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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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Identification of a soluble factor that induces TNF secretion by DC.(A) Ultraviolet chromatogram of the non-hydrophobic fraction from the conditioned medium of P. yoelii infected erythrocytes (red) compared to the non-hydrophobic fraction of the conditioned medium of uninfected erythrocytes (black) from a sizing HPLC column. Arrows indicate the position of molecular weight standards. Arrowheads point to three peaks collected for mass spectrometry analysis. (B) Total ion current plot from GC-EI-MS analysis of the TMS-derivatized fraction 1 (red) from A compared to the reagent blank (black). (C) Top, full EI-MS of the 13.22 min fraction in A. Bottom, matching mass spectrum from the NIST database identifying hypoxanthine as high confidence match.
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ppat-1000013-g002: Identification of a soluble factor that induces TNF secretion by DC.(A) Ultraviolet chromatogram of the non-hydrophobic fraction from the conditioned medium of P. yoelii infected erythrocytes (red) compared to the non-hydrophobic fraction of the conditioned medium of uninfected erythrocytes (black) from a sizing HPLC column. Arrows indicate the position of molecular weight standards. Arrowheads point to three peaks collected for mass spectrometry analysis. (B) Total ion current plot from GC-EI-MS analysis of the TMS-derivatized fraction 1 (red) from A compared to the reagent blank (black). (C) Top, full EI-MS of the 13.22 min fraction in A. Bottom, matching mass spectrum from the NIST database identifying hypoxanthine as high confidence match.

Mentions: The non-hydrophobic fraction of the conditioned medium from control and P. yoelii-infected erythrocytes was separated further by HPLC on a sizing column (Superdex 200 HR 10/30) monitored with a diode array ultraviolet spectrum (UV) detector. Several peaks of low molecular weight (<250 Da) were only found in the conditioned medium of P. yoelii-infected erythrocytes, but not in the conditioned medium of uninfected erythrocytes (Fig. 2A). Since common desalting methods exploit hydrophobicity and size to achieve separation, we were not able to isolate the low molecular weight fractions containing non-hydrophobic molecules from the HPLC buffer salts. The high concentrations of salts were toxic to DCs prohibiting the direct testing of the fractions for their activity on DCs. Thus, we identified the molecular components found in these peaks and tested their activity on DCs. Three low molecular weight peaks found only in the conditioned medium of P. yoelii-infected erythrocytes were isolated, subjected to trimethylsilyl (TMS) derivitization and analyzed by gas chromatography (GC) coupled with electron impact mass spectrometry (EI-MS) as previously described [8]. We detected a single GC peak at 13.22 min for peak 1 (Fig. 2B). A search of the National Institute of Standards and Technology (NIST) database of EI mass spectra returned a highly probably match with tetra-TMS hypoxanthine (Fig. 2C). The same method identified urea and xanthine as components of peaks 2 and 3 (Fig. S1). These three compounds are in the uric acid metabolic pathway [9]. Uric acid is a well-characterized pro-inflammatory molecule that in its crystallized form induces the release of inflammatory mediators [10],[11]. In addition, soluble uric acid can stimulate the production of inflammatory mediators from different cell types [12]–[14].


Plasmodium-induced inflammation by uric acid.

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

Identification of a soluble factor that induces TNF secretion by DC.(A) Ultraviolet chromatogram of the non-hydrophobic fraction from the conditioned medium of P. yoelii infected erythrocytes (red) compared to the non-hydrophobic fraction of the conditioned medium of uninfected erythrocytes (black) from a sizing HPLC column. Arrows indicate the position of molecular weight standards. Arrowheads point to three peaks collected for mass spectrometry analysis. (B) Total ion current plot from GC-EI-MS analysis of the TMS-derivatized fraction 1 (red) from A compared to the reagent blank (black). (C) Top, full EI-MS of the 13.22 min fraction in A. Bottom, matching mass spectrum from the NIST database identifying hypoxanthine as high confidence match.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2267007&req=5

ppat-1000013-g002: Identification of a soluble factor that induces TNF secretion by DC.(A) Ultraviolet chromatogram of the non-hydrophobic fraction from the conditioned medium of P. yoelii infected erythrocytes (red) compared to the non-hydrophobic fraction of the conditioned medium of uninfected erythrocytes (black) from a sizing HPLC column. Arrows indicate the position of molecular weight standards. Arrowheads point to three peaks collected for mass spectrometry analysis. (B) Total ion current plot from GC-EI-MS analysis of the TMS-derivatized fraction 1 (red) from A compared to the reagent blank (black). (C) Top, full EI-MS of the 13.22 min fraction in A. Bottom, matching mass spectrum from the NIST database identifying hypoxanthine as high confidence match.
Mentions: The non-hydrophobic fraction of the conditioned medium from control and P. yoelii-infected erythrocytes was separated further by HPLC on a sizing column (Superdex 200 HR 10/30) monitored with a diode array ultraviolet spectrum (UV) detector. Several peaks of low molecular weight (<250 Da) were only found in the conditioned medium of P. yoelii-infected erythrocytes, but not in the conditioned medium of uninfected erythrocytes (Fig. 2A). Since common desalting methods exploit hydrophobicity and size to achieve separation, we were not able to isolate the low molecular weight fractions containing non-hydrophobic molecules from the HPLC buffer salts. The high concentrations of salts were toxic to DCs prohibiting the direct testing of the fractions for their activity on DCs. Thus, we identified the molecular components found in these peaks and tested their activity on DCs. Three low molecular weight peaks found only in the conditioned medium of P. yoelii-infected erythrocytes were isolated, subjected to trimethylsilyl (TMS) derivitization and analyzed by gas chromatography (GC) coupled with electron impact mass spectrometry (EI-MS) as previously described [8]. We detected a single GC peak at 13.22 min for peak 1 (Fig. 2B). A search of the National Institute of Standards and Technology (NIST) database of EI mass spectra returned a highly probably match with tetra-TMS hypoxanthine (Fig. 2C). The same method identified urea and xanthine as components of peaks 2 and 3 (Fig. S1). These three compounds are in the uric acid metabolic pathway [9]. Uric acid is a well-characterized pro-inflammatory molecule that in its crystallized form induces the release of inflammatory mediators [10],[11]. In addition, soluble uric acid can stimulate the production of inflammatory mediators from different cell types [12]–[14].

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