Babesia microti Aldo-keto Reductase-Like Protein Involved in Antioxidant and Anti-parasite Response

Phylogenetic and transcriptomic study of aldo-keto reductases in Haemonchus contortus and their inducibility by flubendazole

Aldo-keto reductases (AKRs), a superfamily of NADP(H)-dependent oxidoreductases, catalyze the oxidoreduction of a wide variety of eobiotic and xenobiotic aldehydes and ketones. In mammals, AKRs play essential roles in hormone and xenobiotic metabolism, oxidative stress, and drug resistance, but little is known about these enzymes in the parasitic nematode Haemonchus contortus. In the present study, 22 AKR genes existing in the H. contortus genome were investigated and a phylogenetic analysis with comparison to AKRs in Caenorhabditis elegans, sheep and humans was conducted. The constitutive transcription levels of all AKRs were measured in eggs, larvae, and adults of H. contortus, and their expression was compared in a drug-sensitive strain (ISE) and a benzimidazole-resistant strain (IRE) previously derived from the sensitive strain by imposing benzimidazole selection pressure. In addition, the inducibility of AKRs by exposure of H. contortus adults to benzimidazole anthelmintic flubendazole in vitro was tested. Phylogenetic analysis demonstrated that the majority of AKR genes in H. contortus lack orthologues in the sheep genome, which is a favorable finding for considering AKRs as potential drug targets. Large differences in the expression levels of individual AKRs were observed, with AKR1, AKR3, AKR8, and AKR10 being the most highly expressed at most developmental stages. Significant changes in the expression of AKRs during the life cycle and pronounced sex differences were found. Comparing the IRE and ISE strains, three AKRs were upregulated, and seven AKRs were downregulated in adults. In addition, the expression of three AKRs was induced by flubendazole exposure in adults of the ISE strain. Based on these results, AKR1, AKR2, AKR3, AKR5, AKR10 and AKR19 in particular merit further investigation and functional characterization with respect to their potential involvement in drug biotransformation and anthelmintic resistance in H. contortus.

Cancer to Cataracts: The Mechanistic Impact of Aldo-Keto Reductases in Chronic Diseases

Aldo-keto reductases (AKRs) are a superfamily of promiscuous enzymes that have been chiseled by evolution to act as catalysts for numerous regulatory pathways in humans. However, they have not lost their promiscuity in the process, essentially making them a double-edged sword. The superfamily is involved in multiple metabolic pathways and are linked to chronic diseases such as cataracts, diabetes, and various cancers. Unlike other detoxifying enzymes such as cytochrome P450s (CYP450s), short-chain dehydrogenases (SDRs), and medium-chain dehydrogenases (MDRs), that participate in essential pathways, AKRs are more widely distributed and have members with interchangeable functions. Moreover, their promiscuity is ubiquitous across all species and participates in the resistance of pathogenic microbes. Moreover, the introduction of synthetic substrates, such as synthetic molecules and processed foods, results in unwanted "toxification" due to enzyme promiscuity, leading to chronic diseases.

Robenidine Analogues Are Potent Antimalarials in Drug-Resistant Plasmodium falciparum

Robenidine is a veterinary drug used in the poultry industry to treat coccidiosis caused by parasites in the Eimeria genus. Though this compound and related aminoguanidines have recently been studied in other pathogens, the chemotype has not been systematically explored to optimize antimalarial activity despite the close genetic relationship between Eimeria and Plasmodium (both are members of the Apicomplexa phylum of unicellular, spore-forming parasites). In this study, a series of aminoguanidine robenidine analogues was prepared and tested in vitro against Plasmodium falciparum, including multidrug-resistant strains. Selected compounds were further evaluated in vivo against murine Plasmodium yoelii in mice. Iterative structure–activity relationship studies led to the discovery of 1, an aminoguanidine with excellent activity against drug-resistant malaria in vitro and impressive in vivo efficacy with an ED₅₀ value of 0.25 mg/kg/day in a standard 4-day test.

Response of Leucine-Rich Repeat Domain-Containing Protein in Haemaphysalis longicornis to Babesia microti Infection and Its Ligand Identification

Haemaphysalis longicornis is a blood-feeding hard tick known for transmitting a variety of pathogens, including Babesia How the parasites in the imbibed blood become anchored in the midgut of ticks is still unknown. Leucine-rich repeat domain (LRR)-containing protein, which is associated with the innate immune reaction and conserved in many species, has been detected in H. longicornis and has previously been indicated in inhibiting the growth of Babesia gibsoni However, the detailed mechanism is unknown. In this study, one of the ligands for LRR from H. longicornis (HlLRR) was identified in Babesia microti, designated BmActin, using glutathione transferase (GST) pulldown experiments and immunofluorescence assays. Moreover, RNA interference of HlLRR led to a decrease in the BmActin mRNA expression in the midgut of fully engorged ticks which fed on B. microti-infected mice. We also found that the expression level of the innate immune molecules in H. longicornis, defensin, antimicrobial peptides (AMPs), and lysozyme, were downregulated after the knockdown of HlLRR. However, subolesin expression was upregulated. These results indicate that HlLRR not only recognizes BmActin but may also modulate innate immunity in ticks to influence Babesia growth, which will further benefit the development of anti-Babesia vaccines or drugs.

Evaluation of enzymatic activity of Babesia microti thioredoxin reductase (Bmi TrxR)-mutants and screening of its potential inhibitors

Babesia microti is a zoonotic pathogen that mainly parasitizes mammalian erythrocytes. Oxidative stress can induce gene mutation, protein denaturation and lipid peroxidation, such as reactive oxygen species (ROS) induced by hypoxic environment and the host immune system. An antioxidase, B. microti thioredoxin reductase (Bmi TrxR), has been identified in B. microti. We used a combination of homology modeling and domain prediction to explore the functional sites of Bmi TrxR and found that TrxR has three domains. Constructed a mutant pool which His-tag were at the N-terminus (TrxR-Nhis, C105-Nhis, C110-Nhis, C105110-Nhis, C547-Nhis, C552-Nhis, C547552-Nhis) and the His tag were at the N- and C-terminus (TrxR-NChis, C547-NChis, C552-NChis, C547552-NChis). The proteins were expressed as His-tagged fusion proteins in Escherichia coli. The His-tag of TrxR C-terminus were affected the reaction with Trx. The inhibitory efficiency of DNCB was decreased for mutant C547, compared with recombinant TrxR, indicating that the action site of DNCB might be cysteine at position 547. These results indicate that the N-terminal active site of Bmi TrxR plays an important role in accepting electrons and promotes electron transfer. The C-terminus His tag of Bmi TrxR affected the electron transfer and the reducing activity of Bmi TrxR. Reduce reactive oxygen produced in oxidative stress was reduced by Bmi TrxR, which is beneficial to Babesia survival. Therefore, reduction site of TrxR may become a potential target for Babesia microti treatment.

A cysteine protease of Babesia microti and its interaction with tick cystatins

Babesiosis is a tick-borne protozoonosis caused by Babesia, which can cause fever, hemolytic anemia, hemoglobinuria, and even death. Babesia microti is a parasite found in rodents and can be pathogenic to humans. In this study, the full-length cDNA of a B. microti cysteine protease (BmCYP) was expressed and the recombinant rBmCYP protein analyzed and characterized. BmCYP is encoded by an ORF of 1.3 kb, with a predicted molecular weight of 50 kDa and a theoretical pI of 8.5. The amino acid sequence of BmCYP exhibits an identity of 32.9 to 35.2% with cysteine proteases of Babesia ovis, Babesia bovis, and Theileria, respectively. The results of the proteinase assays show that rBmCYP has cysteine protease enzymatic activity. In addition, we demonstrate that tick cystatins rRhcyst-1 and rRhcyst-2 were able to effectively inhibit the activity of rBmCYP; the inhibition rates were 57.2% and 30.9%, respectively. Tick cystatins Rhcyst-1 and Rhcyst-2 were differentially expressed in ticks that fed on Babesia-infected mice relative to non-infected control ticks. Our results suggest that BmCYP is a functional enzyme with cysteine protease enzymatic activity and may be involved in tick-B. microti interactions.

Unraveling oxidative stress response in the cestode parasite Echinococcus granulosus

Cystic hydatid disease (CHD) is a worldwide neglected zoonotic disease caused by Echinococcus granulosus. The parasite is well adapted to its host by producing protective molecules that modulate host immune response. An unexplored issue associated with the parasite's persistence in its host is how the organism can survive the oxidative stress resulting from parasite endogenous metabolism and host defenses. Here, we used hydrogen peroxide (H₂O₂) to induce oxidative stress in E. granulosus protoescoleces (PSCs) to identify molecular pathways and antioxidant responses during H₂O₂ exposure. Using proteomics, we identified 550 unique proteins; including 474 in H₂O₂-exposed PSCs (H-PSCs) samples and 515 in non-exposed PSCs (C-PSCs) samples. Larger amounts of antioxidant proteins, including GSTs and novel carbonyl detoxifying enzymes, such as aldo-keto reductase and carbonyl reductase, were detected after H₂O₂ exposure. Increased concentrations of caspase-3 and cathepsin-D proteases and components of the 26S proteasome were also detected in H-PSCs. Reduction of lamin-B and other caspase-substrate, such as filamin, in H-PSCs suggested that molecular events related to early apoptosis were also induced. We present data that describe proteins expressed in response to oxidative stress in a metazoan parasite, including novel antioxidant enzymes and targets with potential application to treatment and prevention of CHD.

Babesia microti thioredoxin 3 is an effective antioxidant and involved in the response to antiprotozoal drugs

The intra-erythrocytic apicomplexan Babesia microti is the predominant pathogen that causes human babesiosis, an infectious disease that occurs worldwide. B. microti relies on the antioxidant including thioredoxin system to maintain the redox balance during the erythrocytic stage. In the present study, the full-length B. microti thioredoxin 3 (BmTrx3) gene was cloned, expressed in vitro, and its response to antiprotozoal drugs were tested. The full-length BmTrx3 was 663 bp and contained an intact open reading frame of 567 bp. The encoded polypeptide was 188 amino acids and the predicted molecular weight of the protein was 21.7 kDa. A conserved thioredoxin-like family domain was found in BmTrx3. The expression of BmTrx3 was upregulated on both the third and eighth day post-infection in mice, whereas expression was downregulated during the beginning and later stages. Western blot analysis showed that mouse anti-BmTrx3 serum could recognize the native BmTrx3 in parasite lysates and that the mouse anti-B. microti serum could recognize the recombinant BmTrx3 protein. Immunofluorescence microscopy showed that BmTrx3 localized in the cell cytoplasm of B. microti merozoites in B. microti-infected red blood cells. The results of bovine insulin reduction assay indicated the enzyme activity of the purified recombinant BmTrx3 protein. The anti-malaria drug chloroquine significantly inhibited the expression of BmTrx3, however, another anti-malaria drug qunine, and a known anti-babesiosis drug clindamycin, induced significantly higher upregulation of BmTrx3 mRNA. The results of the present study demonstrate that BmTrx3 is a functional enzyme with antioxidant activity and may be involved in the response of B. microti to anti-parasite drugs.

Molecular characterization of Babesia microti thioredoxin (BmTrx2) and its expression patterns induced by antiprotozoal drugs

Background

Human babesiosis is an infectious disease that is epidemic in various regions all over the world. The predominant causative pathogen of this disease is the intra-erythrocytic parasite Babesia microti. The thioredoxin system is one of the major weapons that is used in the resistance to the reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced by host immune system. In other intra-erythrocytic apicomplexans like the malaria parasite Plasmodium falciparum, anti-oxidative proteins are promising targets for the development of anti-parasitic drugs. However, to date, the sequences and biological properties of thioredoxins and thioredoxin-like molecules of B. microti remain unknown. Understanding the molecular characterization and function of B. microti thioredoxins may help to develop anti-Babesia drugs and controlling babesiosis.

Methods

The full-length B. microti thioredoxin 2 (BmTrx2) gene was obtained using a rapid amplification of cDNA ends (RACE) method, and the deduced BmTrx2 amino acid sequence was analyzed using regular bioinformatics tools. Recombinant BmTrx2 protein was expressed in vitro and purified using His-tag protein affinity chromatography resins. Reverse transcription PCR, quantitative real-time PCR and Western blot were employed to detect the expression and native proteins of BmTrx2. Indirect immunofluorescence assay was used to localize BmTrx2 in B. microti. Bovine insulin reduction assays were used to determine the enzyme activity of the purified recombinant BmTrx2 protein.

Results

The full-length BmTrx2 was 564 bp with a 408 bp open reading frame encoding a protein of 135 amino acids. The predicted molecular weight of the protein was 15.5 kDa. A conserved thioredoxin-like family domain was found in BmTrx2. The expression of BmTrx2 was upregulated on both the third and eighth day post-infection in mice, whereas expression was downregulated during the beginning and later stages. The results of Western blot analysis showed the native BmTrx2 in parasite lysates could be detected by mouse anti-BmTrx2 serum and that the recombinant BmTrx2 protein could be recognized by serum of B. microti-infected mice. Immunofluorescence microscopy showed that BmTrx2 localized in the cell cytoplasm of B. microti merozoites in B. microti-infected red blood cells. The results of bovine insulin reduction assay indicated the purified recombinant BmTrx2 protein possesses antioxidant enzyme activity. Dihydroartemisinin and quinine, known anti-malaria drugs, and clindamycin, a known anti-babesiosis drug, induced significantly higher upregulation of BmTrx2 mRNA.

Conclusions

Our results indicate that BmTrx2 is a functional enzyme with antioxidant activity and may be involved in the response of B. microti to anti-parasite drugs.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2619-9) contains supplementary material, which is available to authorized users.