Leishmania amazonensis: Metabolic adaptations induced by resistance to an ABC transporter blocker

Systematic Review of Treatment Failure and Clinical Relapses in Leishmaniasis from a Multifactorial Perspective: Clinical Aspects, Factors Associated with the Parasite and Host

Leishmaniasis is a disease caused by protozoa of the genus Leishmania. Treatment options are limited, and there are frequent cases of treatment failure and clinical relapse. To understand these phenomena better, a systematic review was conducted, considering studies published between 1990 and 2021 in Portuguese, English, and Spanish. The review included 64 articles divided into three categories. Case reports (26 articles) focused on treatment failure and clinical relapse in cutaneous leishmaniasis patients (47.6%), primarily affecting males (74%) and children (67%), regardless of the clinical manifestation. Experimental studies on the parasite (19 articles), particularly with L. major (25%), indicated that alterations in DNA and genic expression (44.82%) played a significant role in treatment failure and clinical relapse. Population data on the human host (19 articles) identified immunological characteristics as the most associated factor (36%) with treatment failure and clinical relapse. Each clinical manifestation of the disease presented specificities in these phenomena, suggesting a multifactorial nature. Additionally, the parasites were found to adapt to the drugs used in treatment. In summary, the systematic review revealed that treatment failure and clinical relapse in leishmaniasis are complex processes influenced by various factors, including host immunology and parasite adaptation.

Cellular Markers for the Identification of Chemoresistant Isolates in Leishmania

Markers to diagnose chemoresistance in infecting Leishmania parasites are urgently required. This is fundamental for patients who do not heal during or after treatment, as they are unresponsive, or patients who relapse at the end of the therapy, suffering from therapeutic failure. Glucose utilization is an indicator of cell viability that closely associates with metabolic activity. In Leishmania, glucose is a source of carbon atoms and is imported into the cell through specific transporters. In experimentally developed chemoresistant Leishmania parasites a significant decrease of the expression of glucose transporters as well as in the cellular accumulation glucose has been described. Alternatively, the electrical membrane potential is an essential parameter for the formation of the electromotive force needed for the acquisition of important nutrients and solutes (e.g., glucose) by cells, and changes in glucose concentration are suggested to constitute a physiological adaptation associated with a chemoresistant phenotype of Leishmania parasites. Here we describe easy methods to measure glucose uptake and the membrane potential in isolates from patient suffering leishmaniasis. Correlation between both parameters might be helpful to identify chemoresistant parasites. Results suggest that the measured kinetics of glucose utilization rate can be correlated with the plasma membrane potential and together used to differentiate between the performance of wild-type and reference parasites on the one hand and parasites isolated from patients with therapeutic failure on the other.

Transcriptional responses of Leishmania (Leishmania) amazonensis in the presence of trivalent sodium stibogluconate

Background

In the last decade, resistance to antimonials has become a serious problem due to the emergence of drug-resistant strains. Therefore, understanding the mechanisms used by Leishmania parasites to survive under drug pressure is essential, particularly for species of medical-veterinary importance such as L. amazonensis.

Methods

Here, we used RNA-seq technology to analyse transcriptome profiles and identify global changes in gene expression between antimony-resistant and -sensitive L. amazonensis promastigotes.

Results

A total of 723 differentially expressed genes were identified between resistant and sensitive lines. Comparative transcriptomic analysis revealed that genes encoding proteins involved in metabolism (fatty acids) and stress response, as well as those associated with antimony resistance in other Leishmania species, were upregulated in the antimony-resistant line. Most importantly, we observed upregulation of genes encoding autophagy proteins, suggesting that in the presence of trivalent stibogluconate (Sb^III) L. amazonensis can activate these genes either as a survival strategy or to induce cell death, as has been observed in other parasites.

Conclusions

This work identified global transcriptomic changes in an in vitro-adapted strain in response to Sb^III. Our results provide relevant information to continue understanding the mechanism used by parasites of the subgenus Leishmania (L. amazonensis) to generate an antimony-resistant phenotype.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3603-8) contains supplementary material, which is available to authorized users.

Growth arrested live-attenuated Leishmania infantum KHARON1 null mutants display cytokinesis defect and protective immunity in mice

There is no safe and efficacious vaccine against human leishmaniasis available and live attenuated vaccines have been used as a prophylactic alternative against the disease. In order to obtain an attenuated Leishmania parasite for vaccine purposes, we generated L. infantum KHARON1 (KH1) null mutants (ΔLikh1). This gene was previously associated with growth defects in L. mexicana. ΔLikh1 was obtained and confirmed by PCR, qPCR and Southern blot. We also generate a KH1 complemented line with the introduction of episomal copies of KH1. Although ΔLikh1 promastigote forms exhibited a growth pattern similar to the wild-type line, they differ in morphology without affecting parasite viability. L. infantum KH1-deficient amastigotes were unable to sustain experimental infection in macrophages, forming multinucleate cells which was confirmed by in vivo attenuation phenotype. The cell cycle analysis of ΔLikh1 amastigotes showed arrested cells at G₂/M phase. ΔLikh1-immunized mice presented reduced parasite burden upon challenging with virulent L. infantum, when compared to naïve mice. An effect associated with increased Li SLA-specific IgG serum levels and IL-17 production. Thus, ΔLikh1 parasites present an infective-attenuated phenotype due to a cytokinesis defect, whereas it induces immunity against visceral leishmaniasis in mouse model, being a candidate for antileishmanial vaccine purposes.

Correlation between glucose uptake and membrane potential in Leishmania parasites isolated from DCL patients with therapeutic failure: a proof of concept

Besides infection with drug-resistant parasites, therapeutic failure in leishmaniasis may be caused by altered drug pharmacokinetics, re-infection, and host immunologic compromise. Our aim has been to evaluate if relapses that occur in patients suffering from diffuse cutaneous leishmaniasis (DCL) associate with changes in the fitness of infecting organisms. Therefore, in isolates from patients suffering DCL, we correlated glucose uptake and plasma membrane potential and compared the results with those obtained from reference strains. The data demonstrate that Leishmania parasites causing DCL incorporate glucose at an efficient rate, albeit without significant changes in the plasma membrane potential as their corresponding reference strains. The isolate that did not change its accumulation rate of glucose compared to its reference strain expressed a less polarized membrane potential that was insensitive to mitochondrial inhibitors, suggesting a metabolic dysfunction that may result in glycolysis being the main source of ATP. The results constitute a proof of concept that indicates that parasites causing DCL adapted well to drug pressure and expressed an increased fitness. That is, that in Leishmania mexicana and Leishmania amazonensis, parasites isolated from DCL patients, a strong modification of the parasite physiology might occur. As consequences, the parasites adapted well to drug pressure, increased their fitness, and they had an efficient glucose uptake rate albeit not significant changes in membrane potential as their corresponding reference strains. Further validation of the concepts herein established and whether or not the third isolate corresponds with a drug-resistant phenotype need to be demonstrated at the genetic level.

Antimony transport mechanisms in resistant leishmania parasites

Antimonial compounds have been used for more than a century in the treatment of the parasitic disease leishmaniasis. Although pentavalent antimonials are still first-line drugs in several developing countries, this class of drugs is no longer recommended in the Indian sub-continent because of the emergence of drug resistance. The precise mechanisms involved in the resistance of leishmania parasites to antimony are still subject to debate. It is now well documented that drug resistance in leishmania parasites is a multifactorial phenomenon involving multiple genes whose expression pattern synergistically leads to the resistance phenotype. The reduction of intracellular antimony accumulation is a frequent change observed in resistant leishmania cells; however, no comprehensive transport model has been presented so far to explain this change and its contribution to Leishmania resistance. The present review firstly covers the actual knowledge on the metabolism of antimonial drugs, the mechanisms of their transmembrane transport and intracellular processing in Leishmania. It further describes both the functional and molecular changes associated with Sb resistance in this organism. Possible transport models based on the actual knowledge are then presented, as well as their functional implications. Biophysical and pharmacological strategies are finally proposed for the precise identification of the transport pathways.

Molecular characterization of the hexose transporter gene in benznidazole resistant and susceptible populations of Trypanosoma cruzi

BACKGROUND

Hexose transporters (HT) are membrane proteins involved in the uptake of energy-supplying glucose and other hexoses into the cell. Previous studies employing the Differential Display technique have shown that the transcription level of the HT gene from T. cruzi (TcrHT) is higher in an in vitro-induced benznidazole (BZ)-resistant population of the parasite (17 LER) than in its susceptible counterpart (17 WTS).

METHODS

In the present study, TcrHT has been characterized in populations and strains of T. cruzi that are resistant or susceptible to BZ. We investigated the copy number and chromosomal location of the gene, the levels of TcrHT mRNA and of TcrHT activity, and the phylogenetic relationship between TcrHT and HTs from other organisms.

RESULTS

In silico analyses revealed that 15 sequences of the TcrHT gene are present in the T. cruzi genome, considering both CL Brener haplotypes. Southern blot analyses confirmed that the gene is present as a multicopy tandem array and indicated a nucleotide sequence polymorphism associated to T. cruzi group I or II. Karyotype analyses revealed that TcrHT is located in two chromosomal bands varying in size from 1.85 to 2.6 Mb depending on the strain of T. cruzi. The sequence of amino acids in the HT from T. cruzi is closely related to the HT sequences of Leishmania species according to phylogenetic analysis. Northern blot and quantitative real-time reverse transcriptase polymerase chain reaction analyses revealed that TcrHT transcripts are 2.6-fold higher in the resistant 17 LER population than in the susceptible 17 WTS. Interestingly, the hexose transporter activity was 40% lower in the 17 LER population than in all other T. cruzi samples analyzed. This phenotype was detected only in the in vitro-induced BZ resistant population, but not in the in vivo-selected or naturally BZ resistant T. cruzi samples. Sequencing analysis revealed that the amino acid sequences of the TcrHT from 17WTS and 17LER populations are identical. This result suggests that the difference in glucose transport between 17WTS and 17LER populations is not due to point mutations, but probably due to lower protein expression level.

CONCLUSION

The BZ resistant population 17 LER presents a decrease in glucose uptake in response to drug pressure.

Gene expression profiling and molecular characterization of antimony resistance in Leishmania amazonensis

Background

Drug resistance is a major problem in leishmaniasis chemotherapy. RNA expression profiling using DNA microarrays is a suitable approach to study simultaneous events leading to a drug-resistance phenotype. Genomic analysis has been performed primarily with Old World Leishmania species and here we investigate molecular alterations in antimony resistance in the New World species L. amazonensis.

Methods/Principal Findings

We selected populations of L. amazonensis promastigotes for resistance to antimony by step-wise drug pressure. Gene expression of highly resistant mutants was studied using DNA microarrays. RNA expression profiling of antimony-resistant L. amazonensis revealed the overexpression of genes involved in drug resistance including the ABC transporter MRPA and several genes related to thiol metabolism. The MRPA overexpression was validated by quantitative real-time RT-PCR and further analysis revealed that this increased expression was correlated to gene amplification as part of extrachromosomal linear amplicons in some mutants and as part of supernumerary chromosomes in other mutants. The expression of several other genes encoding hypothetical proteins but also nucleobase and glucose transporter encoding genes were found to be modulated.

Conclusions/Significance

Mechanisms classically found in Old World antimony resistant Leishmania were also highlighted in New World antimony-resistant L. amazonensis. These studies were useful to the identification of resistance molecular markers.

Leishmania are unicellular microorganisms that can be transmitted to humans by the bite of sandflies. They cause a spectrum of diseases called leishmaniasis, which are classified as neglected tropical diseases by the World Health Organization. The treatment of leishmaniasis is based on the administration of antimony-containing drugs. These drugs have been used since 1947 and still constitute the mainstay for leishmaniasis treatment in several countries. One of the problems with these compounds is the emergence of resistance. Our work seeks to understand how these parasites become resistant to the drug. We studied antimony-resistant Leishmania amazonensis mutants. We analyzed gene expression at the whole genome level in antimony-resistant parasites and identified mechanisms used by Leishmania for resistance. This work could help us in developing new strategies for treatment in endemic countries where people are unresponsive to antimony-based chemotherapy. The identification of common mechanisms among different species of resistant parasites may also contribute to the development of diagnostic kits to identify and monitor the spread of resistance.

Antimony resistance during Visceral Leishmaniasis: A possible consequence of serial mutations in ABC transporters of Leishmania species

Visceral Leishmaniasis is a macrophage associated disorder for the treatment of which antimony based drugs like SAG and SSG were the first choice in the recent past. The clinical value of antimony therapy is now declined against VL because increasing cases of Sodium Antimony Gluconate (SAG) resistance have reached outstanding proportion in Bihar, India. Within this context we looked into the protein sequences of ABC transporters of Leishmania spp associated with Visceral Leishmaniasis that are known to play a crucial role in the development of multidrug resistance (MDR). Our studies consisting of ClustalW, Phylogeny and TCOFFEE have pinpointed that ABC transporters have enormously diverged during the process of evolution even within the identical species strains resulting in insignificant homology and subdued conservation amongst the aminoacid residues. Moreover these amino acid residues remain susceptible to mutations in evolutionary era as indicated by high frequency of variations by the variability studies. Hence we predict that during the process of evolution a series of frequent mutations might have led to changes in the ABC transporters favorable to effluxing the drug thereby making the Leishmania species prone to resistance against the efficient first line drug SAG, used for combating VL. This selection has made them to survive efficiently in the adverse circumstances of antimony based antileishmanial therapy regime.

Availability and applications of ATP-binding cassette (ABC) transporter blockers

ATP-binding cassette (ABC) transporters encompass membrane transport proteins that couple the energy derived from ATP hydrolysis to the translocation of solutes across biological membranes. The functions of these proteins include ancient and conserved mechanisms related to nutrition and pathogenesis in bacteria, spore formation in fungi, and signal transduction, protein secretion and antigen presentation in eukaryotes. Furthermore, one of the major causes of drug resistance and chemotherapeutic failure in both cancer and anti-infective therapies is the active movement of compounds across membranes carried out by ABC transporters. Thus, the clinical relevance of ABC transporters is enormous, and the membrane transporters related to chemoresistance are among the best-studied members of the ABC transporter superfamily. As ABC transporter blockers can be used in combination with current drugs to increase their efficacy, the (possible) impact of efflux pump inhibitors is of great clinical interest. The present review summarizes the progress made in recent years in the identification, design, availability, and applicability of ABC transporter blockers in experimental scenarios oriented towards improving the treatment of infectious diseases caused by microorganisms including parasites.

Leishmania spp.: proficiency of drug-resistant parasites

Leishmaniasis is a disease caused by at least 17 different species of protozoan Leishmania parasites and currently affects around 12 million people living mostly in tropical and subtropical areas. Failure to treat leishmaniasis successfully is often due to drug resistance. However, there are no cellular and molecular markers of chemoresistance against leishmanicidal drugs and the only reliable method for monitoring resistance of individual isolates is the in vitro amastigote/macrophage model. It is thus necessary to find cellular and molecular markers that can be used systematically to identify the drug-resistant phenotype of the infecting parasites. Until now, whether drug resistance in Leishmania compromises parasite proficiency, e.g. in terms of infectivity or metabolism, has not been systematically evaluated. Therefore, here we examine whether the physiological changes expressed by drug-resistant Leishmania reflect a modification of parasite vitality in drug-resistant compared with drug-sensitive parasites. Finally, the clinical implications of drug resistance in Leishmania are also discussed.