BackgroundMalaria triggers a high inflammatory response in the host that mediates most of the associated pathologies and contributes to death. The identification of pro-inflammatory molecules derived from Plasmodium is essential to understand the mechanisms of pathogenesis and to develop targeted interventions. Uric acid derived from hypoxanthine accumulated in infected erythrocytes has been recently proposed as a mediator of inflammation in rodent malaria.Methods and FindingsWe found that human erythrocytes infected with Plasmodium falciparum gradually accumulate hypoxanthine in their late stages of development.To analyze the role of hypoxanthine-derived uric acid induced by P. falciparum on the inflammatory cytokine response from human blood mononuclear cells, cultures were treated with allopurinol, to inhibit uric acid formation from hypoxanthine, or with uricase, to degrade uric acid. Both treatments significantly reduce the secretion of TNF, IL-6, IL-1β and IL-10 from human cells.Conclusions and SignificanceUric acid is a major contributor of the inflammatory response triggered by P. falciparum in human peripheral blood mononuclear cells. Since the inflammatory reaction induced by P. falciparum is considered a major cause of malaria pathogenesis, identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

Malaria, which is caused by Plasmodium parasite erythrocyte infection, is a highly inflammatory disease with characteristic periodic fevers caused by the synchronous rupture of infected erythrocytes to release daughter parasites. Despite the importance of inflammation in the pathology and mortality induced by malaria, the parasite-derived factors inducing the inflammatory response are still not well characterized. Uric acid is emerging as a central inflammatory molecule in malaria. Not only is uric acid found in the precipitated form in infected erythrocytes, but high concentrations of hypoxanthine, a precursor for uric acid, also accumulate in infected erythrocytes. Both are released upon infected erythrocyte rupture into the circulation where hypoxanthine would be converted into uric acid and precipitated uric acid would encounter immune cells. Uric acid is an important contributor to inflammatory cytokine secretion, dendritic cell and T cell responses induced by Plasmodium, suggesting uric acid as a novel molecular target for anti-inflammatory therapies in malaria.

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Much of our current understanding about neurodegenerative diseases can be attributed to the study of inherited forms of these disorders. For example, mutations in the presenilin 1 and 2 genes have been linked to early onset familial forms of Alzheimer's disease (FAD). Using the Drosophila central nervous system as a model we have investigated the role of presenilin in one of the earliest cellular defects associated with Alzheimer's disease, intracellular calcium deregulation. We show that expression of either wild type or FAD-mutant presenilin in Drosophila CNS neurons has no impact on resting calcium levels but does give rise to deficits in intracellular calcium stores. Furthermore, we show that a loss-of-function mutation in calmodulin, a key regulator of intracellular calcium, can suppress presenilin-induced deficits in calcium stores. Our data support a model whereby presenilin plays a role in regulating intracellular calcium stores and demonstrate that Drosophila can be used to study the link between presenilin and calcium deregulation.