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Plasmodium-induced inflammation by uric acid.

Orengo JM, Evans JE, Bettiol E, Leliwa-Sytek A, Day K, Rodriguez A - PLoS Pathog. (2008)

Bottom Line: Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells.Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF.Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Parasitology, New York University School of Medicine, New York, New York, USA.

ABSTRACT
Infection of erythrocytes with the Plasmodium parasite causes the pathologies associated with malaria, which result in at least one million deaths annually. The rupture of infected erythrocytes triggers an inflammatory response, which is induced by parasite-derived factors that still are not fully characterized. Induced secretion of inflammatory cytokines by these factors is considered a major cause of malaria pathogenesis. In particular, the inflammatory cytokine tumor necrosis factor (TNF) is thought to mediate most of the life-threatening pathologies of the disease. Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells. We found that erythrocytes infected by Plasmodium accumulate high concentrations of hypoxanthine and xanthine. Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF. Since uric acid is considered a "danger signal" released by dying cells to alert the immune system, Plasmodium appears to have co-evolved to exploit this warning system. Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

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Plasmodium infected erythrocytes accumulate hypoxanthine/xanthine.Hypoxanthine induces DCs to secrete TNF in the presence of serum. The concentration of hypoxanthine/xanthine was determined in the soluble fraction of schizont lysates of P. yoelii (A), P. berghei (B) and P. falciparum (C). Lysates of uninfected murine and human erythrocytes were used as controls. (D) Ultraviolet spectrum profiles of HPLC fractionation of the soluble fraction of lysates of P. yoelii schizonts (blue) and uninfected erythrocytes (green). Arrows indicate the positions of hypoxanthine and xanthine when run independently. (E, F) DCs were incubated in medium supplemented or not with 10% fetal bovine (FBS; E) or human (HS; F) serum in the presence or absence of hypoxanthine or LPS for one hour. The incubation medium was removed, cells were washed, and medium supplemented with either 10% FBS or 10% HS was added. After 24 h, incubation media were collected and TNF concentrations were determined by ELISA. Data represent the average of triplicated samples with standard deviations. **P<0.01.
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ppat-1000013-g003: Plasmodium infected erythrocytes accumulate hypoxanthine/xanthine.Hypoxanthine induces DCs to secrete TNF in the presence of serum. The concentration of hypoxanthine/xanthine was determined in the soluble fraction of schizont lysates of P. yoelii (A), P. berghei (B) and P. falciparum (C). Lysates of uninfected murine and human erythrocytes were used as controls. (D) Ultraviolet spectrum profiles of HPLC fractionation of the soluble fraction of lysates of P. yoelii schizonts (blue) and uninfected erythrocytes (green). Arrows indicate the positions of hypoxanthine and xanthine when run independently. (E, F) DCs were incubated in medium supplemented or not with 10% fetal bovine (FBS; E) or human (HS; F) serum in the presence or absence of hypoxanthine or LPS for one hour. The incubation medium was removed, cells were washed, and medium supplemented with either 10% FBS or 10% HS was added. After 24 h, incubation media were collected and TNF concentrations were determined by ELISA. Data represent the average of triplicated samples with standard deviations. **P<0.01.

Mentions: To confirm the MS identifications, we first determined whether hypoxanthine and xanthine are accumulated in P. yoelii conditioned medium (not shown) and in infected erythrocytes. We used a quantification method based on the enzyme xanthine oxidoreductase (XO), which specifically degrades hypoxanthine and xanthine to uric acid while releasing reactive oxygen species (ROS). We found that the concentration of xanthine/hypoxanthine in the soluble fraction of lysates from late stage P. yoelii-infected erythrocytes (schizonts) was very high compared to control uninfected erythrocytes where xanthine/hypoxanthine was not detected (Fig. 3A). Similar results were found for another rodent parasite, P. berghei, and for the human parasite P. falciparum (Fig. 3B,C). We also found that when control, human, uninfected erythrocytes were cultured in vitro in the presence of hypoxanthine, they too accumulated hypoxanthine, although at lower concentrations compared to P. falciparum infected erythrocytes. This is likely because of the excess hypoxanthine (500 µM) used in the parasite culture medium. Using HPLC sizing analysis of the soluble fraction of a lysate of P. yoelii schizonts, we also found two peaks in the positions corresponding to hypoxanthine and xanthine (Fig. 3D).


Plasmodium-induced inflammation by uric acid.

Orengo JM, Evans JE, Bettiol E, Leliwa-Sytek A, Day K, Rodriguez A - PLoS Pathog. (2008)

Plasmodium infected erythrocytes accumulate hypoxanthine/xanthine.Hypoxanthine induces DCs to secrete TNF in the presence of serum. The concentration of hypoxanthine/xanthine was determined in the soluble fraction of schizont lysates of P. yoelii (A), P. berghei (B) and P. falciparum (C). Lysates of uninfected murine and human erythrocytes were used as controls. (D) Ultraviolet spectrum profiles of HPLC fractionation of the soluble fraction of lysates of P. yoelii schizonts (blue) and uninfected erythrocytes (green). Arrows indicate the positions of hypoxanthine and xanthine when run independently. (E, F) DCs were incubated in medium supplemented or not with 10% fetal bovine (FBS; E) or human (HS; F) serum in the presence or absence of hypoxanthine or LPS for one hour. The incubation medium was removed, cells were washed, and medium supplemented with either 10% FBS or 10% HS was added. After 24 h, incubation media were collected and TNF concentrations were determined by ELISA. Data represent the average of triplicated samples with standard deviations. **P<0.01.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2267007&req=5

ppat-1000013-g003: Plasmodium infected erythrocytes accumulate hypoxanthine/xanthine.Hypoxanthine induces DCs to secrete TNF in the presence of serum. The concentration of hypoxanthine/xanthine was determined in the soluble fraction of schizont lysates of P. yoelii (A), P. berghei (B) and P. falciparum (C). Lysates of uninfected murine and human erythrocytes were used as controls. (D) Ultraviolet spectrum profiles of HPLC fractionation of the soluble fraction of lysates of P. yoelii schizonts (blue) and uninfected erythrocytes (green). Arrows indicate the positions of hypoxanthine and xanthine when run independently. (E, F) DCs were incubated in medium supplemented or not with 10% fetal bovine (FBS; E) or human (HS; F) serum in the presence or absence of hypoxanthine or LPS for one hour. The incubation medium was removed, cells were washed, and medium supplemented with either 10% FBS or 10% HS was added. After 24 h, incubation media were collected and TNF concentrations were determined by ELISA. Data represent the average of triplicated samples with standard deviations. **P<0.01.
Mentions: To confirm the MS identifications, we first determined whether hypoxanthine and xanthine are accumulated in P. yoelii conditioned medium (not shown) and in infected erythrocytes. We used a quantification method based on the enzyme xanthine oxidoreductase (XO), which specifically degrades hypoxanthine and xanthine to uric acid while releasing reactive oxygen species (ROS). We found that the concentration of xanthine/hypoxanthine in the soluble fraction of lysates from late stage P. yoelii-infected erythrocytes (schizonts) was very high compared to control uninfected erythrocytes where xanthine/hypoxanthine was not detected (Fig. 3A). Similar results were found for another rodent parasite, P. berghei, and for the human parasite P. falciparum (Fig. 3B,C). We also found that when control, human, uninfected erythrocytes were cultured in vitro in the presence of hypoxanthine, they too accumulated hypoxanthine, although at lower concentrations compared to P. falciparum infected erythrocytes. This is likely because of the excess hypoxanthine (500 µM) used in the parasite culture medium. Using HPLC sizing analysis of the soluble fraction of a lysate of P. yoelii schizonts, we also found two peaks in the positions corresponding to hypoxanthine and xanthine (Fig. 3D).

Bottom Line: Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells.Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF.Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Parasitology, New York University School of Medicine, New York, New York, USA.

ABSTRACT
Infection of erythrocytes with the Plasmodium parasite causes the pathologies associated with malaria, which result in at least one million deaths annually. The rupture of infected erythrocytes triggers an inflammatory response, which is induced by parasite-derived factors that still are not fully characterized. Induced secretion of inflammatory cytokines by these factors is considered a major cause of malaria pathogenesis. In particular, the inflammatory cytokine tumor necrosis factor (TNF) is thought to mediate most of the life-threatening pathologies of the disease. Here we describe the molecular characterization of a novel pathway that results in the secretion of TNF by host cells. We found that erythrocytes infected by Plasmodium accumulate high concentrations of hypoxanthine and xanthine. Degradation of Plasmodium-derived hypoxanthine/xanthine results in the formation of uric acid, which triggers the secretion of TNF. Since uric acid is considered a "danger signal" released by dying cells to alert the immune system, Plasmodium appears to have co-evolved to exploit this warning system. Identifying the mechanisms used by the parasite to induce the host inflammatory response is essential to develop urgently needed therapies against this disease.

Show MeSH
Related in: MedlinePlus