Effect of iron chelation therapy on recovery from deep coma in children with cerebral malaria

One advantageous reflection of iron metabolism in context of normal physiology and pathological phases

PURPOSE (BACKGROUND)

The presented review is an updating of Iron metabolism in context of normal physiology and pathological phases. Iron is one of the vital elements in humans and associated into proteins as a component of heme (e.g. hemoglobin, myoglobin, cytochromes proteins, myeloperoxidase, nitric oxide synthetases), iron sulfur clusters (e.g. respiratory complexes I-III, coenzyme Q10, mitochondrial aconitase, DNA primase), or other functional groups (e.g. hypoxia inducible factor prolyl hydroxylases). All these entire iron-containing proteins ar e needed for vital cellular and organismal functions together with oxygen transport, mitochondrial respiration, intermediary and xenobiotic metabolism, nucleic acid replication and repair, host defense, and cell signaling.

METHODS (METABOLIC STRATEGIES)

Cells have developed metabolic strategies to import and employ iron safely. Regulatory process of iron uptake, storage, intracellular trafficking and utilization is vital for the maintenance of cellular iron homeostasis. Cellular iron utilization and intracellular iron trafficking pathways are not well established and very little knowledge about this. The predominant organs, which are associated in the metabolism of iron, are intestine, liver, bone marrow and spleen. Iron is conserved, recycled and stored. The reduced bioavailability of iron in humans has developed extremely efficient mechanisms for iron conservation. Prominently, the losses of iron cannot considerably enhance through physiologic mechanisms, even if iron intake and stores become excessive. Loss of iron is balanced or maintained from dietary sources.

RESULTS (OUTCOMES)

Numerous physiological abnormalities are associated with impaired iron metabolism. These abnormalities are appeared in the form of several diseases. There are duodenal ulcer, inflammatory bowel disease, sideroblastic anaemia, congenital dyserythropoietic anemias and low-grade myelodysplastic syndromes. Hereditary hemochromatosis and anaemia are two chronic diseases, which are responsible for disturbing the iron metabolism in various tissues, including the spleen and the intestine. Impairment in hepatic hepcidin synthesis is responsible for chronic liver disease, which is grounding from alcoholism or viral hepatitis. This condition directs to iron overload that can cause further hepatic damage. Iron has important role in several infectious diseases are tuberculosis, malaria trypanosomatid diseases and acquired immunodeficiency syndrome (AIDS). Iron is also associated with Systemic lupus erythematosus [SLE], cancer, Alzheimer's disease (AD) and post-traumatic epilepsy.

CONCLUSION

Recently, numerous research studies are gradually more dedicated in the field of iron metabolism, but a number of burning questions are still waiting for answer. Cellular iron utilization and intracellular iron trafficking pathways are not well established and very little knowledge about this. Increased information of the physiology of iron homeostasis will support considerate of the pathology of iron disorders and also make available the support to advance treatment.

Why is Babesia not killed by artemisinin like Plasmodium?

Babesia spp. are intraerythrocytic apicomplexans that digest and utilize red blood cells in a similar way to intraerythrocytic Plasmodium spp., but unlike the latter, are not sensitive to artemisinin. A comparison of Babesia and Plasmodium genomes revealed that Babesia genomes, which are smaller than those of Plasmodium, lack numerous genes, and especially haem synthesis-related genes, that are found in the latter. Single-cell sequencing analysis showed that the different treatment groups of Babesia microti with expressed pentose phosphate pathway-related, DNA replication-related, antioxidation-related, glycolysis-related, and glutathione-related genes were not as sensitive to artemether as Plasmodium yoelii 17XNL. In particular, pentose phosphate pathway-related, DNA replication-related, and glutathione-related genes, which were actively expressed in P. yoelii 17XNL, were not actively expressed in B. microti. Supplying iron in vivo can promote the reproduction of B. microti. These results suggest that Babesia spp. lack a similar mechanism to that of malaria parasites through which the haem or iron in hemoglobin is utilized, and that this likely leads to their insensitivity to artemisinin.

Synthesis and antimalarial activity of amide and ester conjugates of siderophores and ozonides

Despite advances in chemotherapeutic interventions for the treatment of malaria, there is a continuing need for the development of new antimalarial agents. Previous studies indicated that co-administration of chloroquine with antioxidants such as the iron chelator deferoxamine (DFO) prevented the development of persistent cognitive damage in surrogate models of cerebral malaria. The work described herein reports the syntheses and antimalarial activities of covalent conjugates of both natural (siderophores) and artificial iron chelators, namely DFO, ferricrocin and ICL-670, with antimalarial 1,2,4-trioxolanes (ozonides). All of the synthesized conjugates had potent antimalarial activities against the in vitro cultures of drug resistant and drug sensitive strains of Plasmodium falciparum. The work described herein provides the basis for future development of covalent combination of iron chelators and antimalarial chemotherapeutic agents for the treatment of cerebral malaria.

Targeting the CD146/Galectin-9 axis protects the integrity of the blood-brain barrier in experimental cerebral malaria

Cerebral malaria (CM) is a life-threatening diffuse encephalopathy caused by Plasmodium falciparum, in which the destruction of the blood-brain barrier (BBB) is the main cause of death. However, increasing evidence has shown that antimalarial drugs, the current treatment for CM, do little to protect against CM-induced BBB damage. Therefore, a means to alleviate BBB dysfunction would be a promising adjuvant therapy for CM. The adhesion molecule CD146 has been reported to be expressed in both endothelial cells and proinflammatory immune cells and mediates neuroinflammation. Here, we demonstrate that CD146 expressed on BBB endothelial cells but not immune cells is a novel therapeutic target in a mouse model of experimental cerebral malaria (eCM). Endothelial CD146 is upregulated during eCM development and facilitates the sequestration of infected red blood cells (RBCs) and/or proinflammatory lymphocytes in CNS blood vessels, thereby promoting the disruption of BBB integrity. Mechanistic studies showed that the interaction of CD146 and Galectin-9 contributes to the aggregation of infected RBCs and lymphocytes. Deletion of endothelial CD146 or treatment with the anti-CD146 antibody AA98 prevents severe signs of eCM, such as limb paralysis, brain vascular leakage, and death. In addition, AA98 combined with the antiparasitic drug artemether improved the cognition and memory of mice with eCM. Taken together, our findings suggest that endothelial CD146 is a novel and promising target in combination with antiparasitic drugs for future CM therapies.

Liposomes for malaria management: the evolution from 1980 to 2020

Malaria is one of the most prevalent parasitic diseases and the foremost cause of morbidity in the tropical regions of the world. Strategies for the efficient management of this parasitic infection include adequate treatment with anti-malarial therapeutics and vaccination. However, the emergence and spread of resistant strains of malaria parasites to the majority of presently used anti-malarial medications, on the other hand, complicates malaria treatment. Other shortcomings of anti-malarial drugs include poor aqueous solubility, low permeability, poor bioavailability, and non-specific targeting of intracellular parasites, resulting in high dose requirements and toxic side effects. To address these limitations, liposome-based nanotechnology has been extensively explored as a new solution in malaria management. Liposome technology improves anti-malarial drug encapsulation, bioavailability, target delivery, and controlled release, resulting in increased effectiveness, reduced resistance progression, and fewer adverse effects. Furthermore, liposomes are exploited as immunological adjuvants and antigen carriers to boost the preventive effectiveness of malaria vaccine candidates. The present review discusses the findings from studies conducted over the last 40 years (1980-2020) using in vitro and in vivo settings to assess the prophylactic and curative anti-malarial potential of liposomes containing anti-malarial agents or antigens. This paper and the discussion herein provide a useful resource for further complementary investigations and may pave the way for the research and development of several available and affordable anti-malarial-based liposomes and liposomal malaria vaccines by allowing a thorough evaluation of liposomes developed to date for the management of malaria.

Ferritin: An Inflammatory Player Keeping Iron at the Core of Pathogen-Host Interactions

Iron is an essential element for virtually all cell types due to its role in energy metabolism, nucleic acid synthesis and cell proliferation. Nevertheless, if free, iron induces cellular and organ damage through the formation of free radicals. Thus, iron levels must be firmly controlled. During infection, both host and microbe need to access iron and avoid its toxicity. Alterations in serum and cellular iron have been reported as important markers of pathology. In this regard, ferritin, first discovered as an iron storage protein, has emerged as a biomarker not only in iron-related disorders but also in inflammatory diseases, or diseases in which inflammation has a central role such as cancer, neurodegeneration or infection. The basic research on ferritin identification and functions, as well as its role in diseases with an inflammatory component and its potential as a target in host-directed therapies, are the main considerations of this review.

Molecular targets in cerebral malaria for developing novel therapeutic strategies

Cerebral malaria (CM) is the severe neurological complication associated with Plasmodium falciparum infection. In clinical settings CM is predominantly characterized by fever, epileptic seizures, and asexual forms of parasite on blood smears, coma and even death. Cognitive impairment in the children and adults even after survival is one of the striking consequences of CM. Poor diagnosis often leads to inappropriate malaria therapy which in turn progress into a severe form of disease. Activation of multiple cell death pathways such as Inflammation, oxidative stress, apoptosis and disruption of blood brain barrier (BBB) plays critical role in the pathogenesis of CM and secondary brain damage. Thus, understanding such mechanisms of neuronal cell death might help to identify potential molecular targets for CM. Mitigation strategies for mortality rate and long-term cognitive deficits caused by existing anti-malarial drugs still remains a valid research question to ask. In this review, we discuss in detail about critical neuronal cell death mechanisms and the overall significance of adjunctive therapy with recent trends, which provides better insight towards establishing newer therapeutic strategies for CM.

Effects of iron chelating agent on Schistosoma mansoni infected murine model

Schistosomiasis is one of the major health problems in many tropical and developing countries. Infection takes place once cerceriae penetrate human skin, then it changed into schistosomules. The schistosomules takes iron in the form of heme from host's haemoglobin, ferritin and transferrin. Iron is a vital element not only for growth and sexual maturity of schistosomules to adults but also for oogenesis. Since the trapped eggs are the pathological causative agent for most of pathogenesis and complications, the current work was designed to study the effects of early deprivation of schistosomules from iron in the host (in vivo) by chelating it with deferoxamine (DFO). The iron chelation has effects on growth, maturity and egg deposition, as well as it has ameliorative effects on liver pathology such as hepatic fibrosis. Mice were classified into four groups, normal control, DFO treated only, Schistosoma mansoni (S. mansoni) infected DFO untreated and S. mansoni infected DFO treated. The infected DFO treated mice showed significant reduction in fecal egg excretion with increased percentage of dead eggs and this was accompanied with a significant reduction of both total worm burden and hepatic egg load and increased dead egg percentage compared to the infected DFO untreated group. There was also a significant reduction in both serum and hepatic tissue ferritin concentrations in the infected DFO treated mice in comparison to the infected DFO untreated group. Additionally, a significant decrease in number and size of granulomas with subsequent improvement of liver fibrosis was recorded in the infected DFO treated group. This immunopathology was also associated with significant up regulation of Interlukine12 (IL12), Interferon gamma (IFN γ) and significant down regulation in interleukin4 (IL4), interleukin10 (IL10) in both serum and hepatic tissue in the infected DFO treated compared to other groups. Entirely, DFO succeeded in diminishing the growth, maturity and fecundity of S. mansoni with a subsequent improvement of hepatic pathology. As a result of the above findings, it can be concluded that DFO could be considered as a useful treatment against schistosomal infection.

Adjunctive therapy for severe malaria: a review and critical appraisal

BACKGROUND

Despite recent efforts and successes in reducing the malaria burden globally, this infection still accounts for an estimated 212 million clinical cases, 2 million severe malaria cases, and approximately 429,000 deaths annually. Even with the routine use of effective anti-malarial drugs, the case fatality rate for severe malaria remains unacceptably high, with cerebral malaria being one of the most life-threatening complications. Up to one-third of cerebral malaria survivors are left with long-term cognitive and neurological deficits. From a population point of view, the decrease of malaria transmission may jeopardize the development of naturally acquired immunity against the infection, leading to fewer total cases, but potentially an increase in severe cases. The pathophysiology of severe and cerebral malaria is not completely understood, but both parasite and host determinants contribute to its onset and outcomes. Adjunctive therapy, based on modulating the host response to infection, could help to improve the outcomes achieved with specific anti-malarial therapy.

RESULTS AND CONCLUSIONS

In the last decades, several interventions targeting different pathways have been tested. However, none of these strategies have demonstrated clear beneficial effects, and some have shown deleterious outcomes. This review aims to summarize evidence from clinical trials testing different adjunctive therapy for severe and cerebral malaria in humans. It also highlights some preclinical studies which have evaluated novel strategies and other candidate therapeutics that may be evaluated in future clinical trials.

Mechanisms of murine cerebral malaria: Multimodal imaging of altered cerebral metabolism and protein oxidation at hemorrhage sites

Using a multimodal biospectroscopic approach, we settle several long-standing controversies over the molecular mechanisms that lead to brain damage in cerebral malaria, which is a major health concern in developing countries because of high levels of mortality and permanent brain damage. Our results provide the first conclusive evidence that important components of the pathology of cerebral malaria include peroxidative stress and protein oxidation within cerebellar gray matter, which are colocalized with elevated nonheme iron at the site of microhemorrhage. Such information could not be obtained previously from routine imaging methods, such as electron microscopy, fluorescence, and optical microscopy in combination with immunocytochemistry, or from bulk assays, where the level of spatial information is restricted to the minimum size of tissue that can be dissected. We describe the novel combination of chemical probe-free, multimodal imaging to quantify molecular markers of disturbed energy metabolism and peroxidative stress, which were used to provide new insights into understanding the pathogenesis of cerebral malaria. In addition to these mechanistic insights, the approach described acts as a template for the future use of multimodal biospectroscopy for understanding the molecular processes involved in a range of clinically important acute and chronic (neurodegenerative) brain diseases to improve treatment strategies.

The Iron age of host-microbe interactions

Microbes exert a major impact on human health and disease by either promoting or disrupting homeostasis, in the latter instance leading to the development of infectious diseases. Such disparate outcomes are driven by the ever-evolving genetic diversity of microbes and the countervailing host responses that minimize their pathogenic impact. Host defense strategies that limit microbial pathogenicity include resistance mechanisms that exert a negative impact on microbes, and disease tolerance mechanisms that sustain host homeostasis without interfering directly with microbes. While genetically distinct, these host defense strategies are functionally integrated, via mechanisms that remain incompletely defined. Here, we explore the general principles via which host adaptive responses regulating iron (Fe) metabolism impact on resistance and disease tolerance to infection.

ZIPCO, a putative metal ion transporter, is crucial for Plasmodium liver-stage development

The malaria parasite, Plasmodium, requires iron for growth, but how it imports iron remains unknown. We characterize here a protein that belongs to the ZIP (Zrt-, Irt-like Protein) family of metal ion transport proteins and have named ZIP domain-containing protein (ZIPCO). Inactivation of the ZIPCO-encoding gene in Plasmodium berghei, while not affecting the parasite's ability to multiply in mouse blood and to infect mosquitoes, greatly impairs its capacity to develop inside hepatocytes. Iron/zinc supplementation and depletion experiments suggest that ZIPCO is required for parasite utilization of iron and possibly zinc, consistent with its predicted function as a metal transporter. This is the first report of a ZIP protein having a crucial role in Plasmodium liver-stage development, as well as the first metal ion transporter identified in Plasmodium pre-erythrocytic stages. Because of the drastic dependence on iron of Plasmodium growth, ZIPCO and related proteins might constitute attractive drug targets to fight against malaria.

Management of severe paediatric malaria in resource-limited settings

Over 90% of the world's severe and fatal Plasmodium falciparum malaria is estimated to affect young children in sub-Sahara Africa, where it remains a common cause of hospital admission and inpatient mortality. Few children will ever be managed on high dependency or intensive care units and, therefore, rely on simple supportive treatments and parenteral anti-malarials. There has been some progress on defining best practice for antimalarial treatment with the publication of the AQUAMAT trial in 2010, involving 5,425 children at 11 centres across 9 African countries, showing that in artesunate-treated children, the relative risk of death was 22.5% (95% confidence interval (CI) 8.1 to 36.9) lower than in those receiving quinine. Human trials of supportive therapies carried out on the basis of pathophysiology studies, have so far made little progress on reducing mortality; despite appearing to reduce morbidity endpoints, more often than not they have led to an excess of adverse outcomes. This review highlights the spectrum of complications in African children with severe malaria, the therapeutic challenges of managing these in resource-poor settings and examines in-depth the results from clinical trials with a view to identifying the treatment priorities and a future research agenda.

Iron at the interface of immunity and infection

Both, mammalian cells and microbes have an essential need for iron, which is required for many metabolic processes and for microbial pathogenicity. In addition, cross-regulatory interactions between iron homeostasis and immune function are evident. Cytokines and the acute phase protein hepcidin affect iron homeostasis leading to the retention of the metal within macrophages and hypoferremia. This is considered to result from a defense mechanism of the body to limit the availability of iron for extracellular pathogens while on the other hand the reduction of circulating iron results in the development of anemia of inflammation. Opposite, iron and the erythropoiesis inducing hormone erythropoietin affect innate immune responses by influencing interferon-gamma (IFN-γ) mediated (iron) or NF-kB inducible (erythropoietin) immune effector pathways in macrophages. Thus, macrophages loaded with iron lose their ability to kill intracellular pathogens via IFN-γ mediated effector pathways such as nitric oxide (NO) formation. Accordingly, macrophages invaded by the intracellular bacterium Salmonella enterica serovar Typhimurium increase the expression of the iron export protein ferroportin thereby reducing the availability of iron for intramacrophage bacteria while on the other side strengthening anti-microbial macrophage effector pathways via increased formation of NO or TNF-α. In addition, certain innate resistance genes such as natural resistance associated macrophage protein function (Nramp1) or lipocalin-2 exert part of their antimicrobial activity by controlling host and/or microbial iron homeostasis. Consequently, pharmacological or dietary modification of cellular iron trafficking enhances host resistance to intracellular pathogens but may increase susceptibility to microbes in the extracellular compartment and vice versa. Thus, the control over iron homeostasis is a central battlefield in host–pathogen interplay influencing the course of an infectious disease in favor of either the mammalian host or the pathogenic invader.

Managing malaria in the intensive care unit

The number of people travelling to malaria-endemic countries continues to increase, and malaria remains the commonest cause of serious imported infection in non-endemic areas. Severe malaria, mostly caused by Plasmodium falciparum, often requires intensive care unit (ICU) admission and can be complicated by cerebral malaria, respiratory distress, acute kidney injury, bleeding complications, and co-infection. The mortality from imported malaria remains significant. This article reviews the manifestations, complications and principles of management of severe malaria as relevant to critical care clinicians, incorporating recent studies of anti-malarial and adjunctive treatment. Effective management of severe malaria includes prompt diagnosis and early institution of effective anti-malarial therapy, recognition of complications, and appropriate supportive management in an ICU. All cases should be discussed with a specialist unit and transfer of the patient considered.

The association between malaria and iron status or supplementation in pregnancy: a systematic review and meta-analysis

Introduction

Malaria prevention and iron supplementation are associated with improved maternal and infant outcomes. However, evidence from studies in children suggests iron may adversely modify the risk of malaria. We reviewed the evidence in pregnancy of the association between malaria and markers of iron status, iron supplementation or parenteral treatment.

Methods and Findings

We searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, the Global Health Library, and the Malaria in Pregnancy library to identify studies that investigated the association between iron status, iron treatment or supplementation during pregnancy and malaria. Thirty one studies contributed to the analysis; 3 experimental and 28 observational studies. Iron supplementation was not associated with an increased risk of P. falciparum malaria during pregnancy or delivery in Africa (summary Relative Risk = 0.89, 95% Confidence Interval (CI) 0.66–1.20, I² = 78.8%, 5 studies). One study in Asia reported an increased risk of P. vivax within 30 days of iron supplementation (e.g. adjusted Hazard Ratio = 1.75, 95% CI 1.14–2.70 for 1–15 days), but not after 60 days. Iron deficiency (based on ferritin and C-reactive protein) was associated with lower odds for malaria infection (summary Odds Ratio = 0.35, 0.24–0.51, I² = 59.2%, 5 studies). With the exception of the acute phase protein ferritin, biomarkers of iron deficiency were generally not associated with malaria infection.

Conclusions

Iron supplementation was associated with a temporal increase in P vivax, but not with an increased risk of P. falciparum; however, data are insufficient to rule out the potential for an increased risk of P. falciparum. Iron deficiency was associated with a decreased malaria risk in pregnancy only when measured with ferritin. Until there is more evidence, it is prudent to provide iron in combination with malaria prevention during pregnancy.

Management of severe malaria in the intensive care unit

Severe malaria is a medical emergency requiring early intervention to prevent death. This article highlights key aspects of the management of severe malaria syndromes in the intensive care unit, with a focus on individual case management of imported malaria. Key differences in the presentation, management, and outcomes of severe malaria by endemicity and by age group are emphasized. In all groups with severe malaria, intravenous artesunate is the antimalarial agent of choice. This article discusses specific antimalarial therapies, optimal supportive management strategies, differences from strategies for bacterial sepsis, and trials of adjunctive therapy for severe malaria in humans.

CD19(+) B cells confer protection against experimental cerebral malaria in semi-immune rodent model

In African endemic area, adults are less vulnerable to cerebral malaria than children probably because of acquired partial immunity or semi-immune status. Here, we developed an experimental cerebral malaria (ECM) model for semi-immune mice. C57BL/6 (B6) mice underwent one, two and three cycles of infection and radical treatment (1-cure, 2-cure and 3-cure, respectively) before being finally challenged with 10⁴Plasmodium berghei ANKA without treatment. Our results showed that 100% of naïve (0-cure), 67% of 1-cure, 37% of 2-cure and none of 3-cure mice succumbed to ECM within 10 days post challenge infection. In the protected 3-cure mice, significantly higher levels of plasma IL-10 and lower levels of IFN-γ than the others on day 7 post challenge infection were observed. Major increased lymphocyte subset of IL-10 positive cells in 3-cure mice was CD5(−)CD19(+) B cells. Passive transfer of splenic CD19(+) cells from 3-cure mice protected naïve mice from ECM. Additionally, aged 3-cure mice were also protected from ECM 12 and 20 months after the last challenge infection. In conclusion, mice became completely resistant to ECM after three exposures to malaria. CD19(+) B cells are determinants in protective mechanism of semi-immune mice against ECM possibly via modulatory IL-10 for pathogenic IFN-γ production.

Parasite maturation and host serum iron influence the labile iron pool of erythrocyte stage Plasmodium falciparum

Iron is a critical and tightly regulated nutrient for both the malaria parasite and its human host. The importance of the relationship between host iron and the parasite has been underscored recently by studies showing that host iron supplementation may increase the risk of falciparum malaria. It is unclear what host iron sources the parasite is able to access. We developed a flow cytometry-based method for measuring the labile iron pool (LIP) of parasitized erythrocytes using the nucleic acid dye STYO 61 and the iron sensitive dye, calcein acetoxymethyl ester (CA-AM). This new approach enabled us to measure the LIP of P. falciparum through the course of its erythrocytic life cycle and in response to the addition of host serum iron sources. We found that the LIP increases as the malaria parasite develops from early ring to late schizont stage, and that the addition of either transferrin or ferric citrate to culture media increases the LIP of trophozoites. Our method for detecting the LIP within malaria parasitized RBCs provides evidence that the parasite is able to access serum iron sources as part of the host vs. parasite arms race for iron.

Oral Administration of Ferrous Sulfate, but not of Iron Polymaltose or Sodium Iron Ethylenediaminetetraacetic Acid (NaFeEDTA), Results in a Substantial Increase of Non-Transferrin-Bound Iron in Healthy Iron-Adequate Men

Background

Oral iron supplementation with ferrous sulfate (FeSO4) at dosage levels suggested by the international guidelines poses a safety hazard to young children with malaria. Exposure to loosely bound iron in the circulation has been advanced as a potential factor.

Objective

To evaluate the kinetics of circulating concentrations of plasma iron and non-transferrin-bound iron (NTBI) in response to oral iron administration in healthy adults.

Methods

Plasma samples were collected at 90-minute intervals over a period of 270 minutes from 10 healthy Guatemalan men after oral administration of water or 100 mg of iron from each of three iron compounds: FeSO4, sodium iron ethylenediaminetetraacetic acid (NaFeEDTA), and iron polymaltose. The four tests were administered in an individually randomized sequence. Serum iron concentration was measured spectrophotometrically by the ferrozine method, and NTBI concentration was measured by a fluorometric competitive binding assay. The kinetic response and the maximal and cumulative changes in circulating concentrations of the biomarkers of interest were compared.

Results

Serum iron and NTBI responses to oral administration of FeSO4 were significantly greater than responses to plain water or the other two iron compounds. NTBI concentrations after NaFeEDTA or iron polymaltose ingestion were not different from those determined after water intake.

Conclusions

Administration of two iron compounds of proven bioavailability, but with complex absorption characteristics, is associated with a negligible NTBI response, potentially mitigating the safety concerns associated with iron supplementation in malarial areas.

Antimalarial iron chelator, FBS0701, shows asexual and gametocyte Plasmodium falciparum activity and single oral dose cure in a murine malaria model

Iron chelators for the treatment of malaria have proven therapeutic activity in vitro and in vivo in both humans and mice, but their clinical use is limited by the unsuitable absorption and pharmacokinetic properties of the few available iron chelators. FBS0701, (S)3"-(HO)-desazadesferrithiocin-polyether [DADFT-PE], is an oral iron chelator currently in Phase 2 human studies for the treatment of transfusional iron overload. The drug has very favorable absorption and pharmacokinetic properties allowing for once-daily use to deplete circulating free iron with human plasma concentrations in the high µM range. Here we show that FBS0701 has inhibition concentration 50% (IC(50)) of 6 µM for Plasmodium falciparum in contrast to the IC(50) for deferiprone and deferoxamine at 15 and 30 µM respectively. In combination, FBS0701 interfered with artemisinin parasite inhibition and was additive with chloroquine or quinine parasite inhibition. FBS0701 killed early stage P. falciparum gametocytes. In the P. berghei Thompson suppression test, a single dose of 100 mg/kg reduced day three parasitemia and prolonged survival, but did not cure mice. Treatment with a single oral dose of 100 mg/kg one day after infection with 10 million lethal P. yoelii 17XL cured all the mice. Pretreatment of mice with a single oral dose of FBS0701 seven days or one day before resulted in the cure of some mice. Plasma exposures and other pharmacokinetics parameters in mice of the 100 mg/kg dose are similar to a 3 mg/kg dose in humans. In conclusion, FBS0701 demonstrates a single oral dose cure of the lethal P. yoelii model. Significantly, this effect persists after the chelator has cleared from plasma. FBS0701 was demonstrated to remove labile iron from erythrocytes as well as enter erythrocytes to chelate iron. FBS0701 may find clinically utility as monotherapy, a malarial prophylactic or, more likely, in combination with other antimalarials.

HMOX1 gene promoter alleles and high HO-1 levels are associated with severe malaria in Gambian children

Heme oxygenase 1 (HO-1) is an essential enzyme induced by heme and multiple stimuli associated with critical illness. In humans, polymorphisms in the HMOX1 gene promoter may influence the magnitude of HO-1 expression. In many diseases including murine malaria, HO-1 induction produces protective anti-inflammatory effects, but observations from patients suggest these may be limited to a narrow range of HO-1 induction, prompting us to investigate the role of HO-1 in malaria infection. In 307 Gambian children with either severe or uncomplicated P. falciparum malaria, we characterized the associations of HMOX1 promoter polymorphisms, HMOX1 mRNA inducibility, HO-1 protein levels in leucocytes (flow cytometry), and plasma (ELISA) with disease severity. The (GT)(n) repeat polymorphism in the HMOX1 promoter was associated with HMOX1 mRNA expression in white blood cells in vitro, and with severe disease and death, while high HO-1 levels were associated with severe disease. Neutrophils were the main HO-1-expressing cells in peripheral blood, and HMOX1 mRNA expression was upregulated by heme-moieties of lysed erythrocytes. We provide mechanistic evidence that induction of HMOX1 expression in neutrophils potentiates the respiratory burst, and propose this may be part of the causal pathway explaining the association between short (GT)(n) repeats and increased disease severity in malaria and other critical illnesses. Our findings suggest a genetic predisposition to higher levels of HO-1 is associated with severe illness, and enhances the neutrophil burst leading to oxidative damage of endothelial cells. These add important information to the discussion about possible therapeutic manipulation of HO-1 in critically ill patients.

Iron deficiency protects against severe Plasmodium falciparum malaria and death in young children

BACKGROUND

Iron supplementation may increase malaria morbidity and mortality, but the effect of naturally occurring variation in iron status on malaria risk is not well studied.

METHODS

A total of 785 Tanzanian children living in an area of intense malaria transmission were enrolled at birth, and intensively monitored for parasitemia and illness including malaria for up to 3 years, with an average of 47 blood smears. We assayed plasma samples collected at routine healthy-child visits, and evaluated the impact of iron deficiency (ID) on future malaria outcomes and mortality.

RESULTS

ID at routine, well-child visits significantly decreased the odds of subsequent parasitemia (23% decrease, P < .001) and subsequent severe malaria (38% decrease, P = .04). ID was also associated with 60% lower all-cause mortality (P = .04) and 66% lower malaria-associated mortality (P = .11). When sick visits as well as routine healthy-child visits are included in analyses (average of 3 iron status assays/child), ID reduced the prevalence of parasitemia (6.6-fold), hyperparasitemia (24.0-fold), and severe malaria (4.0-fold) at the time of sample collection (all P < .001).

CONCLUSIONS

Malaria risk is influenced by physiologic iron status, and therefore iron supplementation may have adverse effects even among children with ID. Future interventional studies should assess whether treatment for ID coupled with effective malaria control can mitigate the risks of iron supplementation for children in areas of malaria transmission.

Superinfection in malaria: Plasmodium shows its iron will

After the bite of a malaria-infected mosquito, the Plasmodium sporozoite infects liver cells and produces thousands of merozoites, which then infect red blood cells, causing malaria. In malaria-endemic areas, several hundred infected mosquitoes can bite an individual each year, increasing the risk of superinfection. However, in infants that are yet to acquire immunity, superinfections are infrequent. We have recently shown that blood-stage parasitaemia, above a minimum threshold, impairs the growth of a subsequent sporozoite infection of liver cells. Blood-stage parasites stimulate the production of the host iron-regulatory factor hepcidin, which redistributes iron away from hepatocytes, reducing the development of the iron-dependent liver stage. This could explain why Plasmodium superinfection is not often found in young nonimmune children. Here, we discuss the impact that such protection from superinfection might have in epidemiological settings or in programmes for controlling malaria, as well as how the induction of hepcidin and redistribution of iron might influence anaemia and the outcome of non-Plasmodium co-infections.

Iron metabolism and the innate immune response to infection

Host antimicrobial mechanisms reduce iron availability to pathogens. Iron proteins influencing the innate immune response include hepcidin, lactoferrin, siderocalin, haptoglobin, hemopexin, Nramp1, ferroportin and the transferrin receptor. Numerous global health threats are influenced by iron status and provide examples of our growing understanding of the connections between infection and iron metabolism.

Nifedipine affects the course of Salmonella enterica serovar Typhimurium infection by modulating macrophage iron homeostasis

BACKGROUND

Iron overload can adversely influence the course of infection by increasing microbial replication and suppressing antimicrobial immune effector pathways. Recently, we have shown that the calcium channel blocker nifedipine can mobilize tissue iron in mouse models of iron overload. We therefore investigated whether nifedipine treatment affects the course of infection with intracellular bacteria via modulation of iron homeostasis.

METHODS

The effect of nifedipine on intramacrophage replication of bacteria and modulation of cellular iron homeostasis was investigated in the murine macrophage cell line RAW264.7, and the impact of nifedipine treatment on the course of systemic infection was investigated in C57BL/6 mice in vivo.

RESULTS

In RAW264.7 cells, nifedipine treatment significantly reduced intracellular bacterial survival of Salmonella enterica serovar Typhimurium and Chlamydophila pneumoniae. This could be attributed to the induction of the iron exporter ferroportin 1, which limited the availability of iron for intracellular Salmonella. When C57BL/6 mice were infected intraperitoneally with Salmonella and subsequently injected with nifedipine for 3 consecutive days, bacterial counts in livers and spleens were significantly reduced and survival of the mice significantly was prolonged compared with solvent-treated littermates. Nifedipine treatment increased expression of ferroportin 1 in the spleen, whereas splenic levels of the iron storage protein ferritin and serum iron concentrations were reduced.

CONCLUSIONS

Our data provide evidence for a novel mechanism whereby nifedipine enhances host resistance to intracellular pathogens via limitation of iron availability.

Iron as a target of chemoprevention for longevity in humans

Iron is universally abundant and no life can exist without it. However, iron levels should be maintained within a narrow range. Iron deficiency causes anaemia, whereas excessive iron increases cancer risk, presumably by free radical generation. Several pathological conditions such as genetic haemochromatosis, chronic viral hepatitis B and C, conditions related to asbestos fibre exposure and ovarian endometriosis have been recognized as iron overload-associated conditions that also increase human cancer risks. Iron's carcinogenicity has been documented in animal experiments. Surprisingly, these studies have revealed that the homozygous deletion of CDKN2A/2B is a major hallmark of iron-induced carcinogenesis. Recently, the hormonal regulation of iron metabolism has been elucidated. A commonly hypothesized mechanism may be the lack of any iron disposal pathway other than for bleeding and a mechanism of iron re-uptake as catechol chelate has been discovered. Iron overload in neurons via the ferroportin block may play a role in Alzheimer's disease. Furthermore, a recent epidemiological study reported that iron reduction by phlebotomy was associated with decreased cancer risks in a general population. Given that the required amounts of iron decrease during ageing, the fine control of body iron stores would be a wise strategy for chemoprevention of several diseases.

Trypanosoma cruzi: desferrioxamine decreases mortality and parasitemia in infected mice through a trypanostatic effect

Desferrioxamine (DFO) is a potent iron chelator that is also known to modulate inflammation and act as an efficient antioxidant under normal conditions and under oxidative stress. Many in vitro and in vivo studies have shown the efficacy of DFO in the treatment of viral, bacterial and protozoan infections. DFO is known to reduce the intensity of Trypanosoma cruzi infections in mice even during a course of therapy that is not effective in maintaining anaemia or low iron levels. To further clarify these findings, we investigated the action of DFO on mouse T. cruzi infection outcomes and the direct impact of DFO on parasites. Infected animals treated with DFO (5 mg/animal/day) for 35 days, beginning 14 days prior to infection, presented lower parasitemia and lower cumulative mortality rate. No significant effect was observed on iron metabolism markers, erythrograms, leukograms or lymphocyte subsets. In the rapid method for testing in vivo T. cruzi susceptibility, DFO also induced lower parasitemia. In regard to its direct impact on parasites, DFO slightly inhibited the growth of amastigotes and trypomastigotes in fibroblast culture. Trypan blue staining showed no effects of DFO on parasite viability, and only minor apoptosis in trypomastigotes was observed. Nevertheless, a clear decrease in parasite mobility was detected. In conclusion, the beneficial actions of DFO on mice T. cruzi infection seem to be independent of host iron metabolism and free of significant haematological side effects. Through direct action on the parasite, DFO has more effective trypanostatic than trypanocidal properties.

In vitro antimalarial activity of ICL670: a further proof of the correlation between inhibition of β-hematin formation and of peroxidative degradation of hemin

Iron chelators such as deferiprone, deferoxamine (DFO) and ICL670 (deferasirox) have previously been shown to display in vitro and/or in vivo antimalarial activities. To gain further insight in their antimalarial mechanism of action, their activities on inhibition of β-hematin formation and on both peroxidative and glutathione (GSH)-mediated degradation of hemin were investigated. Neither deferiprone nor DFO were able to inhibit β-hematin formation while ICL670 activity nearly matched that of chloroquine (CQ). Peroxidative degradation of hemin was also only strongly inhibited by both CQ and ICL670, the latter being significantly more efficient at pH 5.2. All iron chelators displayed minor, if any, inhibitory activity on GSH-mediated degradation of hemin. Discrepancies in the results obtained for the three iron chelators show that iron chelation is not the main driving force behind interference with heme degradation. Deferiprone, DFO and ICL670 share little structural community but both ICL670 and antimalarial ursolic acid derivatives (previously shown to block β-hematin formation and the peroxidative degradation of hemin) have hydrophobic groups and hydroxyphenyl moieties. These similarities in structures and activities further back up a possible two-step mechanism of action previously proposed for ursolic acid derivatives (Mullié et al., 2010) implying (1) stacking of an hydrophobic structure to hemin and (2) additive protection of hemin ferric iron from H(2)O(2) by hydroxyphenyl groups through steric hindrance and/or trapping of oxygen reactive species in the direct neighborhood of ferric iron. These peculiar antimalarial mechanisms of action for ICL670 warrant further investigations and development.

Adjunctive therapy for cerebral malaria and other severe forms of Plasmodium falciparum malaria

Severe malaria due to Plasmodium falciparum causes more than 800,000 deaths every year. Primary therapy with quinine or artesunate is generally effective in controlling P. falciparum parasitemia, but mortality from cerebral malaria and other forms of severe malaria remains unacceptably high. Long-term cognitive impairment is also common in children with cerebral malaria. Of the numerous adjunctive therapies for cerebral malaria and severe malaria studied over the past five decades, only one (albumin) was associated with a reduction in mortality. In this article, we review past and ongoing studies of adjunctive therapy, and examine the evidence of efficacy for newer therapies, including inhibitors of cytoadherence (e.g., levamisole), immune modulators (e.g., rosiglitazone), agents that increase nitric oxide levels (e.g., arginine) and neuroprotective agents (e.g., erythropoietin).

An extended-release formulation of desferrioxamine for subcutaneous administration

Desferrioxamine mesylate (DFO) remains the first line iron chelating agent. Since it has a short half-life and poor absorption through the gastrointestinal tract, DFO must be administered parenterally, usually by daily subcutaneous infusion administered over 8-12 h. The objective of this paper was the development of multivesicular liposome (depofoam) for the extended-release of DFO and study of iron excretion efficiency compared to the free form of DFO. Depofoam particles were characterized by their morphology, particle size, capture volume, and in vitro release. Also, in vivo activity of this formulation in iron overload rats was studied. The in vitro studies in 0.9% sodium chloride at 37 degrees C showed that the multivesicular liposomes released DFO slowly over several days without a rapid initial release, and 57% of DFO was released in 9 days. Administration of a single dose of 100 mg/kg of an optimized Depo-DFO formulation in an iron overload rats, as a single bolus subcutaneous injection, led to significant elevation of urinary iron excretion at the first day that were maintained at levels of more than 110 microg/kg for 3 days. Administration of the unencapsulated DFO at the same dose resulted in elevation of urinary iron excretion in the first day (approximately 73% amount of iron excretion by Depo-DFO) followed by a quick decline to base line levels in the second day. The total urinary iron excreted by Depo-DFO is 3-times greater than that elicited by DFO. In conclusion, Depo-DFO appears to have potential usefulness as an extended-release formulation of DFO.

Diagnosis and management of the neurological complications of falciparum malaria

Malaria is a major public health problem in the developing world owing to its high rates of morbidity and mortality. Of all the malarial parasites that infect humans, Plasmodium falciparum is most commonly associated with neurological complications, which manifest as agitation, psychosis, seizures, impaired consciousness and coma (cerebral malaria). Cerebral malaria is the most severe neurological complication; the condition is associated with mortality of 15-20%, and a substantial proportion of individuals with this condition develop neurocognitive sequelae. In this Review, we describe the various neurological complications encountered in malaria, discuss the underlying pathogenesis, and outline current management strategies for these complications. Furthermore, we discuss the role of adjunctive therapies in improving outcome.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Mechanism of iron toxicity

The subtle balance between proinflammatory and antiinflammatory cytokines plays an important role in determining the severity of the inflammatory reaction and in the anomalous iron handling associated with infection. Conversely, iron deficiency per se appears to limit the severity of the inflammatory response. All of these considerations are at present highly speculative and in need of further experimental and epidemiologic support. If confirmed, the beneficial biological effects of iron depletion may have a defensive role in inflammation and may be perturbed by the nonselective administration of iron to iron-replete patients who would not benefit from such treatment in the first place. In view of the importance of non-transferrin-bound plasma iron (NTBI) in iron toxicity and its rapid cellular uptake, it may play an important role in the harmful effects of iron in infection, and this is illustrated by the infectious complications of parenteral iron therapy in tropical countries.

High levels of erythropoietin are associated with protection against neurological sequelae in African children with cerebral malaria

Cerebral malaria (CM) in children is associated with a high mortality and long-term neurocognitive sequelae. Both erythropoietin (Epo) and vascular endothelial growth factor (VEGF) have been shown to be neuroprotective. We hypothesized that high plasma and cerebrospinal fluid (CSF) levels of these cytokines would prevent neurological sequelae in children with CM. We measured Epo, VEGF, and tumor necrosis factor in paired samples of plasma and CSF of Kenyan children admitted with CM. Logistic regression models were used to identify risk and protective factors associated with the development of neurological sequelae. Children with CM (n = 124) were categorized into three groups: 76 without sequelae, 32 with sequelae, and 16 who died. Conditional logistic regression analysis matching the 32 patients with CM and neurological sequelae to 64 patients with CM without sequelae stratified for hemoglobin level estimated that plasma Epo (>200 units/liter) was associated with >80% reduction in the risk of developing neurological sequelae [adjusted odds ratio (OR) 0.18; 95% C.I. 0.05-0.93; P = 0.041]. Admission with profound coma (adjusted OR 5.47; 95% C.I. 1.45-20.67; P = 0.012) and convulsions after admission (adjusted OR 16.35; 95% C.I. 2.94-90.79; P = 0.001) were also independently associated with neurological sequelae. High levels of Epo were associated with reduced risk of neurological sequelae in children with CM. The age-dependent Epo response to anemia and the age-dependent protective effect may influence the clinical epidemiology of CM. These data support further study of Epo as an adjuvant therapy in CM.

Nutritional iron deficiency: an evolutionary perspective

Iron deficiency, with or without iron-deficiency anemia, is so ubiquitous that it affects all populations of the world irrespective of race, culture, or ethnic background. Despite all the latest advances in modern medicine, improved nutrition, and the ready availability of cheap oral iron, there is still no good explanation for the widespread persistence of iron deficiency. It is possible that the iron deficiency phenotype is very prevalent because of many factors other than the commonly cited causes such as a decreased availability or an increased utilization of iron. Several thousand years ago, human culture changed profoundly with the agrarian revolution, when humans turned to agriculture. Their diet became iron deficient and new epidemic infections emerged due to crowding and lifestyle changes. There is convincing evidence that iron deficiency protects against many infectious diseases such as malaria, plague, and tuberculosis as shown by diverse medical, historical, and anthropologic studies. Thus, this change of diet increased the frequency of iron deficiency, and epidemic infections exerted a selection pressure under which the iron deficiency phenotype survived better. Multiple evolutionary factors have contributed in making iron deficiency a successful phenotype. We analyze some of the recent findings of iron metabolism, the theories explaining excessive menstruation in human primates, the unexplained relative paucity of hemochromatosis genes, the former medical practice of "blood-letting," and other relevant historical data to fully understand the phenomenon of iron deficiency. We suggest that, due to a long evolutionary persistence of iron deficiency, efforts at its prevention will take a long time to be effective.

Trypanosoma cruzi: treatment with the iron chelator desferrioxamine reduces parasitemia and mortality in experimentally infected mice

The effects of prolonged treatment with iron chelator (desferrioxamine) on the development of infection in mice inoculated with Y Trypanosoma cruzi were determined. Infected/treated mice presented lower levels of parasitemia and reduced mortality rate compared with infected/non-treated animals. The five out of twenty infected/treated mice that survived the acute phase of infection showed negative hemoculture and positive ELISA in the acute and chronic phases and positive PCR in the acute phase: in the chronic phase, three of the animals presented negative PCR. The single surviving infected/non-treated animal exhibited positive hemoculture, PCR and ELISA in both phases of infection. Infected groups presented lower levels of iron in the liver compared with treated/non-infected or non-treated/non-infected animals. The serum iron levels of the infected/non-treated group were higher on the 21st day post-infection in comparison with control and infected/treated groups. These results suggest that decrease of iron in the host leads to T. cruzi infection attenuation.

Bioavailable iron and heme metabolism in Plasmodium falciparum

Iron metabolism is essential for cell function and potentially toxic because iron can catalyze oxygen radical production. Malaria-attributable anemia and iron deficiency anemia coincide as being treatable diseases in the developing world. In absolute amounts, more than 95% of Plasmodium metal biochemistry occurs in the acidic digestive vacuole where heme released from hemoglobin catabolism forms heme crystals. The antimalarial quinolines interfere with crystallization. Despite the completion of the Plasmodium genome, many 'gene gaps' exist in components of the metal pathways described in mammalian or yeast cells. Present evidence suggests that parasite bioavailable iron originates from a labile erythrocyte cytosolic pool rather than from abundant heme iron. Indeed the parasite has to make its own heme within two separate organelles, the mitochondrion and the apicomplast. Paradoxically, despite the abundance of iron within the erythrocyte, iron chelators are cytocidal to the Plasmodium parasite. Hemozoin has become a sensitive biomarker for laser desorption mass spectrometry detection of Plasmodium infection in both mice and humans.

A review of the quality of randomized clinical trials of adjunctive therapy for the treatment of cerebral malaria

BACKGROUND

Randomized controlled clinical trials (RCTs) of adjunctive treatment to reduce the high-mortality associated with cerebral malaria (CM) have so far failed to show any benefit. This may be due in part to improperly designed and/or conducted trials. Therefore a systematic review of quality of RCTs for the treatment of CM with mortality as either primary or secondary outcome published between 1980 and 2000, was conducted.

METHODS

RCTs from the peer-reviewed literature using electronic searches. Methodological quality was assessed using an individual component approach (adequacy of concealment of allocation schedule, generation of allocation sequence, double blinding and analysis of participant as randomized). Sample sizes were recalculated for the ability of reviewed trials to detect 25% and 50% reductions in mortality.

RESULTS

Nine trials satisfied the inclusion criteria and were reviewed. Only two had sufficient power to detect a 50% reduction in mortality, and none could detect a 25% reduction. All the trials had inadequate methodological quality in one or more of the components, although in two trials these deficiencies were few.

CONCLUSION

There is a need for researchers and donors to ensure proper planning and implementation of RCTs in developing countries. In CM, demonstration of worthwhile reduction in mortality by a single intervention will require a large number of subjects, which a single centre may not be able to recruit.