Entamoeba histolytica secretes two haem-binding proteins to scavenge haem

Elucidation of iron homeostasis in Acanthamoeba castellanii

Acanthamoeba castellanii is a ubiquitously distributed amoeba that can be found in soil, dust, natural and tap water, air conditioners, hospitals, contact lenses and other environments. It is an amphizoic organism that can cause granulomatous amoebic encephalitis, an infrequent fatal disease of the central nervous system, and amoebic keratitis, a severe corneal infection that can lead to blindness. These diseases are extremely hard to treat; therefore, a more comprehensive understanding of this pathogen's metabolism is essential for revealing potential therapeutic targets. To propagate successfully in human tissues, the parasites must resist the iron depletion caused by nutritional immunity. The aim of our study is to elucidate the mechanisms underlying iron homeostasis in A. castellanii. Using a comparative whole-cell proteomic analysis of cells grown under different degrees of iron availability, we identified the primary proteins involved in Acanthamoeba iron acquisition. Our results suggest a two-step reductive mechanism of iron acquisition by a ferric reductase from the STEAP family and a divalent metal transporter from the NRAMP family. Both proteins are localized to the membranes of acidified digestive vacuoles where endocytosed medium and bacteria are trafficked. The expression levels of these proteins are significantly higher under iron-limited conditions, which allows Acanthamoeba to increase the efficiency of iron uptake despite the observed reduced pinocytosis rate. We propose that excessive iron gained while grown under iron-rich conditions is removed from the cytosol into the vacuoles by an iron transporter homologous to VIT/Ccc1 proteins. Additionally, we identified a novel protein that may participate in iron uptake regulation, the overexpression of which leads to increased iron acquisition.

The Mastigamoeba balamuthi Genome and the Nature of the Free-Living Ancestor of Entamoeba

The transition of free-living organisms to parasitic organisms is a mysterious process that occurs in all major eukaryotic lineages. Parasites display seemingly unique features associated with their pathogenicity; however, it is important to distinguish ancestral preconditions to parasitism from truly new parasite-specific functions. Here, we sequenced the genome and transcriptome of anaerobic free-living Mastigamoeba balamuthi and performed phylogenomic analysis of four related members of the Archamoebae, including Entamoeba histolytica, an important intestinal pathogen of humans. We aimed to trace gene histories throughout the adaptation of the aerobic ancestor of Archamoebae to anaerobiosis and throughout the transition from a free-living to a parasitic lifestyle. These events were associated with massive gene losses that, in parasitic lineages, resulted in a reduction in structural features, complete losses of some metabolic pathways, and a reduction in metabolic complexity. By reconstructing the features of the common ancestor of Archamoebae, we estimated preconditions for the evolution of parasitism in this lineage. The ancestor could apparently form chitinous cysts, possessed proteolytic enzyme machinery, compartmentalized the sulfate activation pathway in mitochondrion-related organelles, and possessed the components for anaerobic energy metabolism. After the split of Entamoebidae, this lineage gained genes encoding surface membrane proteins that are involved in host–parasite interactions. In contrast, gene gains identified in the M. balamuthi lineage were predominantly associated with polysaccharide catabolic processes. A phylogenetic analysis of acquired genes suggested an essential role of lateral gene transfer in parasite evolution (Entamoeba) and in adaptation to anaerobic aquatic sediments (Mastigamoeba).

Effect of magnetic field on the growth of the cultured Entamoeba histolytica isolated from patients in Palestine

Static magnetic field (SMF) is generated in vicinity of moving charge or current passing through conductor. In this study, we aimed to investigate the effect of SMF on the growth of the cultured Entamoeba histolytica (E. histolytica) trophozoites. Different SMF strengths with maximum value equals 30 mT (mT) was applied on the E.histolytica for different periods of times: 0 h, 24 h, 48 h, and 72 h. A modified diphasic liver infusion agar medium was used for culturing E. histolytica in vitro. The results showed the successful stabilization of culture of E. histolytica trophozoites. If we kept the sample for longer time, e. g. 14 days, the growth rate decreases to zero. When applying 10 mT and 15 mT SMF on the sample, it is found that the cultivated E. histolytica trophozoites dies after 4 and 2 days respectively. The experiments suggested that the SMF inhibited the growth and the propagation of E. histolytica cells. In addition, it completely killed all the cells in a short time interval which depend on the SMF strength. It is concluded that the SMFs inhibits the growth of E. histolytica and change the morphology of these cells. Thus, we recommend to use SMF as treatment to mitigate the growth of E. histolytica.

Supply and demand-heme synthesis, salvage and utilization by Apicomplexa

The Apicomplexa phylum groups important human and animal pathogens that cause severe diseases, encompassing malaria, toxoplasmosis, and cryptosporidiosis. In common with most organisms, apicomplexans rely on heme as cofactor for several enzymes, including cytochromes of the electron transport chain. This heme derives from de novo synthesis and/or the development of uptake mechanisms to scavenge heme from their host. Recent studies have revealed that heme synthesis is essential for Toxoplasma gondii tachyzoites, as well as for the mosquito and liver stages of Plasmodium spp. In contrast, the erythrocytic stages of the malaria parasites rely on scavenging heme from the host red blood cell. The unusual heme synthesis pathway in Apicomplexa spans three cellular compartments and comprises enzymes of distinct ancestral origin, providing promising drug targets. Remarkably given the requirement for heme, T. gondii can tolerate the loss of several heme synthesis enzymes at a high fitness cost, while the ferrochelatase is essential for survival. These findings indicate that T. gondii is capable of salvaging heme precursors from its host. Furthermore, heme is implicated in the activation of the key antimalarial drug artemisinin. Recent findings established that a reduction in heme availability corresponds to decreased sensitivity to artemisinin in T. gondii and Plasmodium falciparum, providing insights into the possible development of combination therapies to tackle apicomplexan parasites. This review describes the microeconomics of heme in Apicomplexa, from supply, either from de novo synthesis or scavenging, to demand by metabolic pathways, including the electron transport chain.

Adaptive iron utilization compensates for the lack of an inducible uptake system in Naegleria fowleri and represents a potential target for therapeutic intervention

Naegleria fowleri is a single-cell organism living in warm freshwater that can become a deadly human pathogen known as a brain-eating amoeba. The condition caused by N. fowleri, primary amoebic meningoencephalitis, is usually a fatal infection of the brain with rapid and severe onset. Iron is a common element on earth and a crucial cofactor for all living organisms. However, its bioavailable form can be scarce in certain niches, where it becomes a factor that limits growth. To obtain iron, many pathogens use different machineries to exploit an iron-withholding strategy that has evolved in mammals and is important to host-parasite interactions. The present study demonstrates the importance of iron in the biology of N. fowleri and explores the plausibility of exploiting iron as a potential target for therapeutic intervention. We used different biochemical and analytical methods to explore the effect of decreased iron availability on the cellular processes of the amoeba. We show that, under iron starvation, nonessential, iron-dependent, mostly cytosolic pathways in N. fowleri are downregulated, while the metal is utilized in the mitochondria to maintain vital respiratory processes. Surprisingly, N. fowleri fails to respond to acute shortages of iron by inducing the reductive iron uptake system that seems to be the main iron-obtaining strategy of the parasite. Our findings suggest that iron restriction may be used to slow the progression of infection, which may make the difference between life and death for patients.

Iron in parasitic protists – from uptake to storage and where we can interfere

A comprehensive review of iron metabolism in parasitic protists and its potential use as a drug target.

Iron-modulated virulence factors of Entamoeba histolytica

Entamoeba histolytica is a human parasite that causes amoebiasis, a disease that affects the colon and liver and is prevalent worldwide. This protozoan requires a high concentration of iron to survive and reproduce. Iron modulates the expression of parasite virulence factors, including hemoglobinases, hemoglobin-binding proteins and cysteine proteases, as well as proteins related to the amoebic cytoskeleton. This review summarizes the virulence factors that are affected by iron, resulting in upregulation or downregulation of E. histolytica genes. This review also discusses the functionality of iron in the mechanisms of pathogenesis.

Gene expression profiling in Entamoeba histolytica identifies key components in iron uptake and metabolism

Entamoeba histolytica is an ameboid parasite that causes colonic dysentery and liver abscesses in humans. The parasite encounters dramatic changes in iron concentration during its invasion of the host, with relatively low levels in the intestinal lumen and then relatively high levels in the blood and liver. The liver notably contains sources of iron; therefore, the parasite's ability to use these sources might be relevant to its survival in the liver and thus the pathogenesis of liver abscesses. The objective of the present study was to identify factors involved in iron uptake, use and storage in E. histolytica. We compared the respective transcriptomes of E. histolytica trophozoites grown in normal medium (containing around 169 µM iron), low-iron medium (around 123 µM iron), iron-deficient medium (around 91 µM iron), and iron-deficient medium replenished with hemoglobin. The differentially expressed genes included those coding for the ATP-binding cassette transporters and major facilitator transporters (which share homology with bacterial siderophores and heme transporters) and genes involved in heme biosynthesis and degradation. Iron deficiency was associated with increased transcription of genes encoding a subset of cell signaling molecules, some of which have previously been linked to adaptation to the intestinal environment and virulence. The present study is the first to have assessed the transcriptome of E. histolytica grown under various iron concentrations. Our results provide insights into the pathways involved in iron uptake and metabolism in this parasite.

Amebic liver abscess in northern region of Bangladesh: sociodemographic determinants and clinical outcomes

Background

Amebic liver abscess (ALA) is endemic in Bangladesh since historical age but its epidemiology and sociodemographic determinants are not well described in the literatures. This paper focuses on the endemicity, sociodemographic determinants and clinical outcomes of ALA patients from certain northern districts in Bangladesh. Ninety hospitalized ALA patients enrolled from 6 northern districts of Bangladesh during July 2008 to June 2010 were analyzed.

Findings

Clinical presentations of ALA was initially substantiated by ultrasound imaging and later confirmed by detection of small subunit rRNA gene of E. histolytica using a Real Time PCR. Structured questionnaire and data sheet were used to record sociodemographic characteristics, clinical presentations and outcomes. Patients were followed for immediate and late treatment outcomes up to 2 years since diagnosis. Northern districts those situated on the Ganges basin were noted as endemic areas. Male significantly outnumbered the female with a male to female ratio of 21:1 and majority of patients (58%) were in their 3rd and 4th decades. A significant (21%) number of patients were aborigines despite their ethnic minority as population under investigation and overall 68% belonged to low socioeconomic group. Habit of indigenous alcohol consumption was very high (78%) among ALA patients with overwhelming majority was illiterate (74.44%) and from rural population (70%). Fever with right hypochondriac pain of variable duration was the principal presenting complains. Gross fluid derangements including pleural effusion, edema and ascities were observed in 39% cases and 6% had rupture of abscess. All patients were treated with standard antimicrobial regimen and discharged with initial recovery. Recurrent attack was observed in 6% cases and 3 (3.33%) patients died during 2 years follow-up period. Complicated (37.78%) ALA patients showed significant Odds ratio (P < 0.05) for major sociodemographic determinants in comparison to non-complicated patients.

Conclusions

Amebic liver abscess is endemic in certain northern districts of Bangladesh especially on the Ganges basin with relatively high prevalence among aborigines. Rural habitat, ethnicity (Aborigine) and habit of indigenous alcohol consumption were found to be strong determinants, especially for complicated ALA, which were associated with different grades of morbidity and a few mortalities.

The frpB1 gene of Helicobacter pylori is regulated by iron and encodes a membrane protein capable of binding haem and haemoglobin

FrpB1 is a novel membrane protein of Helicobacter pylori that is capable of binding both haem and haemoglobin but consistently shows more affinity for haem. The mRNA levels of frpB1 were repressed by iron and lightly modulated by haem or haemoglobin. The overexpression of the frpB1 gene supported cellular growth when haem or haemoglobin were supplied as the only iron source. Three-dimensional modelling revealed the presence of motifs necessary to bind either haem or haemoglobin. Our overall results support the idea that FrpB1 is a membrane protein of H. pylori that allows this pathogen to survive in the human stomach.

Transferrin regulates mRNA levels of a gene involved in iron utilization in Entamoeba histolytica

Entamoeba histolytica is a human pathogen, which can survive using haemoglobin (Hb) as only iron supply. Two probable haemophores (Ehhmbp26 and Ehhmbp45) are involved in iron acquisition in this parasite. However, mechanisms related to their transcriptional regulation have not been studied yet. In the present work, transcriptional profiles of both genes were evaluated in trophozoites cultures grown with different iron sources. ehhmbp26 gene was repressed totally by free iron, whereas ehhmbp45 gene showed clearly detectable mRNA levels. Expression profiles for both genes were significantly increased under iron privation condition. Interestingly, ehhmbp26 transcript was highly expressed by Holo-transferrin presence. This induction appears to be independent of direct contact between these proteins, because, in vitro assays evidenced that Ehhmbp26 protein was unable to bind this metalloprotein. Besides, in silico analysis of promoter nucleotide sequences of ehhmbp26 and ehhmbp45 genes revealed some distinctive core promoter elements described in E. histolytica and T-rich regions. Taking altogether these data suggest in E. histolytica dissimilar transcriptional mechanisms involved on iron acquisition control the expression of these genes, and they are unlike to those previously described for instance: in bacteria. Our findings evidenced this pathogen regulates the expression of ehhmbp26 and ehhmbp45 genes depending on the available iron supply, always ensuring the success of its infective process.