Phagocytosis of hemozoin enhances matrix metalloproteinase-9 activity and TNF-alpha production in human monocytes: role of matrix metalloproteinases in the pathogenesis of falciparum malaria

The roles of COX-2 in protozoan infection

Protozoan diseases cause great harm in animal husbandry and require human-provided medical treatment. Protozoan infection can induce changes in cyclooxygenase-2 (COX-2) expression. The role played by COX-2 in the response to protozoan infection is complex. COX-2 induces and regulates inflammation by promoting the synthesis of different prostaglandins (PGs), which exhibit a variety of biological activities and participate in pathophysiological processes in the body in a variety of ways. This review explains the roles played by COX-2 in protozoan infection and analyzes the effects of COX-2-related drugs in protozoan diseases.

Myeloperoxidase and Other Markers of Neutrophil Activation Associate With Malaria and Malaria/HIV Coinfection in the Human Placenta

Introduction

Placental malaria (PM) is characterized by accumulation of inflammatory leukocytes in the placenta, leading to poor pregnancy outcomes. Understanding of the underlying mechanisms remains incomplete. Neutrophils respond to malaria parasites by phagocytosis, generation of oxidants, and externalization of Neutrophil Extracellular Traps (NETs). NETs drive inflammation in malaria but evidence of NETosis in PM has not been reported. Neutrophil activity in the placenta has not been directly investigated in the context of PM and PM/HIV-co-infection.

Methods

Using peripheral and placental plasma samples and placental tissue collected from Kenyan women at risk for malaria and HIV infections, we assessed granulocyte levels across all gravidities and markers of neutrophil activation, including NET formation, in primi- and secundigravid women, by ELISA, western blot, immunohistochemistry and immunofluorescence.

Results

Reduced peripheral blood granulocyte numbers are observed with PM and PM/HIV co-infection in association with increasing parasite density and placental leukocyte hemozoin accumulation. In contrast, placental granulocyte levels are unchanged across infection groups, resulting in enhanced placental: peripheral count ratios with PM. Within individuals, PM- women have reduced granulocyte counts in placental relative to peripheral blood; in contrast, PM stabilizes these relative counts, with HIV coinfection tending to elevate placental counts relative to the periphery. In placental blood, indicators of neutrophil activation, myeloperoxidase (MPO) and proteinase 3 (PRTN3), are significantly elevated with PM and, more profoundly, with PM/HIV co-infection, in association with placental parasite density and hemozoin-bearing leukocyte accumulation. Another neutrophil marker, matrix metalloproteinase (MMP9), together with MPO and PRTN3, is elevated with self-reported fever. None of these factors, including the neutrophil chemoattractant, CXCL8, differs in relation to infant birth weight or gestational age. CXCL8 and MPO levels in the peripheral blood do not differ with infection status nor associate with birth outcomes. Indicators of NETosis in the placental plasma do not vary with infection, and while structures consistent with NETs are observed in placental tissue, the results do not support an association with PM.

Conclusions

Granulocyte levels are differentially regulated in the peripheral and placental blood in the presence and absence of PM. PM, both with and without pre-existing HIV infection, enhances neutrophil activation in the placenta. The impact of local neutrophil activation on placental function and maternal and fetal health remains unclear. Additional investigations exploring how neutrophil activation and NETosis participate in the pathogenesis of malaria in pregnant women are needed.

Proteomic identification of the contents of small extracellular vesicles from in vivo Plasmodium yoelii infection

Small extracellular vesicles, including exosomes, are formed by the endocytic pathway and contain genetic and protein material which reflect the contents of their cells of origin. These contents have a role in vesicle-mediated information transfer, as well as physiological and pathological functions. Thus, these vesicles are of great interest as therapeutic targets, or as vehicles for immunomodulatory control. In Plasmodium spp. infections, vesicles derived from the parasite or parasite-infected cells have been shown to induce the expression of pro-inflammatory elements, which have been correlated with manifestations of clinical disease. Herein, we characterised the protein cargo of naturally occurring sEVs in the plasma of P. yoelii-infected mice. After in vivo infections, extracellular vesicles in the size range of exosomes were collected by sequential centrifugation/ultracentrifugation followed by isopycnic gradient separation. Analysis of the vesicles was performed by transmission electron microscopy, dynamic light scattering, SDS-PAGE and flow cytometry. LC-MS analysis followed by bioinformatics analysis predicted parasite protein cargo associated with exosomes. Within these small extracellular vesicles, we identified proteins of interest as vaccine candidates, uncharacterized proteins which may be targets of T cell immunoreactivity, and proteins involved in metabolic processes, regulation, homeostasis and immunity. Importantly, the small extracellular vesicles studied in our work were obtained from in vivo infection rather than from the supernatant of in vitro cultures. These findings add to the growing interest in parasite small extracellular vesicles, further our understanding of the interactions between host and parasite, and identify novel proteins which may represent potential targets for vaccination against malaria.

Molecular docking study of flavonoid compounds for possible matrix metalloproteinase-13 inhibition

OBJECTIVES

Matrix metalloproteinase-13 (MMP-13) has been reported to be involved in different biological processes such as degradation of extracellular matrix proteins, activating or degrading some significant regulatory proteins, wound healing, tissue remodeling, cartilage degradation, bone development, bone mineralization, ossification, cell migration, and tumor cell invasion. Further, MMP-13 participates in many oral diseases such as tooth decay, gingivitis, and degradation of enamel and tissue around the implant. In addition, inhibition of MMP-13 has shown therapeutic properties for Alzheimer's disease (AD). We performed molecular docking to assess the binding affinity of 29 flavonoid compounds with the MMP-13. Additionally, pharmacokinetic and toxicity characteristics of the top-ranked flavonoids were studied. The current study also intended to identify the most important amino acids involved in the inhibition of MMP-13 based on topological feature (degree) in the ligand-amino acid network for MMP-13.

METHODS

Molecular docking and network analysis were studied using AutoDock and Cytoscape software, respectively. Pharmacokinetic and toxicity characteristics of compounds were predicted using bioinformatics web tools.

RESULTS

The results revealed that nine of the studied flavonoids had considerable estimated free energy of binding and inhibition constant: Rutin, nicotiflorin, orientin, vitexin, apigenin-7-glucoside, quercitrin, isoquercitrin, quercitrin-3-rhamnoside, and vicenin-2. Proline-242 was found to be the most important amino acid inhibiting the enzyme.

CONCLUSIONS

The results of the current study may be helpful in the prevention and therapeutic procedures of many disorders such as cancer, tooth caries, and AD. Nevertheless, validation tests are required in the future.

Hemozoin in Malarial Complications: More Questions Than Answers

Plasmodium parasites contain various virulence factors that modulate the host immune response. Malarial pigment, or hemozoin (Hz), is an undegradable crystalline product of the hemoglobin degradation pathway in the parasite and possesses immunomodulatory properties. An association has been found between Hz accumulation and severe malaria, suggesting that the effects of Hz on the host immune response may contribute to the development of malarial complications. Although the immunomodulatory roles of Hz have been widely investigated, many conflicting data exist, likely due to the variability between experimental set-ups and technical limitations of Hz generation and isolation methods. Here, we critically assess the potential immunomodulatory effects of Hz, its role in malarial complications, and its potential effects after parasite clearance.

Oral administration of Coenzyme Q10 protects mice against oxidative stress and neuro-inflammation during experimental cerebral malaria

In animal model of experimental cerebral malaria (ECM), the genesis of neuropathology is associated with oxidative stress and inflammatory mediators. There is limited progress in the development of new approaches to the treatment of cerebral malaria. Here, we tested whether oral supplementation of Coenzyme Q₁₀ (CoQ₁₀) would offer protection against oxidative stress and brain associated inflammation following Plasmodium berghei ANKA (PbA) infection in C57BL/6 J mouse model. For this purpose, one group of C57BL/6 mice was used as control; second group of mice were orally supplemented with 200 mg/kg CoQ₁₀ and then infected with PbA and the third group was PbA infected alone. Clinical, biochemical, immunoblot and immunological features of ECM was monitored. We observed that oral administration of CoQ₁₀ for 1 month and after PbA infection was able to improve survival, significantly reduced oedema, TNF-α and MIP-1β gene expression in brain samples in PbA infected mice. The result also shows the ability of CoQ₁₀ to reduce cholesterol and triglycerides lipids, levels of matrix metalloproteinases-9, angiopoietin-2 and angiopoietin-1 in the brain. In addition, CoQ₁₀ was very effective in decreasing NF-κB phosphorylation. Furthermore, CoQ₁₀ supplementation abrogated Malondialdehyde, and 8-OHDG and restored cellular glutathione. These results constitute the first demonstration that oral supplementation of CoQ₁₀ can protect mice against PbA induced oxidative stress and neuro-inflammation usually observed in ECM. Thus, the need to study CoQ₁₀ as a candidate of antioxidant and immunomodulatory molecule in ECM and testing it in clinical studies either alone or in combination with antimalaria regimens to provide insight into a potential translatable therapy.

Genesis of placental sequestration in malaria and possible targets for drugs for placental malaria

Malaria during pregnancy results in intrauterine growth restriction, fetal anemia, and infant mortality. Women are more susceptible to malaria during pregnancy due to malaria‐induced inflammation and the sequestration of infected red blood cells in the placenta, which bind to the chondroitin sulfate portion of syndecan‐1 on the syncytiotrophoblast and in the intervillous space. Syndecan‐1 is a dimeric proteoglycan with an extracellular ectodomain that is cleaved from the transmembrane domain (referred to as “shedding”) by matrix metalloproteinases (MMPs), likely the secreted MMP‐9. The ectodomain includes four binding sites for chondroitin sulfate, which are proximal to the transmembrane domain, and six distal binding sites primarily for heparan sulfate. This “shedding” of syndecan‐1 is inhibited by the presence of the heparan sulfate chains, which can be removed by heparanase. The intervillous space contains fibrin strands and syndecan‐1 ectodomains free of heparan sulfate. The following is proposed as the sequence of events that leads to and is primarily responsible for sequestration in the intervillous space of the placenta. Inflammation associated with malaria triggers increased heparanase activity that degrades the heparan sulfate on the membrane‐bound syndecan‐1. Inflammation also upregulates MMP‐9 and the removal of heparan sulfate gives MMP‐9 access to cleave syndecan‐1, thereby releasing dimeric syndecan‐1 ectodomains with at least four chondroitin sulfate chains attached. These multivalent ectodomains bind infected RBCs together leading to their aggregation and entrapment in intervillous fibrin. This mechanism suggests possible new targets for anti‐placental malaria drugs such as the inhibition of MMP‐9. Doxycycline is an antimalarial drug which inhibits MMP‐9.

Monocyte phagocytosis of malaria β-haematin in the presence of artemisinin, amodiaquine, chloroquine, doxycycline, primaquine, pyrimethamine and quinine

The intraerythrocytic malaria parasite digests haemoglobin to provide amino acids for metabolism and releases toxic haem that is sequestered into haemozoin, a non-toxic, insoluble, crystalline pigment. Following erythrocyte rupture, haemozoin is released into circulation and phagocytosed by monocytes. Phagocytosed haemozoin and antimalarial drugs have both been reported to modulate monocyte functions. This study determined the effects of therapeutic concentrations of seven antimalarial drugs; amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine and quinine, on the phagocytosis of β-haematin (synthetic haemozoin) by two monocytic cell lines, J774A.1 and U937, and human peripheral blood mononuclear cells. A novel spectrophotometric method based on the absorbance (O.D 400 nm) of alkali/SDS treated monocytes containing β-haematin was developed to complement counting phagocytosis with microscopy. The method has potential use for the large scale screening of monocyte phagocytic activity. Artemisinin, quinine, primaquine and pyrimethamine activated β-haematin phagocytosis by 12% or more, whereas amodiaquine, chloroquine and doxycyline inhibited β-haematin phagocytosis. In contrast, antimalarial drugs had minimal inhibitory effects on the phagocytosis of latex beads with only quinine resulting in more than 20% inhibition. Antimalarial drugs appear to alter monocyte phagocytic activity which has implications for the treatment, pathogenicity and adjunct therapies for malaria.

The yin/yang of inflammatory status: Blood-brain barrier regulation during sleep

Sleep loss induces a low-grade inflammatory status characterized by a subtle but sustained increase of pro-inflammatory mediators, which are key regulators of blood-brain barrier function. To investigate the influence of inflammatory status on blood-brain barrier dysfunction induced by sleep restriction we performed an experiment using two strains of mice with different immunological backgrounds, C57BL/6 mice that have a predominant pro-inflammatory response and BALB/c mice that have a predominant anti-inflammatory response. Mice were sleep-restricted during 10 days using the flowerpot technique during 20 h per day with 4 h of daily sleep opportunity. The systemic inflammatory status, blood-brain barrier permeability, and the hippocampal expression of neuroinflammatory markers were characterized at the 10th day. Serum levels of TNF and IFN-γ increased in sleep-restricted C57BL/6 but not in BALB/c mice; no changes in other cytokines were found. Sleep restriction increased blood-brain barrier permeability in C57BL/6 strain but not in BALB/c. The hippocampus of sleep-restricted C57BL/6 mice exhibited an increase in the expression of the neuroinflammatory markers Iba-1, A_2A adenosine receptor, and MMP-9; meanwhile in sleep-restricted BALB/c mice the expression of this markers was lesser than the control group. These data suggest that cytokines may be playing a key role in modulating blood-brain barrier function during sleep restriction, and probably the effects are related to Iba-1, MMP-9 and A_2A adenosine receptor overexpression.

Differential induction of malaria liver pathology in mice infected with Plasmodium chabaudi AS or Plasmodium berghei NK65

BACKGROUND

Cerebral malaria and severe anaemia are the most common deadly complications of malaria, and are often associated, both in paediatric and adult patients, with hepatopathy, whose pathogenesis is not well characterized, and sometimes also with acute respiratory distress syndrome (ARDS). Here, two species of murine malaria, the lethal Plasmodium berghei strain NK65 and self-healing Plasmodium chabaudi strain AS which differ in their ability to cause hepatopathy and/or ARDS were used to investigate the lipid alterations, oxidative damage and host immune response during the infection in relation to parasite load and accumulation of parasite products, such as haemozoin.

METHODS

Plasma and livers of C57BL/6J mice injected with PbNK65 or PcAS infected erythrocytes were collected at different times and tested for parasitaemia, content of haemozoin and expression of tumour necrosis factor (TNF). Hepatic enzymes, antioxidant defenses and lipids content and composition were also evaluated.

RESULTS

In the livers of P. berghei NK65 infected mice both parasites and haemozoin accumulated to a greater extent than in livers of P. chabaudi AS infected mice although in the latter hepatomegaly was more prominent. Hepatic enzymes and TNF were increased in both models. Moreover, in P. berghei NK65 infected mice, increased lipid peroxidation, accumulation of triglycerides, impairment of anti-oxidant enzymes and higher collagen deposition were detected. On the contrary, in P. chabaudi AS infected mice the antioxidant enzymes and the lipid content and composition were normal or even lower than uninfected controls.

CONCLUSIONS

This study demonstrates that in C57BL/6J mice, depending on the parasite species, malaria-induced liver pathology results in different manifestations, which may contribute to the different outcomes. In P. berghei NK65 infected mice, which concomitantly develop lethal acute respiratory distress syndrome, the liver tissue is characterized by an excess oxidative stress response and reduced antioxidant defenses while in P. chabaudi AS infected mice hepatopathy does not lead to lipid alterations or reduction of antioxidant enzymes, but rather to inflammation and cytokine burst, as shown earlier, that may favour parasite killing and clearance of the infection. These results may help understanding the different clinical profiles described in human malaria hepatopathy.

Malaria in Children

Malaria is a leading cause of morbidity and mortality in endemic areas, leading to an estimated 438,000 deaths in 2015. Malaria is also an important health threat to travelers to endemic countries and should be considered in evaluation of any traveler returning from a malaria-endemic area who develops fever. Considering the diagnosis of malaria in patients with potential exposure is critical. Prompt provision of effective treatment limits the complications of malaria and can be life-saving. Understanding Plasmodium species variation, epidemiology, and drug-resistance patterns in the geographic area where infection was acquired is important for determining treatment choices.

Monocyte activation and cytokine production in Malawian children presenting with P. falciparum malaria

Malaria in malaria‐naïve adults is associated with an inflammatory response characterized by expression of specific activation markers on innate immune cells. Here, we investigate activation and adhesion marker expression, and cytokine production in monocytes from children presenting with cerebral malaria (CM, n = 36), severe malarial anaemia (SMA, n = 42) or uncomplicated malaria (UM, n = 66), and healthy aparasitemic children (n = 52) in Blantyre, Malawi. In all malaria groups, but particularly in the two severe malaria groups, monocyte expression of CD11b, CD11c, CD18, HLA‐DR and CD86, and percentages of TNF‐α‐ and IL‐6‐producing monocytes were lower than in healthy controls, while expression of CD11a, TLR2 and TLR4 was lower in children with severe malaria compared with controls. These levels mostly normalized during convalescence, but percentages of cytokine‐producing monocytes remained suppressed in children with SMA. In all malaria groups, especially the SMA group, a greater proportion of monocytes were loaded with haemozoin than among controls. In a P. falciparum hyperendemic area, monocytes in children with acute symptomatic malaria have reduced expression of adhesion molecules and activation markers and reduced inflammatory cytokine production. This immune suppression could be due to accumulation of haemozoin and/or previous exposure to P. falciparum.

Matrix metalloproteinase-9 polymorphism 1562 C > T (rs3918242) associated with protection against placental malaria

Phagocytosis of malaria pigment (hemozoin) induces increased activity of matrix metalloproteinase (MMP)-9, an endopeptidase involved in cytokine regulation. In this study, we examined whether a common functional MMP-9 promoter polymorphism (rs3918242) affects Plasmodium falciparum infection in pregnancy. Eighteen percent of Ghanaian primiparae carried the minor T allele. It was associated with reduced odds of placental hemozoin and of placental as well as peripheral blood parasitemia. The results indicate that a common MMP-9 polymorphism protects against placental malaria indicating that this endopeptidase is involved in susceptibility to P. falciparum.

Etiopathogenesis and Pathophysiology of Malaria

Malaria is a parasitic disease caused by Plasmodium protozoan parasites and transmitted by Anopheles mosquitoes. The disease is diffused in tropical areas, where it is associated with high morbidity and mortality. P. falciparum is the most dangerous species, mainly affecting young children. The parasite cycle occurs both in humans (asexual stages) and in mosquitoes (sexual stages). In humans, Plasmodium grows and multiplies within red blood cells using hemoglobin as essential source of nutrients and energy. However, this process generates toxic heme that the parasite aggregates into an insoluble inert biocrystal called hemozoin. This molecule sequesters in various organs (liver, spleen, and brain), potentially contributing to the development of malaria immunopathogenesis. Uncomplicated falciparum malaria clinical frame ranges from asymptomatic infection to classic symptoms such as fever, chills, sweating, headache, and muscle aches. However, malaria can also evolve into severe life-threatening complications, including cerebral malaria, severe anemia, respiratory distress, and acute renal failure.

Perioperative considerations of the patient with malaria

Purpose

Malaria is a life-threatening infectious disease caused by the Plasmodium parasite. Increased global travel has resulted in an escalation in the number of imported cases seen in developed countries. Patients with malaria may present for surgery in both endemic and non-endemic countries. This article reviews the perioperative considerations when managing patients with malaria.

Source

A literature review of anesthesia, perioperative care, and malaria-related articles was performed using the MEDLINE^®, EMBASE™, and Web of Science databases to identify relevant articles published in English during 1945-2014. Of the 303 articles matching the search criteria, 265 were excluded based on title and abstract. Eleven of the remaining 38 articles were relevant to anesthesia/perioperative care, and 27 articles were identified as having direct relevance to critical care medicine.

Principal findings

The majority of imported malaria cases are caused by the falciparum species, which is associated with the greatest degree of morbidity and mortality. Various organ systems may be impacted as a consequence of changes in the structure and function of parasitized erythrocytes. Preoperative assessment should focus on establishing the species of malaria, the severity of disease, assessing the degree of end-organ impairment, and initiating treatment of malaria prior to surgery. Intravenous artesunate is the treatment of choice for severe falciparum malaria. Quinine is a second-line agent but has a narrow therapeutic index and particularly hazardous side effects. Intraoperatively, attention should focus on fluid management, dynamics of cerebral blood flow, and avoidance of hypoglycemia. Postoperative care of severe cases should ideally take place in a critical care unit as there may be ongoing requirements for multi-organ support, including renal replacement therapy, ventilation, and/or inotropic support. The safety of neuraxial anesthesia has not been well studied in the setting of malaria.

Conclusions

Malaria remains one of the most devastating infectious diseases worldwide. Multiple organ systems can be impacted as a consequence of changes in structure and function of parasitized erythrocytes. Safe perioperative management requires a sound knowledge of all these potential system effects.

Inhibition of metalloproteinase-9 secretion and gene expression by artemisinin derivatives

Malaria remains one of the world's most common infectious diseases, being responsible for more deaths than any other communicable disease except tuberculosis. There is strong evidence that tumour necrosis factor α and interleukin-1β are important contributors to the systemic disease caused by the infection with Plasmodium falciparum. Circulating levels of TNFα are increased after infection, as a consequence of stimulation of monocyte-macrophages by infected red blood cells or parasite products, as shown in vitro for the malaria pigment haemozoin. TNFα in turn enhances the synthesis of metalloproteinase-9 in monocytes and macrophages. Metalloproteinase-9 acts on the extracellular matrix but also on non-traditional substrates, including precursors of inflammatory cytokines, which are proteolytically activated and contribute to the amplification of the inflammatory response. The aim of the present work was to establish whether artemisinin and its derivatives artemisone, artesunate and dihydroartemisinin possess immuno-modulatory properties. In particular, it is necessary to evaluate their effects on mRNA levels and secretion of MMP-9 by the human monocytic cell line (THP-1 cells) stimulated by hemozoin or TNFα. 5μM of each derivative, although not artemisinin itself, induced significantly inhibited TNFα production. Artesunate, artemisone and DHA antagonized haemozoin-induced MMP-9 secretion by 25%, 24% and 50%, respectively. mRNA levels were also depressed by 14%, 20% and 27%, respectively, thus reflecting in part the effect observed on protein production. The derivatives significantly inhibited both TNFα-induced MMP-9 secretion and mRNA levels to a greater extent than haemozoin itself. Both haemozoin and TNFα increased NF-κB driven transcription by 11 and 7.7 fold, respectively. Artesunate, artemisone and DHA inhibited haemozoin-induced NF-κB driven transcription by 28%, 34%, and 49%, respectively. Similarly the derivatives, but not artemisinin, prevented TNFα-induced NF-κB driven transcription by 47-51%. The study indicates that artemisinins may attenuate the inflammatory potential of monocytes in vivo. Thus, in addition to direct anti-parasitic activities, the beneficial clinical effects of artemisinins for the treatment of malaria include the apparent ability to attenuate the inflammatory response, thus limiting the risk of progression to the more severe form of the disease, including the onset of cerebral malaria.

Matrix metalloproteinase 9 production by monocytes is enhanced by TNF and participates in the pathology of human cutaneous Leishmaniasis

Introduction

Cutaneous leishmaniasis (CL) due to L.braziliensis infection is characterized by a strong inflammatory response with high levels of TNF and ulcer development. Less attention has been given to the role of mononuclear phagocytes to this process. Monocytes constitute a heterogeneous population subdivided into classical, intermediate and non-classical, and are known to migrate to inflammatory sites and secrete inflammatory mediators. TNF participates in the induction of matrix metalloproteinases (MMPs). MMP-9 is an enzyme that degrades basal membrane and its activity is controlled by the tissue inhibitor of metalloproteinase.

Methods

Mononuclear cells were obtained from ex-vivo labeling sub-populations of monocytes and MMP-9, and the frequency was determined by flow cytometry. Culture was performed during 72 hours, stimulating the cells with SLA, levels of MMP-9 and TIMP-1 in the supernatants were determined by ELISA.

Results

We observed that cells from CL lesions secrete high amounts of MMP-9 when compared to healthy subjects. Although MMP-9 was produced by monocytes, non-classical ones were the main source of this enzyme. We also observed that TNF produced in high level during CL contributes to MMP-9 production.

Conclusions

These observations emphasize the role of monocytes, TNF and MMP-9 in the pathogenesis of L. braziliensis infection.

To examine the participation of MMP-9 in the pathogenesis of L. braziliensis infection, we realized a cross-sectional study with CL patients in an early phase of the disease or with a classical ulcer, and healthy controls. We evaluated the frequency of MMP-9 in monocyte subsets and its mechanism of production. Our results showed that monocytes were the major cells producing MMP-9. The MMP-9 production by CL patients was presented in higher levels when compared with healthy subjects and early cutaneous leishmaniasis (ECL) patients, and the levels of MMP-9 inhibitor, TIMP-1, were lower in CL patients when compared to healthy subjects. The production of MMP-9 was enhanced by TNF, a cytokine associated with tissue damage in CL patients. Thus, therapeutic modulation of MMP-9 may be a useful approach for improving disease outcome in L. braziliensis patients.

Functional characterization of Anopheles matrix metalloprotease 1 reveals its agonistic role during sporogonic development of malaria parasites

The ability to invade tissues is a unique characteristic of the malaria stages that develop/differentiate within the mosquitoes (ookinetes and sporozoites). On the other hand, tissue invasion by many pathogens has often been associated with increased matrix metalloprotease (MMP) activity in the invaded tissues. By employing cell biology and reverse genetics, we studied the expression and explored putative functions of one of the three MMPs encoded in the genome of the malaria vector Anopheles gambiae, namely, the Anopheles gambiae MMP1 (AgMMP1) gene, during the processes of blood digestion, midgut epithelium invasion by Plasmodium ookinetes, and oocyst development. We show that AgMMP1 exists in two alternative isoforms resulting from alternative splicing; one secreted (S-MMP1) and associated with hemocytes, and one membrane type (MT-MMP1) enriched in the cell attachment sites of the midgut epithelium. MT-MMP1 showed a remarkable response to ookinete midgut invasion manifested by increased expression, enhanced zymogen maturation, and subcellular redistribution, all indicative of an implication in the midgut epithelial healing that accompanies ookinete invasion. Importantly, RNA interference (RNAi)-mediated silencing of the AgMMP1 gene revealed a postinvasion protective function of AgMMP1 during oocyst development. The combined results link for the first time an MMP with vector competence and mosquito-Plasmodium interactions.

Co-infection restrains Litomosoides sigmodontis filarial load and plasmodial P. yoelii but not P. chabaudi parasitaemia in mice

Infection with multiple parasite species is clearly the norm rather than the exception, in animals as well as in humans. Filarial nematodes and Plasmodium spp. are important parasites in human public health and they are often co-endemic. Interactions between these parasites are complex. The mechanisms underlying the modulation of both the course of malaria and the outcome of filarial infection are poorly understood. Despite increasing activity in recent years, studies comparing co- and mono-infections are very much in their infancy and results are contradictory at first sight. In this study we performed controlled and simultaneous co-infections of BALB/c mice with Litomosoides sigmodontis filaria and with Plasmodium spp. (Plasmodium yoelii 17 XNL or Plasmodium chabaudi 864VD). An analysis of pathological lesions in the kidneys and lungs and a parasitological study were conducted at different times of infection. Whatever the plasmodial species, the filarial recovery rate was strongly decreased. The peak of parasitaemia in the plasmodial infection was decreased in the course of P. yoelii infection but not in that of P. chabaudi. Regarding pathological lesions, L. sigmodontis can reverse lesions in the kidneys due to the presence of both Plasmodium species but does not modify the course of pulmonary lesions. The filarial infection induces granulomas in the lungs.

Host matrix metalloproteinases in cerebral malaria: new kids on the block against blood-brain barrier integrity?

Cerebral malaria (CM) is a life-threatening complication of falciparum malaria, associated with high mortality rates, as well as neurological impairment in surviving patients. Despite disease severity, the etiology of CM remains elusive. Interestingly, although the Plasmodium parasite is sequestered in cerebral microvessels, it does not enter the brain parenchyma: so how does Plasmodium induce neuronal dysfunction? Several independent research groups have suggested a mechanism in which increased blood–brain barrier (BBB) permeability might allow toxic molecules from the parasite or the host to enter the brain. However, the reported severity of BBB damage in CM is variable depending on the model system, ranging from mild impairment to full BBB breakdown. Moreover, the factors responsible for increased BBB permeability are still unknown. Here we review the prevailing theories on CM pathophysiology and discuss new evidence from animal and human CM models implicating BBB damage. Finally, we will review the newly-described role of matrix metalloproteinases (MMPs) and BBB integrity. MMPs comprise a family of proteolytic enzymes involved in modulating inflammatory response, disrupting tight junctions, and degrading sub-endothelial basal lamina. As such, MMPs represent potential innovative drug targets for CM.

Natural haemozoin induces expression and release of human monocyte tissue inhibitor of metalloproteinase-1

Recently matrix metalloproteinase-9 (MMP-9) and its endogenous inhibitor (tissue inhibitor of metalloproteinase-1, TIMP-1) have been implicated in complicated malaria. In vivo, mice with cerebral malaria (CM) display high levels of both MMP-9 and TIMP-1, and in human patients TIMP-1 serum levels directly correlate with disease severity. In vitro, natural haemozoin (nHZ, malarial pigment) enhances monocyte MMP-9 expression and release. The present study analyses the effects of nHZ on TIMP-1 regulation in human adherent monocytes. nHZ induced TIMP-1 mRNA expression and protein release, and promoted TNF-α, IL-1β, and MIP-1α/CCL3 production. Blocking antibodies or recombinant cytokines abrogated or mimicked nHZ effects on TIMP-1, respectively. p38 MAPK and NF-κB inhibitors blocked all nHZ effects on TIMP-1 and pro-inflammatory molecules. Still, total gelatinolytic activity was enhanced by nHZ despite TIMP-1 induction. Collectively, these data indicate that nHZ induces inflammation-mediated expression and release of human monocyte TIMP-1 through p38 MAPK- and NF-κB-dependent mechanisms. However, TIMP-1 induction is not sufficient to counterbalance nHZ-dependent MMP-9 enhancement. Future investigation on proteinase-independent functions of TIMP-1 (i.e. cell survival promotion and growth/differentiation inhibition) is needed to clarify the role of TIMP-1 in malaria pathogenesis.

Effects of Plasmodium falciparum-infected erythrocytes on matrix metalloproteinase-9 regulation in human microvascular endothelial cells

OBJECTIVE

To investigate the regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in human microvascular endothelium (HMEC-1) exposed to erythrocytes infected by different strains of Plasmodium falciparum (P. falciparum).

METHODS

HMEC-1 cells were co-incubated for 72 h with erythrocytes infected by late stage trophozoite of D10 (chloroquine-sensitive) or W2 (chloroquine-resistant) P. falciparum strains. Cell supernatants were then collected and the levels of pro- or active gelatinases MMP-9 and MMP-2 were evaluated by gelatin zymography and densitometry. The release of pro-MMP-9, MMP-3, MMP-1 and TIMP-1 proteins was analyzed by western blotting and densitometry.

RESULTS

Infected erythrocytes induced de novo proMMP-9 and MMP-9 release. Neither basal levels of proMMP-2 were altered, nor active MMP-2 was found. MMP-3 and MMP-1 secretion was significantly enhanced, whereas basal TIMP-1 was unaffected. All effects were similar for both strains.

CONCLUSIONS

P. falciparum parasites, either chloroquine-sensitive or -resistant, induce the release of active MMP-9 protein from human microvascular endothelium, by impairing balances between proMMP-9 and its inhibitor, and by enhancing the levels of its activators. This work provides new evidence on MMP involvement in malaria, pointing at MMP-9 as a possible target in adjuvant therapy.

Role of 15-hydroxyeicosatetraenoic acid in hemozoin-induced lysozyme release from human adherent monocytes

Natural hemozoin (nHZ), a lipid-bound ferriprotoporphyrin IX crystal produced by Plasmodium parasites after hemoglobin catabolism, seriously compromises the functions of human monocytes, and 15-hydroxyeicosatetraenoic acid (15-HETE) and 4-hydroxynonenal (4-HNE), two nHZ lipoperoxidation products, have been related to such a functional impairment. nHZ was recently shown to promote inflammation-mediated lysozyme release from human monocytes through p38 mitogen-activated protein kinase- (MAPK)- and nuclear factor (NF)-κB-dependent mechanisms. This study aimed at identifying the molecule of nHZ lipid moiety that was responsible for these effects. Results showed that 15-HETE mimicked nHZ effects on lysozyme release, whereas 4-HNE did not. 15-HETE-enhanced lysozyme release was abrogated by anti-TNF-α and anti-IL-1β-blocking antibodies and mimicked by recombinant cytokines; on the contrary, MIP-1α/CCL3 was not involved as a soluble mediator of 15-HETE effects. Moreover, 15-HETE early activated p38 MAPK and NF-κB pathways by inducing p38 MAPK phosphorylation; cytosolic I-κBα phosphorylation and degradation; NF-κB nuclear translocation and DNA-binding. Inhibition of both routes through chemical inhibitors (SB203580, quercetin, artemisinin, and parthenolide) prevented 15-HETE-dependent lysozyme release. Collectively, these data suggest that 15-HETE plays a major role in nHZ-enhanced monocyte degranulation.

Involvement of p38 MAPK in haemozoin-dependent MMP-9 enhancement in human monocytes

The lipid moiety of natural haemozoin (nHZ, malarial pigment) was previously shown to enhance expression and release of human monocyte matrix metalloproteinase-9 (MMP-9), and a major role for 15-(S,R)-hydroxy-6,8,11,13-eicosatetraenoic acid (15-HETE), a nHZ lipoperoxidation product, was proposed. Here, the underlying mechanisms were investigated, focusing on the involvement of mitogen-activated protein kinases (MAPKs). Results showed that nHZ promoted either early or late p38 MAPK phosphorylation; however, nHZ did not modify basal phosphorylation/expression ratios of extracellular signal-regulated kinase-1/2 and c-jun N-terminal kinase-1/2. 15-HETE mimicked nHZ effects on p38 MAPK, whereas lipid-free synthetic (s)HZ and delipidized (d)HZ did not. Consistently, both nHZ and 15-HETE also promoted phosphorylation of MAPK-activated protein kinase-2, a known p38 MAPK substrate; such an effect was abolished by SB203580, a synthetic p38 MAPK inhibitor. SB203580 also abrogated nHZ-dependent and 15-HETE-dependent enhancement of MMP-9 mRNA and protein (latent and activated forms) levels in cell lysates and supernatants. Collectively, these data suggest that in human monocytes, nHZ and 15-HETE upregulate MMP-9 expression and secretion through activation of p38 MAPK pathway. The present work provides new evidence on mechanisms underlying MMP-9 deregulation in malaria, which might be helpful to design new specific drugs for adjuvant therapy in complicated malaria.

Host-parasite interaction: parasite-derived and -induced proteases that degrade human extracellular matrix

Parasitic protozoa are among the most important pathogens worldwide. Diseases such as malaria, leishmaniasis, amoebiasis, giardiasis, trichomoniasis, and trypanosomiasis affect millions of people. Humans are constantly threatened by infections caused by these pathogens. Parasites engage a plethora of surface and secreted molecules to attach to and enter mammalian cells. The secretion of lytic enzymes by parasites into host organs mediates critical interactions because of the invasion and destruction of interstitial tissues, enabling parasite migration to other sites within the hosts. Extracellular matrix is a complex, cross-linked structure that holds cells together in an organized assembly and that forms the basement membrane lining (basal lamina). The extracellular matrix represents a major barrier to parasites. Therefore, the evolution of mechanisms for connective-tissue degradation may be of great importance for parasite survival. Recent advances have been achieved in our understanding of the biochemistry and molecular biology of proteases from parasitic protozoa. The focus of this paper is to discuss the role of protozoan parasitic proteases in the degradation of host ECM proteins and the participation of these molecules as virulence factors. We divide the paper into two sections, extracellular and intracellular protozoa.

Haemozoin induces early cytokine-mediated lysozyme release from human monocytes through p38 MAPK- and NF-kappaB-dependent mechanisms

Malarial pigment (natural haemozoin, HZ) is a ferriprotoporphyrin IX crystal produced by Plasmodium parasites after haemoglobin catabolism. HZ-fed human monocytes are functionally compromised, releasing increased amounts of pro-inflammatory molecules, including cytokines, chemokines and cytokine-related proteolytic enzyme Matrix Metalloproteinase-9 (MMP-9), whose role in complicated malaria has been recently suggested. In a previous work HZ was shown to induce through TNFalpha production the release of monocytic lysozyme, an enzyme stored in gelatinase granules with MMP-9. Here, the underlying mechanisms were investigated. Results showed that HZ lipid moiety promoted early but not late lysozyme release. HZ-dependent lysozyme induction was abrogated by anti-TNFalpha/IL-1beta/MIP-1alpha blocking antibodies and mimicked by recombinant cytokines. Moreover, HZ early activated either p38 MAPK or NF-kappaB pathways by inducing: p38 MAPK phosphorylation; cytosolic I-kappaBalpha phosphorylation and degradation; NF-kappaB nuclear translocation and DNA-binding. Inhibition of both routes through selected molecules (SB203580, quercetin, artemisinin, parthenolide) prevented HZ-dependent lysozyme release. These data suggest that HZ-triggered overproduction of TNFalpha, IL-1beta and MIP-1alpha mediates induction of lysozyme release from human monocytes through activation of p38 MAPK and NF-kappaB pathways, providing new evidence on mechanisms underlying the HZ-enhanced monocyte degranulation in falciparum malaria and the potential role for lysozyme as a new affordable marker in severe malaria.

Activation of nuclear factor kappa B in peripheral blood mononuclear cells from malaria patients

BACKGROUND

Malaria parasites and their products can activate a specific immune response by stimulating cytokine production in the host's immune cells. Transcription nuclear factor kappa B (NF-κB) is an important regulator for the control of many pro-inflammatory genes, such as interleukin-1 (IL-1) and tumor necrosis factor (TNF). The activation and expression of NF-κB p65 in peripheral blood mononuclear cells (PBMCs) of malaria patients were investigated and correlated with the levels of IL-10 and TNF to study the nature of NF-κB p65 and its linkage to inflammatory cytokines.

METHODS

The sample group comprised 33 patients admitted with malaria caused by Plasmodium vivax (n = 11), uncomplicated Plasmodium falciparum (n = 11), and complicated Plasmodium falciparum (n = 11). Peripheral blood was collected at admission and on day 7 for PBMC isolation. Healthy subjects were used as a control group. The expressions of NF-κB p65 in the PBMCs from malaria patients and the plasma levels of IL-10 and TNF were measured by using enzyme-linked immunosorbent assay (ELISA). The immunofluorescence technique was used to determine NF-κB nuclear translocation.

RESULTS

At admission, patients with P. vivax and uncomplicated P. falciparum had significantly elevated phospho-NF-κB p65 levels in the PBMCs compared with those of healthy controls. However, patients with complicated P. falciparum malaria had decreased levels of phospho-NF-κB p65. On day 7 post-treatment, significantly increased phospho-NF-κB p65 was found in the PBMCs of patients with complicated P. falciparum, compared with healthy controls. The plasma level of IL-10 was elevated in day 0 in patients with complicated P. falciparum malaria and was found to be negatively correlated with phospho-NF-κB p65 level (rs = -0.630, p = 0.038). However, there was no correlation between phospho-NF-κB p65 expression and TNF level in patients with complicated P. falciparum malaria.

CONCLUSIONS

This is the first report demonstrating alterations in NF-κB p65 activity in the PBMCs of malaria patients. The altered lower features of NF-κB p65 in the PBMCs of patients with complicated P. falciparum at admission could be due to a suppressive effect of high IL-10 associated with complicated P. falciparum malaria.

Digestive vacuole of Plasmodium falciparum released during erythrocyte rupture dually activates complement and coagulation

Severe Plasmodium falciparum malaria evolves through the interplay among capillary sequestration of parasitized erythrocytes, deregulated inflammatory responses, and hemostasis dysfunction. After rupture, each parasitized erythrocyte releases not only infective merozoites, but also the digestive vacuole (DV), a membrane-bounded organelle containing the malaria pigment hemozoin. In the present study, we report that the intact organelle, but not isolated hemozoin, dually activates the alternative complement and the intrinsic clotting pathway. Procoagulant activity is destroyed by phospholipase C treatment, indicating a critical role of phospholipid head groups exposed at the DV surface. Intravenous injection of DVs caused alternative pathway complement consumption and provoked apathy and reduced nociceptive responses in rats. Ultrasonication destroyed complement-activating and procoagulant properties in vitro and rendered the DVs biologically inactive in vivo. Low-molecular-weight dextran sulfate blocked activation of both complement and coagulation and protected animals from the harmful effects of DV infusion. We surmise that in chronic malaria, complement activation by and opsonization of the DV may serve a useful function in directing hemozoin to phagocytic cells for safe disposal. However, when the waste disposal system of the host is overburdened, DVs may transform into a trigger of pathology and therefore represent a potential therapeutic target in severe malaria.

115 kDa serine protease confers sustained protection to visceral leishmaniasis caused by Leishmania donovani via IFN-γ induced down-regulation of TNF-α mediated MMP-9 activity

Visceral leishmaniasis caused by the intracellular parasite Leishmania donovani is a major public health problem in the developing world. The emergence of increasing number of L. donovani strains resistance to antimonial drugs recommended worldwide requires the intervention of effective vaccine strategy for treatment of VL. In the present study L. donovani culture derived, soluble, secretory serine protease (pSP) has been shown to be vaccine target of VL. Protection from VL could be achieved by the use of safer vaccine which generally requires an adjuvant for induction of strong Th1 response. To assess the safety, immunogenicity and efficacy of pSP as vaccine candidate in mouse model we used IL-12 as adjuvant. BALB/c mice immunized with pSP+IL-12 were protected significantly from challenged infection even after four months by reducing the parasite load in liver and spleen and suppressed the development of the disease along with an increase in IgG2a antibody level in serum, enhanced delayed type hypersensitivity and strong T-cell proliferation. Groups receiving pSP+IL-12 had an augmented pSP antigen specific Th1 cytokines like IFN-γ and TNF-α response with concomitant decrease of Th2 cytokines IL-4 and IL-10 after vaccination. In this study the vaccine efficacy of pSP was further assessed for its prophylactic potential by enumerating matrix metalloprotease-9 (MMP-9) profile which has been implicated in various diseases. MMP-9 associated with different microbial infections is controlled by their natural inhibitors (TIMPS) and by some cytokines. In this study pSP was found to regulate excessive inflammation by modulating the balance between MMP-9 and TIMP-1 expression. This modulatory effect has also been demonstrated by IFN-γ mediated down regulation of TNF-α induced MMP-9 expression in activated murine macrophages. This is the first report where a secretory L. donovani serine protease (pSP) adjuvanted with IL-12 could also act as protective imunogen by modifying cytokine mediated MMP-9 expression in experimental VL. These findings elucidate the mechanisms of regulation of MMP-9 following infection of L. donovani in vaccinated animals and thus pave the way for developing new immunotherapeutic interventions for VL.

Macrophage inflammatory protein-1alpha mediates matrix metalloproteinase-9 enhancement in human adherent monocytes fed with malarial pigment

OBJECTIVE

To investigate the role of macrophage inflammatory protein-1alpha (MIP-1alpha) in the detrimental enhancement of matrix metalloproteinase-9 (MMP-9) expression, release and activity induced by phagocytosis of malarial pigment (haemozoin, HZ) in human monocytes.

METHODS

Human adherent monocytes were unfed/fed with native HZ for 2 h. After 24 hours, MIP-1alpha production was evaluated by ELISA in cell supernatants. Alternatively, HZ-unfed/fed monocytes were treated in presence/absence of anti-human MIP-1alpha blocking antibodies or recombinant human MIP-1alpha for 15 h (RNA studies) or 24 h (protein studies); therefore, MMP-9 mRNA expression was evaluated in cell lysates by Real Time RT-PCR, whereas proMMP-9 and active MMP-9 protein release were measured in cell supernatants by Western blotting and gelatin zymography.

RESULTS

Phagocytosis of HZ by human monocytes increased production of MIP-1 alpha, mRNA expression of MMP-9 and protein release of proMMP-9 and active MMP-9. All the HZ-enhancing effects on MMP-9 were abrogated by anti-human MIP-1alpha blocking antibodies and mimicked by recombinant human MIP-1alpha.

CONCLUSIONS

The present work suggests a role for MIP-1alpha in the HZ-dependent enhancement of MMP-9 expression, release and activity observed in human monocytes, highlighting new detrimental effects of HZ-triggered proinflammatory response by phagocytic cells in falciparum malaria.

Cerebral malaria pathogenesis: revisiting parasite and host contributions

Cerebral malaria is one of a number of clinical syndromes associated with infection by human malaria parasites of the genus Plasmodium. The etiology of cerebral malaria derives from sequestration of parasitized red cells in brain microvasculature and is thought to be enhanced by the proinflammatory status of the host and virulence characteristics of the infecting parasite variant. In this article we examine the range of factors thought to influence the development of Plasmodium falciparum cerebral malaria in humans and review the evidence to support their role.

Matrix metalloproteinases as therapeutic targets in protozoan parasitic infections

Matrix metalloproteinases (MMPs) are associated with processes of tissue remodeling and are expressed in all infections with protozoan parasites. We here report the status of MMP research in malaria, trypanosomiasis, leishmaniasis and toxoplasmosis. In all these infections, the balances between MMPs and endogenous MMP inhibitors are disturbed, mostly in favor of active proteolysis. When the infection is associated with leukocyte influx into specific organs, immunopathology and collateral tissue damage may occur. These pathologies include cerebral malaria, sleeping sickness (human African trypanosomiasis), Chagas disease (human American trypanosomiasis), leishmaniasis and toxoplasmic encephalitis in immunocompromised hosts. Destruction of the integrity of the blood-brain barrier (BBB) is a common denominator that may be executed by leukocytic MMPs under the control of host cytokines and chemokines as well as influenced by parasite products. Mechanisms by which parasite-derived products alter host expression of MMP and endogenous MMP inhibitors, have only been described for hemozoin (Hz) in malaria. Hence, understanding these interactions in other parasitic infections remains an important challenge. Furthermore, the involved parasites are also known to produce their own metalloproteinases, and this forms an extra stimulus to investigate MMP inhibitory drugs as therapeutics. MMP inhibitors (MMPIs) may dampen collateral tissue damage, as is anecdotically reported for tetracyclines as MMP regulators in parasite infections.

Digestive vacuoles of Plasmodium falciparum are selectively phagocytosed by and impair killing function of polymorphonuclear leukocytes

Sequestration of parasitized erythrocytes and dysregulation of the coagulation and complement system are hallmarks of severe Plasmodium falciparum malaria. A link between these events emerged through the discovery that the parasite digestive vacuole (DV), which is released together with infective merozoites into the bloodstream, dually activates the intrinsic clotting and alternative complement pathway. Complement attack occurs exclusively on the membrane of the DVs, and the question followed whether DVs might be marked for uptake by polymorphonuclear granulocytes (PMNs). We report that DVs are indeed rapidly phagocytosed by PMNs after schizont rupture in active human serum. Uptake of malaria pigment requires an intact DV membrane and does not occur when the pigment is extracted from the organelle. Merozoites are not opsonized and escape phagocytosis in nonimmune serum. Antimalarial Abs mediate some uptake of the parasites, but to an extent that is not sufficient to markedly reduce reinvasion rates. Phagocytosis of DVs induces a vigorous respiratory burst that drives the cells into a state of functional exhaustion, blunting the production of reactive oxygen species (ROS) and microbicidal activity upon challenge with bacterial pathogens. Systemic overloading of PMNs with DVs may contribute to the enhanced susceptibility of patients with severe malaria toward invasive bacterial infections.

Natural haemozoin modulates matrix metalloproteinases and induces morphological changes in human microvascular endothelium

Severe malaria, including cerebral malaria (CM), is characterized by the sequestration of parasitized erythrocytes in the microvessels after cytoadherence to endothelial cells. Products of parasite origin, such as haemozoin (HZ), contribute to the pathogenesis of severe malaria by interfering with host inflammatory response. In human monocytes, HZ enhanced the levels of matrix metalloproteinase-9 (MMP-9), a protease involved in neuroinflammation. Here the effects of HZ on the regulation of MMPs by the human microvascular endothelial cell line HMEC-1 were investigated. Cells treated with natural (n)HZ appeared elongated instead of polygonal, and formed microtubule-like vessels on synthetic basement membrane. nHZ enhanced total gelatinolytic activity by inducing proMMP-9 and MMP-9 without affecting basal MMP-2. The level of the endogenous tissue inhibitor of MMP-9 (TIMP-1) was not altered by nHZ, while TIMP-2, the MMP-2 inhibitor, was enhanced. Additionally, nHZ induced MMP-1 and MMP-3, two enzymes sequentially involved in collagenolysis and proMMP-9 proteolytic activation. Lipid-free HZ did not reproduce nHZ effects. Present data suggest that the lipid moiety of HZ alters the MMP/TIMP balances and promotes the proteolytic activation of proMMP-9 in HMEC-1, thereby enhancing total gelatinolytic activity, cell activation and inflammation. These findings might help understanding the mechanisms of blood brain barrier damage during CM.

Matrix Metalloproteinase-9 and Haemozoin: Wedding Rings for Human Host and Plasmodium falciparum Parasite in Complicated Malaria

It is generally accepted that the combination of both Plasmodium falciparum parasite and human host factors is involved in the pathogenesis of complicated severe malaria, including cerebral malaria (CM). Among parasite products, the malarial pigment haemozoin (HZ) has been shown to impair the functions of mononuclear and endothelial cells. Different CM models were associated with enhanced levels of matrix metalloproteinases (MMPs), a family of proteolytic enzymes able to disrupt subendothelial basement membrane and tight junctions and shed, activate, or inactivate cytokines, chemokines, and other MMPs through cleavage from their precursors. Among MMPs, a good candidate for targeted therapy might be MMP-9, whose mRNA and protein expression enhancement as well as direct proenzyme activation by HZ have been recently investigated in a series of studies by our group and others. In the present paper the role of HZ and MMP-9 in complicated malaria, as well as their interactions, will be discussed.

Role of the NF-κB transcription pathway in the haemozoin- and 15-HETE-mediated activation of matrix metalloproteinase-9 in human adherent monocytes

Haemozoin (HZ, malarial pigment) is a crystalline ferriprotoporphyrin IX polymer derived from undigested host haemoglobin haem, present in late stages of Plasmodium falciparum-parasitized RBCs and in residual bodies shed after schizogony. It was shown previously that phagocytosed HZ or HZ-containing trophozoites increased monocyte matrix metalloproteinase-9 (MMP-9) activity and enhanced production of MMP-9-related cytokines TNF and IL-1beta. Here we show that in human monocytes the HZ/trophozoite phagocytosis effects and their recapitulation by 15(S,R)-hydroxy-6,8,11,13-eicosatetraenoic acid (15-HETE), a potent lipoperoxidation derivative generated by HZ from arachidonic acid via haem catalysis, were mediated via activation of NF-κB transcription pathway. After phagocytosis of HZ/trophozoites or treatment with 15-HETE, the NF-κB complex migrated to the nuclear fraction while the inhibitory cytosolic IκBalpha protein was phosphorylated and degraded. All HZ/trophozoite/15-HETE effects on MMP-9 activity and TNF/IL-1beta production were abrogated by quercetin, artemisinin and parthenolide, inhibitors of IκBalpha phosphorylation and subsequent degradation, NF-κB nuclear translocation, and NF-κB-p65 binding to DNA respectively. In conclusion, enhanced activation of MMP-9, and release of pro-inflammatory cytokines TNF and IL-1beta, a triad of effects involved in malaria pathogenesis, elicited in human monocytes by trophozoite and HZ phagocytosis and recapitulated by 15-HETE, appear to be causally connected to persisting activation of the NF-κB system.

Comparative analysis of gene expression changes mediated by individual constituents of hemozoin

Plasmodium protozoa, the source of malarial infections, catabolize large quantities of hemoglobin during an intraerythrocytic phase. During this process, free heme is detoxified through biomineralization into an insoluble heme aggregate, hemozoin (Hz). In its native state, Hz is associated with a variety of lipid peroxidation products including 4-hydroxy-2-nonenal (HNE). In the present study, gene expression profiles were used to compare responses to two of the individual components of Hz in a model macrophage cell line. LPS-stimulated RAW 264.7 cells were exposed to HNE and the synthetic form of Hz, beta-hematin (BH), for 6 or 24 h. Microarray analysis identified alterations in gene expression induced by exposure to HNE and opsonized BH (fold change, > or = 1.8; p value, < or = 0.01). Patterns of gene expression were compared to changes induced by an opsonized control latex bead challenge in LPS-stimulated cells and revealed that the BH response was predominantly phagocytic. Ingenuity Pathway Analysis demonstrated that HNE mediated a short-term oxidative stress response and had a prolonged effect on the expression of genes associated with categories of "Cell Cycle", "Cellular Assembly and Organization", "DNA Replication, Recombination, and Repair", and "Cellular Development". Comparisons of expression changes caused by BH and HNE with those observed during malarial infection suggest that BH and HNE are involved in inflammatory response modulation, altered NF-kappaB signal transduction, extracellular matrix (ECM) degradation, and dyserythropoiesis. HNE exposure led to several significant steady-state expression changes including repressed chemokine (C-C motif) ligand 5 (Ccl5), indicative of dyserythropoiesis, and a severe matrix metalloproteinase 9 (Mmp9)/tissue inhibitor of metalloproteinase 1 (Timp1) imbalance in favor of ECM proteolysis.

Involvement of inflammatory chemokines in survival of human monocytes fed with malarial pigment

Hemozoin (HZ)-fed monocytes are exposed to strong oxidative stress, releasing large amounts of peroxidation derivatives with subsequent impairment of numerous functions and overproduction of proinflammatory cytokines. However, the histopathology at autopsy of tissues from patients with severe malaria showed abundant HZ in Kupffer cells and other tissue macrophages, suggesting that functional impairment and cytokine production are not accompanied by cell death. The aim of the present study was to clarify the role of HZ in cell survival, focusing on the qualitative and temporal expression patterns of proinflammatory and antiapoptotic molecules. Immunocytochemical and flow cytometric analyses showed that the long-term viability of human monocytes was unaffected by HZ. Short-term analysis by macroarray of a complete panel of cytokines and real-time reverse transcription (RT)-PCR experiments showed that HZ immediately induced interleukin-1β (IL-1β) gene expression, followed by transcription of eight additional chemokines (IL-8, epithelial cell-derived neutrophil-activating peptide 78 [ENA-78], growth-regulated oncogene α [GROα], GROβ, GROγ, macrophage inflammatory protein 1α [MIP-1α], MIP-1β, and monocyte chemoattractant protein 1 [MCP-1]), two cytokines (tumor necrosis factor alpha [TNF-α] and IL-1receptor antagonist [IL-1RA]), and the cytokine/chemokine-related proteolytic enzyme matrix metalloproteinase 9 (MMP-9). Furthermore, real-time RT-PCR showed that 15-HETE, a potent lipoperoxidation derivative generated by HZ through heme catalysis, recapitulated the effects of HZ on the expression of four of the chemokines. Intermediate-term investigation by Western blotting showed that HZ increased expression of HSP27, a chemokine-related protein with antiapoptotic properties. Taken together, the present data suggest that apoptosis of HZ-fed monocytes is prevented through a cascade involving 15-HETE-mediated upregulation of IL-1β transcription, rapidly sustained by chemokine, TNF-α, MMP-9, and IL-1RA transcription and upregulation of HSP27 protein expression.

Ellagitannins of the fruit rind of pomegranate (Punica granatum) antagonize in vitro the host inflammatory response mechanisms involved in the onset of malaria

Background

The sun-dried rind of the immature fruit of pomegranate (Punica granatum) is presently used as a herbal formulation (OMARIA, Orissa Malaria Research Indigenous Attempt) in Orissa, India, for the therapy and prophylaxis of malaria. The pathogenesis of cerebral malaria, a complication of the infection by Plasmodium falciparum, is an inflammatory cytokine-driven disease associated to an up-regulation and activity of metalloproteinase-9 and to the increase of TNF production. The in vitro anti-plasmodial activity of Punica granatum (Pg) was recently described. The aim of the present study was to explore whether the anti-malarial effect of OMARIA could also be sustained via other mechanisms among those associated to the host immune response.

Methods

From the methanolic extract of the fruit rind, a fraction enriched in tannins (Pg-FET) was prepared. MMP-9 secretion and expression were evaluated in THP-1 cells stimulated with haemozoin or TNF. The assays were conducted in the presence of the Pg-FET and its chemical constituents ellagic acid and punicalagin. The effect of urolithins, the ellagitannin metabolites formed by human intestinal microflora, was also investigated.

Results

Pg-FET and its constituents inhibited the secretion of MMP-9 induced by haemozoin or TNF. The effect occurred at transcriptional level since MMP-9 mRNA levels were lower in the presence of the tested compounds. Urolithins as well inhibited MMP-9 secretion and expression. Pg-FET and pure compounds also inhibited MMP-9 promoter activity and NF-kB-driven transcription.

Conclusions

The beneficial effect of the fruit rind of Punica granatum for the treatment of malarial disease may be attributed to the anti-parasitic activity and the inhibition of the pro-inflammatory mechanisms involved in the onset of cerebral malaria.

High levels of serum matrix metalloproteinases in dogs with natural visceral leishmaniosis: a preliminary report

The hallmark microscopic lesion in canine visceral leishmaniosis is the accumulation of lymphocytes and macrophages parasitized by amastigotes of Leishmania in the lymphoid organs. Matrix metalloproteinase (MMP)-2 and MMP-9 are important for leukocyte migration as they degrade the type IV collagen in the basal lamina. Sera from 65 dogs, 53 with serological diagnosis of visceral leishmaniosis and 12 healthy ones, were analysed by gelatin-zymography to detect MMP-2 and MMP-9 activity. The infected dogs presented higher levels of serum mature MMP-9, proMMP-9 and proMMP-2 than control dogs. No mature MMP-2 activity was observed. The levels of mature and proMMP-9 were highly correlated. These findings suggest that the multi-systemic inflammatory lesions observed in visceral leishmaniosis are associated with an increase in serum MMPs, especially MMP-9. In concert with other clinical data, quantification of serum MMP-9 in infected dogs may lead to a better understanding of the pathogenesis of visceral leishmaniosis.

Chronic infection during placental malaria is associated with up-regulation of cycloxygenase-2

BACKGROUND

Placental malaria (PM) is associated with poor foetal development, but the pathophysiological processes involved are poorly understood. Cyclooxygenase (COX) and lipoxygenase (LOX) which convert fatty acids to prostaglandins and leukotrienes, play important roles in pregnancy and foetal development. COX-2, currently targeted by specific drugs, plays a dual role as it associates with both pre-eclampsia pathology and recovery during infection. The role of COX during PM was questioned by quantifying at delivery COX-1, COX-2, 15-LOX, and IL-10 expression in two groups of malaria infected and uninfected placenta.

METHODS

Placental biopsies were collected at delivery for mRNA isolation and quantification, using real time PCR.

RESULTS

COX-2 and IL-10 mRNAs increased mainly during chronic infections (nine- and five-times, respectively), whereas COX-1 transcripts remained constant. COX-2 over-expression was associated with a higher birth weight of the baby, but with a lower rate of haemoglobin of the mother. It was associated with a macrophage infiltration of the placenta and with a low haemozoin infiltration. In the opposite way, placental infection was associated with lower expression of 15-LOX mRNA. A high degree of haemozoin deposition correlates with low birth weight and decreased expression of COX-2.

CONCLUSION

These data provide evidence that COX-2 and IL-10 are highly induced during chronic infection of the placenta, but were not associated with preterm delivery or low birth weight. The data support the involvement of COX-2 in the recovery phase of the placental infection.

Hemozoin (malarial pigment) directly promotes apoptosis of erythroid precursors

Severe malarial anemia is the most common syndrome of severe malaria in endemic areas. The pathophysiology of chronic malaria is characterised by a striking degree of abnormal development of erythroid precursors (dyserythropoiesis) and an inadequate erythropoietic response in spite of elevated levels of erythropoietin. The cause of dyserythropoiesis is unclear although it has been suggested that bone-marrow macrophages release cytokines, chemokines or lipo-peroxides after exposure to hemozoin, a crystalloid form of undigested heme moieties from malarial infected erythrocytes, and so inhibit erythropoiesis. However, we have previously shown that hemozoin may directly inhibit erythroid development in vitro and the levels of hemozoin in plasma from patients with malarial anemia and hemozoin within the bone marrow was associated with reduced reticulocyte response. We hypothesized that macrophages may reduce, not enhance, the inhibitory effect of hemozoin on erythropoiesis. In an in vitro model of erythropoiesis, we now show that inhibition of erythroid cell development by hemozoin isolated from P. falciparum is characterised by delayed expression of the erythroid markers and increased apoptosis of progenitor cells. Crucially, macrophages appear to protect erythroid cells from hemozoin, consistent with a direct contribution of hemozoin to the depression of reticulocyte output from the bone marrow in children with malarial anemia. Moreover, hemozoin isolated from P. falciparum in vitro inhibits erythroid development independently of inflammatory mediators by inducing apoptotic pathways that not only involve activation of caspase 8 and cleavage of caspase 3 but also loss of mitochondrial potential. Taken together these data are consistent with a direct effect of hemozoin in inducing apoptosis in developing erythroid cells in malarial anemia. Accumulation of hemozoin in the bone marrow could therefore result in inadequate reticulocytosis in children that have adequate levels of circulating erythropoietin.