Amino acid derangements in adults with severe falciparum malaria

Amino acid supplementation confers protection to red blood cells before Plasmodium falciparum bystander stress

ABSTRACT

Malaria is a highly oxidative parasitic disease in which anemia is the most common clinical symptom. A major contributor to the malarial anemia pathogenesis is the destruction of bystander, uninfected red blood cells (RBCs). Metabolic fluctuations are known to occur in the plasma of individuals with acute malaria, emphasizing the role of metabolic changes in disease progression and severity. Here, we report conditioned medium from Plasmodium falciparum culture induces oxidative stress in uninfected, catalase-depleted RBCs. As cell-permeable precursors to glutathione, we demonstrate the benefit of pre-exposure to exogenous glutamine, cysteine, and glycine amino acids for RBCs. Importantly, this pretreatment intrinsically prepares RBCs to mitigate oxidative stress.

Longitudinal associations of plasma amino acid levels with recovery from malarial coma

Background

Disordered amino acid metabolism is observed in cerebral malaria (CM). We sought to determine whether abnormal amino acid concentrations were associated with level of consciousness in children recovering from coma. We quantified 21 amino acids and coma scores longitudinally and analyzed data for associations.

Methods

In a prospective observational study, we enrolled 42 children with CM. We measured amino acid levels at entry and at frequent intervals thereafter and assessed consciousness by Blantyre Coma Scores (BCS). Thirty-six healthy children served as controls for in-country normal amino acid ranges. We employed logistic regression using a generalized linear mixed-effects model to assess associations between out-of-range amino acid levels and BCS.

Results

At entry 16/21 amino acid levels were out-of-range. Longitudinal analysis revealed 10/21 out-of-range amino acids were significantly associated with BCS. Elevated phenylalanine levels showed the highest association with low BCS. This finding held when out-of-normal-range data were analyzed at each sampling time.

Discussion

We provide longitudinal data for associations between abnormal amino acid levels and recovery from CM. Of 10 amino acids significantly associated with BCS, we propose that elevated phenylalanine may be a surrogate for impaired clearance of ether lipid mediators of inflammation contributing to CM pathogenesis.

The intersection of host in vivo metabolism and immune responses to infection with kinetoplastid and apicomplexan parasites

SUMMARYProtozoan parasite infection dramatically alters host metabolism, driven by immunological demand and parasite manipulation strategies. Immunometabolic checkpoints are often exploited by kinetoplastid and protozoan parasites to establish chronic infection, which can significantly impair host metabolic homeostasis. The recent growth of tools to analyze metabolism is expanding our understanding of these questions. Here, we review and contrast host metabolic alterations that occur in vivo during infection with Leishmania, trypanosomes, Toxoplasma, Plasmodium, and Cryptosporidium. Although genetically divergent, there are commonalities among these pathogens in terms of metabolic needs, induction of the type I immune responses required for clearance, and the potential for sustained host metabolic dysbiosis. Comparing these pathogens provides an opportunity to explore how transmission strategy, nutritional demand, and host cell and tissue tropism drive similarities and unique aspects in host response and infection outcome and to design new strategies to treat disease.

Starvation induces changes in abundance and small RNA cargo of extracellular vesicles released from Plasmodium falciparum infected red blood cells

The lethal malaria parasite Plasmodium falciparum needs to constantly respond and adapt to changes within the human host in order to survive and transmit. One such change is composed of nutritional limitation, which is augmented with increased parasite loads and intimately linked to severe disease development. Extracellular vesicles released from infected red blood cells have been proposed as important mediators of disease pathogenesis and intercellular communication but whether important for the parasite response to nutritional availability is unknown. Therefore, we investigated the abundance and small RNA cargo of extracellular vesicles released upon short-term nutritional starvation of P. falciparum in vitro cultures. We show that primarily ring-stage parasite cultures respond to glucose and amino acid deprivation with an increased release of extracellular vesicles. Small RNA sequencing of these extracellular vesicles further revealed human miRNAs and parasitic tRNA fragments as the main constituent biotypes. Short-term starvations led to alterations in the transcriptomic profile, most notably in terms of the over-represented biotypes. These data suggest a potential role for extracellular vesicles released from P. falciparum infected red blood cells in the response to nutritional perturbations, their potential as prognostic biomarkers and point towards an evolutionary conserved role among protozoan parasites.

Amino acid supplementation confers protection to red blood cells prior to Plasmodium falciparum bystander stress

Malaria is a highly oxidative parasitic disease in which anemia is the most common clinical symptom. A major contributor to malarial anemia pathogenesis is the destruction of bystander, uninfected red blood cells. Metabolic fluctuations are known to occur in the plasma of individuals with acute malaria, emphasizing the role of metabolic changes in disease progression and severity. Here, we report that conditioned media from Plasmodium falciparum culture induces oxidative stress in healthy uninfected RBCs. Additionally, we show the benefit of amino acid pre-exposure for RBCs and how this pre-treatment intrinsically prepares RBCs to mitigate oxidative stress.

Key points

Intracellular ROS is acquired in red blood cells incubated with Plasmodium falciparum conditioned media Glutamine, cysteine, and glycine amino acid supplementation increased glutathione biosynthesis and reduced ROS levels in stressed RBCs.

Cerebrospinal fluid biomarkers provide evidence for kidney-brain axis involvement in cerebral malaria pathogenesis

Introduction

Cerebral malaria is one of the most severe manifestations of malaria and is a leading cause of acquired neurodisability in African children. Recent studies suggest acute kidney injury (AKI) is a risk factor for brain injury in cerebral malaria. The present study evaluates potential mechanisms of brain injury in cerebral malaria by evaluating changes in cerebrospinal fluid measures of brain injury with respect to severe malaria complications. Specifically, we attempt to delineate mechanisms of injury focusing on blood-brain-barrier integrity and acute metabolic changes that may underlie kidney-brain crosstalk in severe malaria.

Methods

We evaluated 30 cerebrospinal fluid (CSF) markers of inflammation, oxidative stress, and brain injury in 168 Ugandan children aged 18 months to 12 years hospitalized with cerebral malaria. Eligible children were infected with Plasmodium falciparum and had unexplained coma. Acute kidney injury (AKI) on admission was defined using the Kidney Disease: Improving Global Outcomes criteria. We further evaluated blood-brain-barrier integrity and malaria retinopathy, and electrolyte and metabolic complications in serum.

Results

The mean age of children was 3.8 years (SD, 1.9) and 40.5% were female. The prevalence of AKI was 46.3% and multi-organ dysfunction was common with 76.2% of children having at least one organ system affected in addition to coma. AKI and elevated blood urea nitrogen, but not other measures of disease severity (severe coma, seizures, jaundice, acidosis), were associated with increases in CSF markers of impaired blood-brain-barrier function, neuronal injury (neuron-specific enolase, tau), excitatory neurotransmission (kynurenine), as well as altered nitric oxide bioavailability and oxidative stress (p < 0.05 after adjustment for multiple testing). Further evaluation of potential mechanisms suggested that AKI may mediate or be associated with CSF changes through blood-brain-barrier disruption (p = 0.0014), ischemic injury seen by indirect ophthalmoscopy (p < 0.05), altered osmolality (p = 0.0006) and through alterations in the amino acids transported into the brain.

Conclusion

In children with cerebral malaria, there is evidence of kidney-brain injury with multiple potential pathways identified. These changes were specific to the kidney and not observed in the context of other clinical complications.

Diagnosis of cerebral malaria: Tools to reduce Plasmodium falciparum associated mortality

Cerebral malaria (CM) is a major cause of mortality in Plasmodium falciparum (Pf) infection and is associated with the sequestration of parasitised erythrocytes in the microvasculature of the host's vital organs. Prompt diagnosis and treatment are key to a positive outcome in CM. However, current diagnostic tools remain inadequate to assess the degree of brain dysfunction associated with CM before the window for effective treatment closes. Several host and parasite factor-based biomarkers have been suggested as rapid diagnostic tools with potential for early CM diagnosis, however, no specific biomarker signature has been validated. Here, we provide an updated review on promising CM biomarker candidates and evaluate their applicability as point-of-care tools in malaria-endemic areas.

Malaria disrupts the rhesus macaque gut microbiome

Previous studies have suggested that a relationship exists between severity and transmissibility of malaria and variations in the gut microbiome, yet only limited information exists on the temporal dynamics of the gut microbial community during a malarial infection. Here, using a rhesus macaque model of relapsing malaria, we investigate how malaria affects the gut microbiome. In this study, we performed 16S sequencing on DNA isolated from rectal swabs of rhesus macaques over the course of an experimental malarial infection with Plasmodium cynomolgi and analyzed gut bacterial taxa abundance across primary and relapsing infections. We also performed metabolomics on blood plasma from the animals at the same timepoints and investigated changes in metabolic pathways over time. Members of Proteobacteria (family Helicobacteraceae) increased dramatically in relative abundance in the animal's gut microbiome during peak infection while Firmicutes (family Lactobacillaceae and Ruminococcaceae), Bacteroidetes (family Prevotellaceae) and Spirochaetes amongst others decreased compared to baseline levels. Alpha diversity metrics indicated decreased microbiome diversity at the peak of parasitemia, followed by restoration of diversity post-treatment. Comparison with healthy subjects suggested that the rectal microbiome during acute malaria is enriched with commensal bacteria typically found in the healthy animal's mucosa. Significant changes in the tryptophan-kynurenine immunomodulatory pathway were detected at peak infection with P. cynomolgi, a finding that has been described previously in the context of P. vivax infections in humans. During relapses, which have been shown to be associated with less inflammation and clinical severity, we observed minimal disruption to the gut microbiome, despite parasites being present. Altogether, these data suggest that the metabolic shift occurring during acute infection is associated with a concomitant shift in the gut microbiome, which is reversed post-treatment.

Plasma Amino Acid Concentrations in Children With Severe Malaria Are Associated With Mortality and Worse Long-term Kidney and Cognitive Outcomes

BACKGROUND

Global changes in amino acid levels have been described in severe malaria (SM), but the relationship between amino acids and long-term outcomes in SM has not been evaluated.

METHODS

We measured enrollment plasma concentrations of 20 amino acids using high-performance liquid chromatography in 500 Ugandan children aged 18 months to 12 years, including 122 community children and 378 children with SM. The Kidney Disease: Improving Global Outcomes criteria were used to define acute kidney injury (AKI) at enrollment and chronic kidney disease (CKD) at 1-year follow-up. Cognition was assessed over 2 years of follow-up.

RESULTS

Compared to laboratory-defined, age-specific reference ranges, there were deficiencies in sulfur-containing amino acids (methionine, cysteine) in both community children and children with SM. Among children with SM, global changes in amino acid concentrations were observed in the context of metabolic complications including acidosis and AKI. Increases in threonine, leucine, and valine were associated with in-hospital mortality, while increases in methionine, tyrosine, lysine, and phenylalanine were associated with postdischarge mortality and CKD. Increases in glycine and asparagine were associated with worse attention in children <5 years of age.

CONCLUSIONS

Among children with SM, unique amino acid profiles are associated with mortality, CKD, and worse attention.

Comparative Analysis of Host Metabolic Alterations in Murine Malaria Models with Uncomplicated or Severe Malaria

Malaria varies in severity, with complications ranging from uncomplicated to severe malaria. Severe malaria could be attributed to peripheral hyperparasitemia or cerebral malaria. The metabolic interactions between the host and Plasmodium species are yet to be understood during these infections of varied pathology and severity. An untargeted metabolomics approach utilizing the liquid chromatography-mass spectrometry platform has been used to identify the affected host metabolic pathways and associated metabolites in the serum of murine malaria models with uncomplicated malaria, hyperparasitemia, and experimental cerebral malaria. We report that mice with malaria share similar metabolic attributes like higher levels of bile acids, bile pigments, and steroid hormones that have been reported for human malaria infections. Moreover, in severe malaria, upregulated levels of metabolites like phenylalanine, histidine, valine, pipecolate, ornithine, and pantothenate, with decreased levels of arginine and hippurate, were observed. Metabolites of sphingolipid metabolism were upregulated in experimental cerebral malaria. Higher levels of 20-hydroxy-leukotriene B₄ and epoxyoctadecamonoenoic acids were found in uncomplicated malaria, with lower levels observed for experimental cerebral malaria. Our study provides insights into host biology during different pathological stages of malaria disease and would be useful for the selection of animal models for evaluating diagnostic and therapeutic interventions against malaria. The raw data files are available via MetaboLights with the identifier MTBLS4387.

Amino acid signature during sickle cell pain crisis shows significant alterations related to nitric oxide and energy metabolism

Nitric oxide depletion secondary to arginase induced arginine deficiency has been shown to be important in the pathophysiology of vaso-occlusion in sickle cell pain crisis. Our objective of this study was to perform a comprehensive amino acid evaluation during sickle cell pain crisis. In a total of 58 subjects (29 in steady-state sickle cell disease and 29 with sickle cell pain crisis), the amino acids related to nitric oxide pathway was significantly decreased during sickle cell pain crisis compared to steady-state sickle cell disease: arginine (p = 0.001), citrulline (p = 0.012), and ornithine (p = 0.03). In addition, the amino acids related to energy metabolism was significantly decreased during a pain crisis: asparagine (p < 0.001), serine (p = 0.002), histidine (p = 0.017), alanine (p = 0.004), tyrosine (p = 0.012), methionine (p = 0.007), cystine (p = 0.016), isoleucine (p = 0.016) and lysine (p = 0.006). The amino acid related to oxidative stress were significantly higher during a sickle cell pain crisis (glutamic acid (p < 0.001). Furthermore, multivariate analysis with partial least squares-discriminant analysis (PLS-DA) showed that deficiencies of the amino acids arginine, asparagine, citrulline, methionine and alanine were the most important related to sickle cell pain crisis.

The Metabolomic Profiles of Sera of Mice Infected with Plasmodium berghei and Treated by Effective Fraction of Naja naja oxiana Using 1H Nuclear Magnetic Resonance Spectroscopy

BACKGROUND

The use of venom fractions from the Iranian cobra could be useful adjunct treatments of malaria with chloroquine. A metabolomic investigation with ¹HNMR spectroscopy was conducted on an effective fraction tested earlier using Plasmodium berghei as an experimental murine model.

PURPOSE

We sought to ascertain both safety and anti-parasitic effects of experimental therapies.

METHODS

After purification of the venom fractions, 25 mice were infected, then treated for 4 days with 0.2 ml of 5 mg/kg, 2.5 mg/kg and 1 mg/kg of the effective fraction, chloroquine, and a drug vehicle. An ED50 was obtained using Giemsa staining and real-time PCR analysis. The toxicity tests inspecting both liver and kidney tissues were performed.

RESULTS

A clear inhibitory effect on parasitaemia was observed (with 75% inhibition with 5 mg/kg and 50% reduction when 2.5 mg/kg dosage used). ED50 obtained 2.5 mg/kg. The metabolomics were identified as differentiation of aminoacyl-t-RNA biosynthesis, valine, leucine, isoleucine biosynthesis and degradation pathways were observed.

CONCLUSION

Upon therapeutic effects of cobra venom fraction, further optimization of dose-dependent response of pharmacokinetics would be worthwhile for further exploration in adjunct experimental venom therapies.

An in vitro study on the differentiated metabolic mechanism of chloroquine-resistant Plasmodium falciparum using high-resolution metabolomics

Chloroquine (CQ) is an important drug used therapeutically for treatment of malaria. However, due to limited number of studies on metabolic targets of chloroquine (CQ), it is difficult to attribute mechanisms underlying resistance associated with usage of this drug. The present study aimed to investigate the metabolic signatures of CQ-resistant Plasmodium falciparum (PfDd2) compared to CQ-sensitive Plasmodium falciparum (Pf3D7). Both Pf3D7 and PfDd2 were treated with CQ at 200 nM for 48 hr; thereafter, the harvested red blood cells (RBCs) and media were subjected to microscopy and high-resolution metabolomics (HRM). Glutathione, γ-L-glutamyl-L-cysteine, spermidine, inosine monophosphate, alanine, and fructose-1,6-bisphosphate were markedly altered in PfDd2 of RBC. In the media, cysteine, cysteic acid, spermidine, phenylacetaldehyde, and phenylacetic acid were significantly altered in PfDd2. These differential metabolic signatures related signaling pathways of PfDd2, such as oxidative stress pathway and glycolysis may provide evidence for understanding the resistance mechanism and pathogenesis of the CQ-resistant parasite.

Metabolomic Analysis of Diverse Mice Reveals Hepatic Arginase-1 as Source of Plasma Arginase in Plasmodium chabaudi Infection

Infections disrupt host metabolism, but the factors that dictate the nature and magnitude of metabolic change are incompletely characterized. To determine how host metabolism changes in relation to disease severity in murine malaria, we performed plasma metabolomics on eight Plasmodium chabaudi-infected mouse strains with diverse disease phenotypes. We identified plasma metabolic biomarkers for both the nature and severity of different malarial pathologies. A subset of metabolic changes, including plasma arginine depletion, match the plasma metabolomes of human malaria patients, suggesting new connections between pathology and metabolism in human malaria. In our malarial mice, liver damage, which releases hepatic arginase-1 (Arg1) into circulation, correlated with plasma arginine depletion. We confirmed that hepatic Arg1 was the primary source of increased plasma arginase activity in our model, which motivates further investigation of liver damage in human malaria patients. More broadly, our approach shows how leveraging phenotypic diversity can identify and validate relationships between metabolism and the pathophysiology of infectious disease. IMPORTANCE Malaria is a severe and sometimes fatal infectious disease endemic to tropical and subtropical regions. Effective vaccines against malaria-causing Plasmodium parasites remain elusive, and malaria treatments often fail to prevent severe disease. Small molecules that target host metabolism have recently emerged as candidates for therapeutics in malaria and other diseases. However, our limited understanding of how metabolites affect pathophysiology limits our ability to develop new metabolite therapies. By providing a rich data set of metabolite-pathology correlations and by validating one of those correlations, our work is an important step toward harnessing metabolism to mitigate disease. Specifically, we showed that liver damage in P. chabaudi-infected mice releases hepatic arginase-1 into circulation, where it may deplete plasma arginine, a candidate malaria therapeutic that mitigates vascular stress. Our data suggest that liver damage may confound efforts to increase levels of arginine in human malaria patients.

Nonlethal Plasmodium yoelii Infection Drives Complex Patterns of Th2-Type Host Immunity and Mast Cell-Dependent Bacteremia

Malaria strongly predisposes to bacteremia, which is associated with sequestration of parasitized red blood cells and increased gastrointestinal permeability. The mechanisms underlying this disruption are poorly understood. Here, we evaluated the expression of factors associated with mast cell activation and malaria-associated bacteremia in a rodent model. C57BL/6J mice were infected with Plasmodium yoeliiyoelli 17XNL, and blood and tissues were collected over time to assay for circulating levels of bacterial 16S DNA, IgE, mast cell protease 1 (Mcpt-1) and Mcpt-4, Th1 and Th2 cytokines, and patterns of ileal mastocytosis and intestinal permeability.

Malaria strongly predisposes to bacteremia, which is associated with sequestration of parasitized red blood cells and increased gastrointestinal permeability. The mechanisms underlying this disruption are poorly understood. Here, we evaluated the expression of factors associated with mast cell activation and malaria-associated bacteremia in a rodent model. C57BL/6J mice were infected with Plasmodium yoeliiyoelli 17XNL, and blood and tissues were collected over time to assay for circulating levels of bacterial 16S DNA, IgE, mast cell protease 1 (Mcpt-1) and Mcpt-4, Th1 and Th2 cytokines, and patterns of ileal mastocytosis and intestinal permeability. The anti-inflammatory cytokines (interleukin-4 [IL-4], IL-6, and IL-10) and MCP-1/CCL2 were detected early after P. yoeliiyoelii 17XNL infection. This was followed by the appearance of IL-9 and IL-13, cytokines known for their roles in mast cell activation and growth-enhancing activity as well as IgE production. Later increases in circulating IgE, which can induce mast cell degranulation, as well as Mcpt-1 and Mcpt-4, were observed concurrently with bacteremia and increased intestinal permeability. These results suggest that P. yoeliiyoelii 17XNL infection induces the production of early cytokines that activate mast cells and drive IgE production, followed by elevated IgE, IL-9, and IL-13 that maintain and enhance mast cell activation while disrupting the protease/antiprotease balance in the intestine, contributing to epithelial damage and increased permeability.