Reduced Peripheral PGE2 Biosynthesis in Plasmodium falciparum Malaria Occurs through Hemozoin-Induced Suppression of Blood Mononuclear Cell Cyclooxygenase-2 Gene Expression via an Interleukin-10-Independent Mechanism

Abstract

Molecular immunologic determinants of disease severity during Plasmodium falciparum malaria are largely undetermined. Our recent investigations showed that peripheral blood mononuclear cell (PBMC) cyclooxygenase-2 (COX-2) gene expression and plasma prostaglandin E(2) (PGE(2)) production are suppressed in children with falciparum malaria relative to healthy, malaria-exposed children with partial immunity. Furthermore, decreased COX-2/PGE(2) levels were significantly associated with increased plasma interleukin-10 (IL-10), an anti-inflammatory cytokine that inhibits the expression of COX-2 gene products. To determine the mechanism(s) responsible for COX-2-derived PGE(2) suppression, PBMCs were cultured from children with falciparum malaria. PGE(2) production was suppressed under baseline and COX-2-promoting conditions (stimulation with lipopolysaccharide [LPS] and interferon [IFN]-gamma) over prolonged periods, suggesting that an in vivo-derived product(s) was responsible for reduced PGE(2) biosynthesis. Ingestion of hemozoin (malarial pigment) by PBMC was investigated as a source of COX-2/PGE(2) suppression in PBMCs from healthy, malaria-naive adults. In addition, synthetically prepared hemozoin, beta-hematin, was used to investigate the effects of the core iron component of hemozoin, ferriprotoporphyrin-IX (FPIX). Physiologic concentrations of hemozoin or b-hematin suppressed LPS- and IFN-gamma-induced COX-2 mRNA in a time- and dose-dependent manner, resulting in decreased COX-2 protein and PGE(2) production. Suppression of COX-2/PGE(2) by hemozoin was not due to decreased cell viability as evidenced by examination of mitochondrial bioactivity. These data illustrate that ingestion of FPIX by blood mononuclear cells is responsible for suppression of COX-2/PGE(2). Although hemozoin induced overproduction of IL-10, neutralizing IL-10 antibodies failed to restore PGE(2) production. Thus, acquisition of hemozoin by blood mononuclear cells is responsible for suppression of PGE(2) in malaria through inhibition of de novo COX-2 transcripts via molecular mechanisms independent of increased IL-10 production.

Impaired Systemic Production of Prostaglandin E2in Children with Cerebral Malaria

“…Since we did not have access to cryopreserved PBMCs in the present study, we were unable to determine whether levels of COX-2 transcript and protein were suppressed in circulating blood mononuclear cells. Although the exact molecular mechanisms by which malaria suppresses COX-2 and PGs are presently unknown, we have recently found that ingestion of hemozoin (malarial pigment) and b-hematin (synthetic malarial pigment) by cultured monocytes decreases COX-2 gene expression and formation of PGE 2 [26]. Thus, we postulate that acquisition of parasitic products by circulating monocytes and tissue macrophages is directly responsible for the systemic reduction of PGs in children with CM reported in the present study.…”

Relationship between inflammatory mediator patterns and anemia in HIV‐1 positive and exposed children with Plasmodium falciparum malaria

“…Although studies by our group [4, 6, 10, 11, 49-51] and others [8, 41, 52-54] demonstrated that both malaria and HIV-1 cause significant changes in IM production, a comprehensive evaluation of the inflammatory milieu has not been reported in co-infected children. Technologies, such as the micro bead assays, which concomitantly measure an inclusive panel of IMs in the small volumes of blood available from anemic children, allowed us to determine the inflammatory profile in malaria-infected children with differing HIV-1 status.…”

Mechanisms of erythropoiesis inhibition by malarial pigment and malaria‐induced proinflammatory mediators in an in vitro model

“…Parasitized RBCs were then lysed and Pf Hz was isolated, dried and resuspended at 1.0 mg/mL as described previously [30]. Synthetic Hz, (β-hematin, sHz) was prepared from hemin chloride (Sigma, St Loius, MO) and also resuspended at 1.0 mg/mL per our previous methods [30].…”

“…Parasitized RBCs were then lysed and Pf Hz was isolated, dried and resuspended at 1.0 mg/mL as described previously [30]. Synthetic Hz, (β-hematin, sHz) was prepared from hemin chloride (Sigma, St Loius, MO) and also resuspended at 1.0 mg/mL per our previous methods [30]. Endotoxin levels in all Pf Hz and sHz preparations were determined to be <0.125 EU/mL (i.e., <0.025 ng/mL; Limulus amebocyte lysate test, BioWhittaker, Walkersville, MD), indicating that the preparations were free of endotoxins contamination.…”