Leishmania chagasi: effect of the iron deficiency on the infection in BALB/c mice

Targeting and activation of macrophages in leishmaniasis. A focus on iron oxide nanoparticles

Macrophages play a pivotal role as host cells for Leishmania parasites, displaying a notable functional adaptability ranging from the proinflammatory, leishmanicidal M1 phenotype to the anti-inflammatory, parasite-permissive M2 phenotype. While macrophages can potentially eradicate amastigotes through appropriate activation, Leishmania employs diverse strategies to thwart this activation and redirect macrophages toward an M2 phenotype, facilitating its survival and replication. Additionally, a competition for iron between the two entities exits, as iron is vital for both and is also implicated in macrophage defensive oxidative mechanisms and modulation of their phenotype. This review explores the intricate interplay between macrophages, Leishmania, and iron. We focus the attention on the potential of iron oxide nanoparticles (IONPs) as a sort of immunotherapy to treat some leishmaniasis forms by reprogramming Leishmania-permissive M2 macrophages into antimicrobial M1 macrophages. Through the specific targeting of iron in macrophages, the use of IONPs emerges as a promising strategy to finely tune the parasite-host interaction, endowing macrophages with an augmented antimicrobial arsenal capable of efficiently eliminating these intrusive microbes.

The effects of intracellular iron availability on the outcome of Toxoplasma gondii infection in mice

Toxoplasma gondii (T. gondii) is a parasite that obtains the iron it needs for its own metabolism from the host-cell iron pool. In this work, we aimed to investigate if iron supplementation or deficiency affected the course of T. gondii infection. Eighty mice were divided into four groups, each with 20 animals: Group (I): Uninfected control group. Group (II): Infected control group: injected with Phosphate buffered saline. Group (III): Infected group: received iron sucrose treatment. Group (IV): Infected group: treated with deferoxamine. Quantitative PCR studies were performed on days 3 and 8 post-infection to detect the expression of iron metabolism genes (hamp and ferroprotin) and immune-histochemical analysis to study the percentage of TNF-α and TGF-β tissue expression. Iron supplementation induced progressions of infection evident by increased tissue expression of pro-inflammatory cytokine TNF-α and downregulation of TGF-β which is mostly linked to suppression of the inflammatory process caused by T. gondii. Increased expression of TGF-β and decreased expression of TNF-α was noticed when iron deprivation occurred. On day 3, we noticed increased expression in the hamp gene with iron supplementation while it decreases when the iron supply is low. On the contrary, iron deficiency increased ferroprotin gene expression whereas supplementing decreased it. On day 8, the level of expression of these genes returned to normal levels. These observations document the potential role of iron in controlling toxoplasmosis infection and indicate that the transcription of hamp and ferroprotin in T. gondii-infected cells appears to be regulated by a sophisticated indirect mechanism.

Genetic Iron Overload Hampers Development of Cutaneous Leishmaniasis in Mice

The survival, growth, and virulence of Leishmania spp., a group of protozoan parasites, depends on the proper access and regulation of iron. Macrophages, Leishmania's host cell, may divert iron traffic by reducing uptake or by increasing the efflux of iron via the exporter ferroportin. This parasite has adapted by inhibiting the synthesis and inducing the degradation of ferroportin. To study the role of iron in leishmaniasis, we employed Hjv^-/- mice, a model of hemochromatosis. The disruption of hemojuvelin (Hjv) abrogates the expression of the iron hormone hepcidin. This allows unrestricted iron entry into the plasma from ferroportin-expressing intestinal epithelial cells and tissue macrophages, resulting in systemic iron overload. Mice were injected with Leishmania major in hind footpads or intraperitoneally. Compared with wild-type controls, Hjv^-/- mice displayed transient delayed growth of L. major in hind footpads, with a significant difference in parasite burden 4 weeks post-infection. Following acute intraperitoneal exposure to L. major, Hjv^-/- peritoneal cells manifested increased expression of inflammatory cytokines and chemokines (Il1b, Tnfa, Cxcl2, and Ccl2). In response to infection with L. infantum, the causative agent of visceral leishmaniasis, Hjv^-/- and control mice developed similar liver and splenic parasite burden despite vastly different tissue iron content and ferroportin expression. Thus, genetic iron overload due to hemojuvelin deficiency appears to mitigate the early development of only cutaneous leishmaniasis.

Parasitological and immunological evaluation of a quinoline derivative salt incorporated into a polymeric micelle formulation against Leishmania infantum infection

Leishmaniasis is a parasitic disease caused by Leishmania protozoa, which presents a large spectrum of clinical manifestations. In the present study, a quinoline derivative salt named N-(2-((7-chloroquinolin-4-yl)amino)ethyl)-N-(prop-2-yn-1-yl)prop-2-yn-1-aminium chloride or QDS3 was in vitro and in vivo tested against L. infantum by means of its incorporation in Poloxamer 407-based polymeric micelles (QDS3/M). The in vitro antileishmanial activity of QDS3 and QDS3/M was investigated in L. infantum promastigotes, axenic amastigotes and infected macrophages. BALB/c mice were infected with L. infantum, and parasitological parameters were evaluated 1 and 15 days post-treatment by determining the parasite load by a limiting dilution assay, besides a quantitative PCR (qPCR) method. Immunological response was assessed based on production of cellular cytokines, as well as by quantification of nitrite levels and specific antibodies. In vitro results showed that QDS3 free or in micelles presented effective antileishmanial action against both parasite stages, being more effective in amastigotes. In vivo data showed that treatment using QDS3 or QDS3/M reduced the parasite load in the livers, spleens, draining lymph nodes (dLN) and bone marrows of the treated animals, 1 and 15 days after treatment, when compared to values found in the control groups. Additionally, treated mice developed a polarized Th1-type immune response, with higher levels of IL-12, IFN-γ, GM-CSF and nitrite, besides high production of specific IgG2a antibodies, when compared to the controls. Parasitological and immunological data obtained using the micellar composition were better than the others. In conclusion, QDS3, mainly when applied in a delivery adjuvant system, could be considered for future studies as therapeutic candidate against VL.

Flau-A, a naphthoquinone derivative, is a promising therapeutic candidate against visceral leishmaniasis: A preliminary study

Visceral leishmaniasis (VL) is a neglected tropical disease found in tropical and subtropical regions in the world. The therapeutics used for the treatment against disease presents problems, mainly related to drug toxicity, route of administration, high cost and/or by emergence of resistant strains. In this context, the search for alternative antileishmanial candidates is desirable. Recently, a naphthoquinone derivative namely 2-(2,3,4-tri-O-acetyl-6-deoxy-β-L-galactopyranosyloxy)-1,4-naphthoquinone or Flau-A showed an effective in vitro biological action against Leishmania infantum. In the present study, the efficacy of this naphthoquinone derivative was evaluated in an in vivo infection model. BALB/c mice (n = 12 per group) were infected and later received saline or were treated with empty micelles (B/Mic), free Flau-A or it incorporated in Poloxamer 407-based micelles (Flau-A/Mic). The products were administered subcutaneously in the infected animals, which were then euthanized one (n = 6 per group) and 15 (n = 6 per group) days post-therapy, when immunological and parasitological evaluations were performed. Results showed that animals treated with Flau-A or Flau-A/Mic produced significantly higher levels of antileishmanial IFN-γ, IL-12, TNF-α, GM-CSF, nitrite and IgG2a isotype antibody, when compared to data found in the control (saline and B/Mic) groups; which showed significantly higher levels of parasite-specific IL-4, IL-10 and IgG1 antibody. In addition, animals receiving free Flau-A or Flau-A/Mic presented also significant reductions in the parasite load in their spleens, livers, bone marrows and draining lymph nodes, when compared to the controls. A low hepatic and renal toxicity was also found. Overall, Flau-A/Mic showed better immunological and parasitological results, when compared to the use of free molecule. In conclusion, preliminary data suggest that this composition could be considered in future studies as promising therapeutic candidate against VL.

Protein regulation strategies of the mouse spleen in response to Babesia microti infection

BACKGROUND

Babesia is a protozoan parasite that infects red blood cells in some vertebrates. Some species of Babesia can induce zoonoses and cause considerable harm. As the largest immune organ in mammals, the spleen plays an important role in defending against Babesia infection. When infected with Babesia, the spleen is seriously injured but still actively initiates immunomodulatory responses.

METHODS

To explore the molecular mechanisms underlying the immune regulation and self-repair of the spleen in response to infection, this study used data-independent acquisition (DIA) quantitative proteomics to analyse changes in expression levels of global proteins and in phosphorylation modification in spleen tissue after Babesia microti infection in mice.

RESULTS

After mice were infected with B. microti, their spleens were seriously damaged. Using bioinformatics methods to analyse dynamic changes in a large number of proteins, we found that the spleen still initiated immune responses to combat the infection, with immune-related proteins playing an important role, including cathepsin D (CTSD), interferon-induced protein 44 (IFI44), interleukin-2 enhancer-binding factor 2 (ILF2), interleukin enhancer-binding factor 3 (ILF3) and signal transducer and activator of transcription 5A (STAT5A). In addition, some proteins related to iron metabolism were also involved in the repair of the spleen after B. microti infection, including serotransferrin, lactoferrin, transferrin receptor protein 1 (TfR1) and glutamate-cysteine ligase (GCL). At the same time, the expression and phosphorylation of proteins related to the growth and development of the spleen also changed, including protein kinase C-δ (PKC-δ), mitogen-activated protein kinase (MAPK) 3/1, growth factor receptor-bound protein 2 (Grb2) and P21-activated kinase 2 (PAK2).

CONCLUSIONS

Immune-related proteins, iron metabolism-related proteins and growth and development-related proteins play an important role in the regulation of spleen injury and maintenance of homeostasis. This study provides an important basis for the diagnosis and treatment of babesiosis.

Cytokines and metabolic regulation: A framework of bidirectional influences affecting Leishmania infection

Leishmania, a protozoan parasite inflicting the complex of diseases called Leishmaniases, resides and replicates as amastigotes within mammalian macrophages. As macrophages are metabolically highly active and can generate free radicals that can destroy this parasite, Leishmania also devise strategies to modulate the host cell metabolism. However, the metabolic changes can also be influenced by the anti-leishmanial immune response mediated by cytokines. This bidirectional, dynamic and complex metabolic coupling established between Leishmania and its host is the result of a long co-evolutionary process. Due to the continuous alterations imposed by the host microenvironment, such metabolic coupling continues to be dynamically regulated. The constant pursuit and competition for nutrients in the host-Leishmania duet alter the host metabolic pathways with major consequences for its nutritional reserves, eventually affecting the phenotype and functionality of the host cell. Altered phenotype and functions of macrophages are particularly relevant to immune cells, as perturbed metabolic fluxes can crucially affect the activation, differentiation, and functions of host immune cells. All these changes can deterministically direct the outcome of an infection. Cytokines and metabolic fluxes can bidirectionally influence each other through molecular sensors and regulators to dictate the final infection outcome. Our studies along with those from others have now identified the metabolic nodes that can be targeted for therapy.

Leishmania and its quest for iron: An update and overview

Parasites of genus Leishmania are the causative agents of complex neglected diseases called leishmaniasis and continue to be a significant health concern globally. Iron is a vital nutritional requirement for virtually all organisms, including pathogenic trypanosomatid parasites, and plays a crucial role in many facets of cellular metabolism as a cofactor of several enzymes. Iron acquisition is essential for the survival of parasites. Yet parasites are also vulnerable to the toxicity of iron and reactive oxygen species. The aim of this review is to provide an update on the current knowledge about iron acquisition and usage by Leishmania species. We have also discussed about host strategy to modulate iron availability and the strategies deployed by Leishmania parasites to overcome iron withholding defences and thus favour parasite growth within host macrophages. Since iron plays central roles in the host's response and parasite metabolism, a comprehensive understanding of the iron metabolism is beneficial to identify potential viable therapeutic opportunities against leishmaniasis.

Iron acquisition in Leishmania and its crucial role in infection

Iron is an essential cofactor for many basic metabolic pathways in pathogenic microbes and their hosts. It is also dangerous as it can catalyse the production of reactive free radicals. This dual character makes the host can either limit iron availability to invading microbes or exploit iron to induce toxicity to pathogens. Successful pathogens, including Leishmania species, must possess mechanisms to circumvent host's iron limitation and iron-induced toxicity in order to survive. In this review, we discuss the regulation of iron metabolism in the setting of infection and delineate the iron acquisition strategies used by Leishmania parasites and their subversions to host iron metabolism to overcome host's iron-related defences.

Iron in intracellular infection: to provide or to deprive?

Due to their chemical versatility, transition metals were incorporated as cofactors for several basic metabolic pathways in living organisms. This same characteristic makes them potentially harmful, since they can be engaged in deleterious reactions like Fenton chemistry. As such, organisms have evolved highly specialized mechanisms to supply their own metal needs while keeping their toxic potential in check. This dual character comes into play in host-pathogen interactions, given that the host can either deprive the pathogen of these key nutrients or exploit them to induce toxicity toward the invading agent. Iron stands as the prototypic example of how a metal can be used to limit the growth of pathogens by nutrient deprivation, a mechanism widely studied in Mycobacterium infections. However, the host can also take advantage of iron-induced toxicity to control pathogen proliferation, as observed in infections caused by Leishmania. Whether we may harness either of the two pathways for therapeutical purposes is still ill-defined. In this review, we discuss how modulation of the host iron availability impacts the course of infections, focusing on those caused by two relevant intracellular pathogens, Mycobacterium and Leishmania.

Iron overload favors the elimination of Leishmania infantum from mouse tissues through interaction with reactive oxygen and nitrogen species

Iron plays a central role in host-parasite interactions, since both intervenients need iron for survival and growth, but are sensitive to iron-mediated toxicity. The host's iron overload is often associated with susceptibility to infection. However, it has been previously reported that iron overload prevented the growth of Leishmania major, an agent of cutaneous leishmaniasis, in BALB/c mice. In order to further clarify the impact of iron modulation on the growth of Leishmania in vivo, we studied the effects of iron supplementation or deprivation on the growth of L. infantum, the causative agent of Mediterranean visceral leishmaniasis, in the mouse model. We found that dietary iron deficiency did not affect the protozoan growth, whereas iron overload decreased its replication in the liver and spleen of a susceptible mouse strain. The fact that the iron-induced inhibitory effect could not be seen in mice deficient in NADPH dependent oxidase or nitric oxide synthase 2 suggests that iron eliminates L. infantum in vivo through the interaction with reactive oxygen and nitrogen species. Iron overload did not significantly alter the mouse adaptive immune response against L. infantum. Furthermore, the inhibitory action of iron towards L. infantum was also observed, in a dose dependent manner, in axenic cultures of promastigotes and amastigotes. Importantly, high iron concentrations were needed to achieve such effects. In conclusion, externally added iron synergizes with the host's oxidative mechanisms of defense in eliminating L. infantum from mouse tissues. Additionally, the direct toxicity of iron against Leishmania suggests a potential use of this metal as a therapeutic tool or the further exploration of iron anti-parasitic mechanisms for the design of new drugs.

Leishmania are important vector-borne protozoan pathogens that cause different forms of disease, ranging from cutaneous self-healing lesions to life-threatening visceral infection. L. infantum is the most common species causing visceral leishmaniasis in Europe and the Mediterranean basin. Iron plays a critical role in host-pathogen interactions. Both the microorganism and its host need iron for growth. However, iron may promote the formation of toxic reactive oxygen species, which contribute to pathogen elimination, but also to host tissue pathology. We investigated the effect of manipulating host iron status on the outcome of L. infantum infection, using the mouse as an experimental model. We found that dietary iron deprivation had no effect on L. infantum growth, and iron-dextran injection decreased the multiplication of L. infantum in mouse organs. The fact that this anti-parasitic effect of iron was not observed in mice genetically deficient in superoxide and nitric oxide synthesis pathways indicates that iron is likely to act in synergy with reactive oxygen and nitrogen species produced by the host's macrophages. This work clearly shows that iron supplementation improves the host's capacity to eliminate L. infantum parasites and suggests that iron may be further explored as a therapeutic tool to fight this type of infection.

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.