New concepts in malaria pathogenesis: the role of the renin-angiotensin system

Malaria is a worldwide health problem leading the death of millions of people. The disease is induced by different species of protozoa parasites from the genus Plasmodium. In humans, Plasmodium falciparum is the most dangerous species responsible for severe disease. Despite all efforts to establish the pathogenesis of malaria, it is far from being fully understood. In addition, resistance to existing drugs has developed in several strains and the development of new effective compounds to fight these parasites is a major issue. Recent discoveries indicate the potential role of the renin-angiotensin system (RAS) in malaria infection. Angiotensin receptors have not been described in the parasite genome, however several reports in the literature suggest a direct effect of angiotensin-derived peptides on different aspects of the host-parasite interaction. The aim of this review is to highlight new findings on the involvement of the RAS in parasite development and in the regulation of the host immune response in an attempt to expand our knowledge of the pathogenesis of this disease

Kinins Released by Erythrocytic Stages of Plasmodium falciparum Enhance Adhesion of Infected Erythrocytes to Endothelial Cells and Increase Blood Brain Barrier Permeability via Activation of Bradykinin Receptors

Background:Plasmodium falciparum, the etiologic agent of malaria, is a major cause of infant death in Africa. Although research on the contact system has been revitalized by recent discoveries in the field of thrombosis, limited efforts were done to investigate the role of its proinflammatory arm, the kallikrein kinin system (KKS), in the pathogenesis of neglected parasitic diseases, such as malaria. Owing to the lack of animal models, the dynamics of central nervous system (CNS) pathology caused by the sequestration of erythrocytic stages of P. falciparum is not fully understood. Given the precedent that kinins destabilize the blood brain barrier (BBB) in ischemic stroke, here we sought to determine whether Plasmodium falciparum infected erythrocytes (Pf-iRBC) conditioned medium enhances parasite sequestration and impairs BBB integrity via activation of the kallikrein kinin system (KKS).Methods: Monolayers of human brain endothelial cell line (BMECs) are preincubated with the conditioned medium from Pf-iRBCs or RBCs (controls) in the presence or absence of HOE-140 or DALBK, antagonists of bradykinin receptor B2 (B2R) and bradykinin receptor B1 (B1R), respectively. Following washing, the treated monolayers are incubated with erythrocytes, infected or not with P. falciparum mature forms, to examine whether the above treatment (i) has impact on the adhesion of Pf-iRBC to BMEC monolayer, (ii) increases the macromolecular permeability of the tracer BSA-FITC, and (iii) modifies the staining pattern of junctional proteins (ZO-1 and β-catenin).Results: We found that kinins generated in the parasite conditioned medium, acting via bradykinin B2 and/or B1 receptors (i) enhanced Pf-iRBC adhesion to the endothelium monolayer and (ii) impaired the endothelial junctions formed by ZO-1 and β-catenin, consequently disrupting the integrity of the BBB.Conclusions: Our studies raise the possibility that therapeutic targeting of kinin forming enzymes and/or endothelial bradykinin receptors might reduce extent of Pf-iRBC sequestration and help to preserve BBB integrity in cerebral malaria (CM)

LPS Induces mTORC1 and mTORC2 Activation During Monocyte Adhesion

Monocyte adhesion is a crucial step in transmigration and can be induced by lipopolysaccharide (LPS). Here, we studied the role of mammalian target of rapamycin (mTOR) complexes, mTORC1 and mTORC2, and PKC in this process. We used THP-1 cells, a human monocytic cell line, to investigate monocyte adhesion under static and flow conditions. We observed that 1.0 μg/mL LPS increased PI3K/mTORC2 pathway and PKC activity after 1 h of incubation. WYE-354 10−6 M (mTORC2/mTORC1 inhibitor) and 10−6 M wortmannin avoided monocyte adhesion in culture plates. In addition, WYE also blocked LPS-induced CD11a expression. Interestingly, rapamycin and WYE-354 blocked both LPS-induced monocyte adhesion in a cell monolayer and actin cytoskeleton rearrangement, confirming mTORC1 involvement in this process. Once activated, PKC activates mTORC1/S6K pathway in a similar effect observed to LPS. Activation of the mTORC1/S6K pathway was attenuated by 10−6 M U0126, an MEK/ERK inhibitor, and 10−6 M calphostin C, a PKC inhibitor, indicating that the MEK/ERK/TSC2 axis acts as a mediator. In agreement, 80 nM PMA (a PKC activator) mimicked the effect of LPS on the activation of the MEK/ERK/TSC2/mTORC1/S6K pathway, monocyte adhesion to ECV cells and actin cytoskeleton rearrangement. Our findings show that LPS induces activation of mTOR complexes. This signaling pathway led to integrin expression and cytoskeleton rearrangement resulting in monocyte adhesion. These results describe a new molecular mechanism involved in monocyte adhesion in immune-based diseases

Impairment of the Plasmodium falciparum Erythrocytic Cycle Induced by Angiotensin Peptides

Plasmodium falciparum causes the most serious complications of malaria and is a public health problem worldwide with over 2 million deaths each year. The erythrocyte invasion mechanisms by Plasmodium sp. have been well described, however the physiological aspects involving host components in this process are still poorly understood. Here, we provide evidence for the role of renin-angiotensin system (RAS) components in reducing erythrocyte invasion by P. falciparum. Angiotensin II (Ang II) reduced erythrocyte invasion in an enriched schizont culture of P. falciparum in a dose-dependent manner. Using mass spectroscopy, we showed that Ang II was metabolized by erythrocytes to Ang IV and Ang-(1–7). Parasite infection decreased Ang-(1–7) and completely abolished Ang IV formation. Similar to Ang II, Ang-(1–7) decreased the level of infection in an A779 (specific antagonist of Ang-(1–7) receptor, MAS)-sensitive manner. 10−7 M PD123319, an AT2 receptor antagonist, partially reversed the effects of Ang-(1–7) and Ang II. However, 10−6 M losartan, an antagonist of the AT1 receptor, had no effect. Gs protein is a crucial player in the Plasmodium falciparum blood cycle and angiotensin peptides can modulate protein kinase A (PKA) activity; 10−8 M Ang II or 10−8 M Ang-(1–7) inhibited this activity in erythrocytes by 60% and this effect was reversed by 10−7 M A779. 10−6 M dibutyryl-cAMP increased the level of infection and 10−7 M PKA inhibitor decreased the level of infection by 30%. These results indicate that the effect of Ang-(1–7) on P. falciparum blood stage involves a MAS-mediated PKA inhibition. Our results indicate a crucial role for Ang II conversion into Ang-(1–7) in controlling the erythrocytic cycle of the malaria parasite, adding new functions to peptides initially described to be involved in the regulation of vascular tonus

Impairment of the Plasmodium falciparum Erythrocytic Cycle Induced by Angiotensin Peptides

Plasmodium falciparum causes the most serious complications of malaria and is a public health problem worldwide with over 2 million deaths each year. The erythrocyte invasion mechanisms by Plasmodium sp. have been well described, however the physiological aspects involving host components in this process are still poorly understood. Here, we provide evidence for the role of renin-angiotensin system (RAS) components in reducing erythrocyte invasion by P. falciparum. Angiotensin II (Ang II) reduced erythrocyte invasion in an enriched schizont culture of P. falciparum in a dose-dependent manner. Using mass spectroscopy, we showed that Ang II was metabolized by erythrocytes to Ang IV and Ang-(1–7). Parasite infection decreased Ang-(1–7) and completely abolished Ang IV formation. Similar to Ang II, Ang-(1–7) decreased the level of infection in an A779 (specific antagonist of Ang-(1–7) receptor, MAS)-sensitive manner. 10−7 M PD123319, an AT2 receptor antagonist, partially reversed the effects of Ang-(1–7) and Ang II. However, 10−6 M losartan, an antagonist of the AT1 receptor, had no effect. Gs protein is a crucial player in the Plasmodium falciparum blood cycle and angiotensin peptides can modulate protein kinase A (PKA) activity; 10−8 M Ang II or 10−8 M Ang-(1–7) inhibited this activity in erythrocytes by 60% and this effect was reversed by 10−7 M A779. 10−6 M dibutyryl-cAMP increased the level of infection and 10−7 M PKA inhibitor decreased the level of infection by 30%. These results indicate that the effect of Ang-(1–7) on P. falciparum blood stage involves a MAS-mediated PKA inhibition. Our results indicate a crucial role for Ang II conversion into Ang-(1–7) in controlling the erythrocytic cycle of the malaria parasite, adding new functions to peptides initially described to be involved in the regulation of vascular tonus

High Doses of Essential Oil of Croton Zehntneri Induces Renal Tubular Damage

The essential oil of Croton zehntneri (EOCZ) and its major compounds are known to have several biological activities. However, some evidence shows potential toxic effects of high doses of EOCZ (>300 mg/kg) in amphibian and human kidneys. The aim of the present work was to investigate the effects on renal function of EOCZ at 300 mg/kg/day in healthy Swiss mice and a subclinical acute kidney injury (subAKI) animal model, which presents tubule-interstitial injury (TII). Four experimental groups were generated: (1) CONT group (control); (2) EOCZ, mice treated with EOCZ; (3) subAKI; (4) subAKI+EOCZ, subAKI treated simultaneously with EOCZ. EOCZ treatment induced TII measured by increases in (1) proteinuria; (2) cortical tubule-interstitial space; (3) macrophage infiltration; (4) collagen deposition. A decrease in tubular sodium reabsorption was also observed. These results were similar and nonadditive to those observed in the subAKI group. These data suggest that treatment with EOCZ at higher concentrations induces TII in mice, which could be mediated by protein overload in the proximal tubule

Mice Rescued from Severe Malaria Are Protected against Renal Injury during a Second Kidney Insult

<div><p>Malaria is a worldwide disease that leads to 1 million deaths per year. <i>Plasmodium falciparum</i> is the species responsible for the most severe form of malaria leading to different complications. Beyond the development of cerebral malaria, impairment of renal function is a mortality indicator in infected patients. Treatment with antimalarial drugs can increase survival, however the long-term effects of malaria on renal disease, even after treatment with antimalarials, are unknown. The aim of this study was to evaluate the effect of antimalarial drug treatment on renal function in a murine model of severe malaria and then evaluate kidney susceptibility to a second renal insult. Initially, mice infected with <i>Plasmodium berghei</i> ANKA achieved 20% parasitemia on day 5 post infection, which was completely abolished after treatment with 25 mg/kg artesunate and 40 mg/kg mefloquine. The treatment also decreased plasma creatinine levels by 43% and partially reversed the reduction in the glomerular filtration rate induced by infection. The urinary protein/creatinine ratio, collagen deposition, and size of the interstitial space decreased by 75%, 40%, and 20%, respectively, with drugs compared with untreated infected animals. In infected-treated mice that underwent a second renal insult, the plasma creatinine level decreased by 60% and the glomerular filtration rate increased compared with infected animals treated only with antimalarials. The number of glomerular cells, collagen deposition and the size of the interstitial space decreased by 20%, 39.4%, and 41.3%, respectively, in the infected group that underwent a second renal insult compared with the infected-treated groups. These functional and structural data show that renal injury observed in a murine model of severe malaria is partially reversed after antimalarial drug treatment, making the kidney less susceptible to a second renal insult.</p></div

Glomerular cell number decreases in mice subjected to a second kidney insult.

<p>Animals were euthanized on day 21 post infection (p.i.), perfused, and the kidneys were collected for histologic analysis. The number of glomerular cells in the renal cortex was visualized using periodic acid−Schiff. Representative photomicrographs of (<b>A</b>) control_21d, (<b>B</b>) control+BSA _21d, (<b>C</b>) control+treated+BSA _21d, (<b>D</b>) infected+treated _21d, and (<b>E</b>) infected+treated+BSA _21d (<i>n</i> = 6 per group). Bar = 40 µm. The number of glomerular cells is quantified in (<b>F</b>). The results are expressed as means ± standard error. *Statistically significant compared with control_21d. #Statistically significant compared with infected+treated _21d (<i>P</i><0.05).</p

Effect of antimalarial treatment on malaria-induced renal damage.

<p>Animals were euthanized at day 5 or 21 post infection and plasma and urine samples were collected for analysis of renal function. Analysis of (<b>A</b>) urinary flow, (<b>B</b>) serum creatinine, (<b>C</b>) blood urea nitrogen (BUN), (D) creatinine clearance (CCr), (<b>E</b>) BUN/serum creatinine ratio, and (<b>F</b>) urinary protein/creatinine (UPC) ratio in different experimental groups as depicted in the figure. *Statistically significant compared with control_5d or control+treated_21d. #Statistically significant compared with control_5d or infected_5d (<i>P</i><0.05).</p

Renal collagen deposition decreases in mice subjected to a second kidney insult.

<p>Animals were euthanized on day 21 post infection (p.i.), perfused, and the kidneys were collected for histologic analysis. Collagen deposition in the renal cortex was visualized using Picrosirius Red. Representative photomicrographs of (<b>A</b>) control_21d, (<b>B</b>) control+BSA_21d, (<b>C</b>) control+treated+BSA_21d, (<b>D</b>) infected+treated_21d, and (<b>E</b>) infected+treated+BSA_21d (<i>n</i> = 6 per group). Bar = 20 µm. Collagen deposition is quantified in (<b>F</b>). Values are expressed as a percentage of collagen deposition per area (means ± standard error). *Statistically significant compared with control_21d. #Statistically significant compared with infected+treated _21d (<i>P</i><0.05).</p