common complication of severe malaria, little is known about the underlying molecular basis of lung dysfunction. Animal models have provided powerful insights into the pathogenesis of severe malaria syndromes such as cerebral malaria (CM); however, no model of malaria-induced lung injury has been definitively established. This study used bronchoalveolar lavage (BAL), histopathology and gene expression analysis to examine the development of ALI in mice infected with Plasmodium berghei ANKA (PbA). BAL fluid of PbA-infected C57BL/6 mice revealed a significant increase in IgM and total protein prior to the development of CM, indicating disruption of the alveolar–capillary membrane barrier—the physiological hallmark of ALI. In contrast to sepsis-induced ALI, BAL fluid cell counts remained constant with no infiltration of neutrophils. Histopathology showed septal inflammation without cellular transmigration into the alveolar spaces. Microarray analysis of lung tissue from PbA-infected mice identified a significant up-regulation of expressed genes associated with the gene ontology categories of defense and immune response. Severity of malaria-induced ALI varied in a panel of inbred mouse strains, and development of ALI correlated with peripheral parasite burden but not CM susceptibility. Cd36^−/− mice, which have decreased parasite lung sequestration, were relatively protected from ALI. In summary, parasite burden and CD36-mediated sequestration in the lung are primary determinants of ALI in experimental murine malaria. Furthermore, differential susceptibility of mouse strains to malaria-induced ALI and CM suggests that distinct genetic determinants may regulate susceptibility to these two important causes of malaria-associated morbidity and mortality.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) can occur in adult malaria infections with a case fatality rate of 70%–100%. ALI and ARDS are characterized by protein-rich fluid in the lungs, with reduced gas exchange, and in malaria, often accompany high parasite levels and severe or cerebral disease. In this work we have examined lung physiology, pathology and genomics in mouse malaria—Plasmodium berghei ANKA—to show that mice develop malaria-induced ALI. Infected mice have proteinaceous fluid in their lungs, have a migration of inflammatory cells from the blood into the lung walls, and express immune response–related genes. We also found that severity of ALI depended on high parasite levels, both overall and specifically in the lung tissue, but was not consistent with whether the mice developed cerebral malaria. ALI due to Plasmodium berghei ANKA infection models prominent characteristics of human malaria-associated ALI, and we have better defined this model of malaria ALI so it may be used to further explore disease mechanisms and eventual treatment.

Shared features in the pathobiology of babesiosis and malaria

The pathobiology of malaria has been extensively studied in humans but many questions remain, especially regarding fulminant disease associated with Plasmodium falciparum infection. Babesiosis, recognized since biblical times as an important disease of livestock and more recently as an emerging health problem in humans, is caused by related intraerythrocytic protozoa with a similar pathogenesis and clinical course. Recent studies of cytokine activation and erythrocyte cytoadherence in babesiosis and malaria have exploited these similarities to provide new insights into malaria pathobiology. Continued investigation of similarities and differences in the pathogenesis of babesiosis and malaria should lead to additional fundamental insights for both conditions.

Src-family kinase dependent disruption of endothelial barrier function by Plasmodium falciparum merozoite proteins

Pulmonary complication in severe Plasmodium falciparum malaria is manifested as a prolonged impairment of gas transfer or the more severe acute respiratory distress syndrome (ARDS). In either clinical presentation, vascular permeability is a major component of the pathologic process. In this report, we examined the effect of clinical P falciparum isolates on barrier function of primary dermal and lung microvascular endothelium in vitro. We showed that parasite sonicates but not intact infected erythrocytes disrupted endothelial barrier function in a Src-family kinase-dependent manner. The abnormalities were manifested both as discontinuous immunofluorescence staining of the junctional proteins ZO-1, claudin 5, and VE-cadherin and the formation of interendothelial gaps in monolayers. These changes were associated with a loss in total protein content of claudin 5 and redistribution of ZO-1 from the cytoskeleton to the membrane and the cytosolic and nuclear fractions. There was minimal evidence of a proinflammatory response or direct cellular cytotoxicity or cell death. The active component in sonicates appeared to be a merozoite-associated protein. Increased permeability was also induced by P falciparum glycophosphatidylinositols (GPIs) and food vacuoles. These results demonstrate that parasite components can alter endothelial barrier function and thus contribute to the pathogenesis of severe falciparum malaria.