Influential Parameters for the Analysis of Intracellular Parasite Metabolomics

Comparison of extraction methods in vitro Plasmodium falciparum: A 1H NMR and LC-MS joined approach

Malaria is a parasitic disease that remains a global concern and the subject of many studies. Metabolomics has emerged as an approach to better comprehend complex pathogens and discover possible drug targets, thus giving new insights that can aid in the development of antimalarial therapies. However, there is no standardized method to extract metabolites from in vitro Plasmodium falciparum intraerythrocytic parasites, the stage that causes malaria. Additionally, most methods are developed with either LC-MS or NMR analysis in mind, and have rarely been evaluated with both tools. In this work, three extraction methods frequently found in the literature were reproduced and samples were analyzed through both LC-MS and 1H NMR, and evaluated in order to reveal which is the most repeatable and consistent through an array of different tools, including chemometrics, peak detection and annotation. The most reliable method in this study proved to be a double extraction with methanol and methanol/water (80:20, v/v). Metabolomic studies in the field should move towards standardization of methodologies and the use of both LC-MS and 1H NMR in order to make data more comparable between studies and facilitate the achievement of biologically interpretable information.

Ring-stage growth arrest: Metabolic basis of artemisinin tolerance in Plasmodium falciparum

The emergence and spread of artemisinin-tolerant malaria parasites threatens malaria control programmes worldwide. Mutations in the propeller domain of the Kelch13 protein confer Plasmodium falciparum artemisinin resistance (ART-R). ART-R is linked to the reduced susceptibility of temporary growth-arrested ring-stage parasites, but the metabolic mechanisms remain elusive. We generated two PfKelch13 mutant lines via CRISPR-Cas9 gene editing which displayed a reduced susceptibility accompanied by an extended ring stage. The metabolome of ART-induced ring-stage growth arrest parasites carrying PfKelch13 mutations showed significant alterations in the tricarboxylic acid (TCA) cycle, glycolysis, and amino acids metabolism, pointing to altered energy and porphyrin metabolism with metabolic plasticity. The critical role of these pathways was further confirmed by altering metabolic flow or through chemical inhibition. Our findings uncover that the growth arrestment associated with ART-R is potentially attributed to the adaptative metabolic plasticity, indicating that the defined metabolic remodeling turns out to be the trigger for ART-R.

Recent metabolomic developments for antimalarial drug discovery

Malaria is a parasitic disease that remains a global health issue, responsible for a significant death and morbidity toll. Various factors have impacted the use and delayed the development of antimalarial therapies, such as the associated financial cost and parasitic resistance. In order to discover new drugs and validate parasitic targets, a powerful omics tool, metabolomics, emerged as a reliable approach. However, as a fairly recent method in malaria, new findings are timely and original practices emerge frequently. This review aims to discuss recent research towards the development of new metabolomic methods in the context of uncovering antiplasmodial mechanisms of action in vitro and to point out innovative metabolic pathways that can revitalize the antimalarial pipeline.

Metabolic flexibility in Trypanosoma cruzi amastigotes: implications for persistence and drug sensitivity

Throughout their life cycle, parasitic organisms experience a variety of environmental conditions. To ensure persistence and transmission, some protozoan parasites are capable of adjusting their replication or converting to distinct life cycle stages. Trypanosoma cruzi is a 'generalist' parasite that is competent to infect various insect (triatomine) vectors and mammalian hosts. Within the mammalian host, T. cruzi replicates intracellularly as amastigotes and can persist for the lifetime of the host. The persistence of the parasites in tissues can lead to the development of Chagas disease. Recent work has identified growth plasticity and metabolic flexibility as aspects of amastigote biology that are important determinants of persistence in varied growth conditions and under drug pressure. A better understanding of the link between amastigote and host/tissue metabolism will aid in the development of new drugs or therapies that can limit disease pathology.

Single-cell sequencing of the small and AT-skewed genome of malaria parasites

Single-cell genomics is a rapidly advancing field; however, most techniques are designed for mammalian cells. We present a single-cell sequencing pipeline for an intracellular parasite, Plasmodium falciparum, with a small genome of extreme base content. Through optimization of a quasi-linear amplification method, we target the parasite genome over contaminants and generate coverage levels allowing detection of minor genetic variants. This work, as well as efforts that build on these findings, will enable detection of parasite heterogeneity contributing to P. falciparum adaptation. Furthermore, this study provides a framework for optimizing single-cell amplification and variant analysis in challenging genomes.

The antimalarial resistome - finding new drug targets and their modes of action

To this day, malaria remains a global burden, affecting millions of people, especially those in sub-Saharan Africa and Asia. The rise of drug resistance to current antimalarial treatments, including artemisinin-based combination therapies, has made discovering new small molecule compounds with novel modes of action an urgent matter. The concerted effort to construct enormous compound libraries and develop high-throughput phenotypic screening assays to find compounds effective at specifically clearing malaria-causing Plasmodium parasites at any stage of the life cycle has provided many antimalarial prospects, but does not indicate their target or mode of action. Here, we review recent advances in antimalarial drug discovery efforts, focusing on the following 'omics' approaches in mode of action studies: IVIEWGA, CETSA, metabolomic profiling.

Data normalization strategies in metabolomics: Current challenges, approaches, and tools

Data normalization is a big challenge in quantitative metabolomics approaches, whether targeted or untargeted. Without proper normalization, the mass-spectrometry and spectroscopy data can provide erroneous, sub-optimal data, which can lead to misleading and confusing biological results and thereby result in failed application to human healthcare, clinical, and other research avenues. To address this issue, a number of statistical approaches and software tools have been proposed in the literature and implemented over the years, thereby providing a multitude of approaches to choose from - either sample-based or data-based normalization strategies. In recent years, new dedicated software tools for metabolomics data normalization have surfaced as well. In this account article, I summarize the existing approaches and the new discoveries and research findings in this area of metabolomics data normalization, and I introduce some recent tools that aid in data normalization.

Cholesterol-dependent enrichment of understudied erythrocytic stages of human Plasmodium parasites

For intracellular pathogens, the host cell provides needed protection and nutrients. A major challenge of intracellular parasite research is collection of high parasite numbers separated from host contamination. This situation is exemplified by the malaria parasite, which spends a substantial part of its life cycle inside erythrocytes as rings, trophozoites, and schizonts, before egress and reinvasion. Erythrocytic Plasmodium parasite forms refractory to enrichment remain understudied due to high host contamination relative to low parasite numbers. Here, we present a method for separating all stages of Plasmodium-infected erythrocytes through lysis and removal of uninfected erythrocytes. The Streptolysin O-Percoll (SLOPE) method is effective on previously inaccessible forms, including circulating rings from malaria-infected patients and artemisinin-induced quiescent parasites. SLOPE can be used on multiple parasite species, under multiple media formulations, and lacks measurable impacts on parasite viability. We demonstrate erythrocyte membrane cholesterol levels modulate the preferential lysis of uninfected host cells by SLO, and therefore modulate the effectiveness of SLOPE. Targeted metabolomics of SLOPE-enriched ring stage samples confirms parasite-derived metabolites are increased and contaminating host material is reduced compared to non-enriched samples. Due to consumption of cholesterol by other intracellular bacteria and protozoa, SLOPE holds potential for improving research on organisms beyond Plasmodium.

Metabolic alterations in the erythrocyte during blood-stage development of the malaria parasite

Background

Human blood cells (erythrocytes) serve as hosts for the malaria parasite Plasmodium falciparum during its 48-h intraerythrocytic developmental cycle (IDC). Established in vitro protocols allow for the study of host–parasite interactions during this phase and, in particular, high-resolution metabolomics can provide a window into host–parasite interactions that support parasite development.

Methods

Uninfected and parasite-infected erythrocyte cultures were maintained at 2% haematocrit for the duration of the IDC, while parasitaemia was maintained at 7% in the infected cultures. The parasite-infected cultures were synchronized to obtain stage-dependent information of parasite development during the IDC. Samples were collected in quadruplicate at six time points from the uninfected and parasite-infected cultures and global metabolomics was used to analyse cell fractions of these cultures.

Results

In uninfected and parasite-infected cultures during the IDC, 501 intracellular metabolites, including 223 lipid metabolites, were successfully quantified. Of these, 19 distinct metabolites were present only in the parasite-infected culture, 10 of which increased to twofold in abundance during the IDC. This work quantified approximately five times the metabolites measured in previous studies of similar research scope, which allowed for more detailed analyses. Enrichment in lipid metabolism pathways exhibited a time-dependent association with different classes of lipids during the IDC. Specifically, enrichment occurred in sphingolipids at the earlier stages, and subsequently in lysophospholipid and phospholipid metabolites at the intermediate and end stages of the IDC, respectively. In addition, there was an accumulation of 18-, 20-, and 22-carbon polyunsaturated fatty acids, which produce eicosanoids and promote gametocytogenesis in infected erythrocyte cultures.

Conclusions

The current study revealed a number of heretofore unidentified metabolic components of the host–parasite system, which the parasite may exploit in a time-dependent manner to grow over the course of its development in the blood stage. Notably, the analyses identified components, such as precursors of immunomodulatory molecules, stage-dependent lipid dynamics, and metabolites, unique to parasite-infected cultures. These conclusions are reinforced by the metabolic alterations that were characterized during the IDC, which were in close agreement with those known from previous studies of blood-stage infection.

Metabolomic Analysis of Toxoplasma gondii Tachyzoites

This protocol describes the use of ¹³C-stable isotope labeling, combined with metabolite profiling, to investigate the metabolism of the tachyzoite stage of the protozoan parasite Toxoplasma gondii. T. gondii tachyzoites can infect any nucleated cell in their vertebrate (including human) hosts, and utilize a range of carbon sources that freely permeate across the limiting membrane of the specialized vacuole within which they proliferate. Methods for cultivating tachyzoites in human foreskin fibroblasts and metabolically labeling intracellular and naturally egressed tachyzoites with a range of ¹³C-labeled carbon sources are described. Parasites are harvested and purified from host metabolites, with rapid metabolic quenching and ¹³C-enrichment in intracellular polar metabolites quantified by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). The mass isotopomer distribution of key metabolites is determined using DExSI software. This method can be used to measure perturbations in parasite metabolism induced by drug inhibition or genetic manipulation of enzyme levels and is broadly applicable to other cultured or intracellular parasite stages.