Drug resistance in parasites: can we stay ahead of the evolutionary curve?

APDDD: Animal parasitic diseases and drugs database

Animal parasitic diseases not only have an economic impact, but also have serious social and public health impacts. Although antiparasitic drugs can treat these diseases, it seems difficult for users to comprehensively utilize the information, due to incomplete and difficult data collection. Thus, there is an urgent need to establish a comprehensive database, that includes parasitic diseases and related drugs. In this paper, we develop a knowledge database dedicated to collecting and analyzing animal parasitic diseases and related drugs, named Animal Parasitic Diseases and Drugs Database (APDDD). The current version of APDDD includes animal parasitic disease data of 8 major parasite classifications that cause common parasitic diseases and 96 subclass samples mined from many literature and authoritative books, as well as 182 antiparasitic drugs. Furthermore, we utilized APDDD data to add a knowledge graph representing the relationships between parasitic diseases, drugs, and the targeted gene of drugs acting on parasites. We hope that APDDD will become a good database for animal parasitic diseases and antiparasitic drugs research and that users can gain a more intuitive understanding of the relationships between parasitic diseases, drugs, and targeted genes through the knowledge graph.

Anti-parasitic activity of a chimeric peptide Cecropin A (2-8)-Melittin (6-9) (CM11) against tachyzoites of Toxoplasma gondii and the BALB/c mouse model of acute toxoplasmosis

Toxoplasmosis is a zoonotic disease that infects most animals, including humans. Pyrimethamine/sulfadiazine is the standard treatment for toxoplasmosis. Although this treatment has been successful, it is often associated with side effects that cannot be tolerated. Therefore, various compounds have been proposed as alternative treatments for toxoplasmosis. Antimicrobial peptides (AMPs) act on various pathogens, from viruses to protozoa. The purpose of the present study was to evaluate the effects of CM11 on in vitro and in vivo Toxoplasma gondii infection. For in vitro experiments, VERO cells were treated with different concentrations of CM11 (1-128 μg/ml) compared to sulfadiazine (SDZ) (0.78-100 μg/ml). MTT and lactate dehydrogenase (LDH) assays evaluated the cell viability and plasma membrane integrity. Then, the inhibitory concentration (IC50) values were determined for treating tachyzoites of T. gondii before or on cells previously infected. Annexin V-FITC/propidium iodide (PI) staining was used to distinguish viable and apoptotic cells. The effect of CM11, SDZ, and a combination of CM11 and SDZ was evaluated in the BALB/c mouse model of acute toxoplasmosis. CM11 was effective on tachyzoites of T. gondii and had a time and dose-dependent manner. The results of the MTT assay showed that the CC50 values of CM11 and SDZ were estimated at 17.4 µg/ml and 62.3 µg/ml after 24-h, respectively. The inhibitory concentration (IC50) of CM11 and SDZ on infected cells was estimated at 1.9 µg/ml and 1.4 µg/ml after 24-h, respectively. The highest rate of apoptosis (early and late) in high concentrations of SDZ and CM11 was determined for tachyzoites (2.13 % and 13.88 %), non-infected VERO cells (6.1 % and 19.76 %), and infected VERO cells (7.45 % and 29.9 %), respectively. Treating infected mice with CM11 and a combination of CM11 and SDZ had increased survival time. Based on the mentioned results, it can be concluded that CM11 has a beneficial effect on tachyzoites of T. gondii in vitro. The result of the mouse model suggests that CM11, either alone or in combination with other chemotherapeutic agents, could be a potential therapeutic for toxoplasmosis. Hence, antimicrobial peptides could be applied as promising anti-toxoplasma agents for treating toxoplasmosis.

First In Silico Screening of Insect Molecules for Identification of Novel Anti-Parasitic Compounds

Schistosomiasis is a neglected tropical disease caused by blood flukes of the genus Schistosoma. In silico screenings of compounds for the identification of novel anti-parasitic drug candidates have received considerable attention in recent years, including the screening of natural compounds. For the first time, we investigated molecules from insects, a rather neglected source in drug discovery, in an in silico screening approach to find novel antischistosomal compounds. Based on the Dictionary of Natural Products (DNP), we created a library of 1327 insect compounds suitable for molecular docking. A structure-based virtual screening against the crystal structure of a known druggable target in Schistosoma mansoni, the thioredoxin glutathione reductase (SmTGR), was performed. The top ten compounds predominantly originated from beetles and were predicted to interact particularly with amino acids in the doorstop pocket of SmTGR. For one compound from a jewel beetle, buprestin H, we tested and confirmed antischistosomal activity against adult and juvenile parasites in vitro. At concentrations with anti-parasitic activity, we could also exclude any unspecific cytotoxic activity against human HepG2 cells. This study highlights the potential of insect molecules for the identification of novel antischistosomal compounds. Our library of insect-derived molecules could serve not only as basis for future in silico screenings against additional target proteins of schistosomes, but also of other parasites.

Extracellular vesicles as novel assay tools to study cellular interactions of anti-infective compounds - A perspective

Sudden outbreaks of novel infectious diseases and the persistent evolution of antimicrobial resistant pathogens make it necessary to develop specific tools to quickly understand pathogen-cell interactions and to study appropriate drug delivery strategies. Extracellular vesicles (EVs) are cell-specific biogenic transport systems, which are gaining more and more popularity as either diagnostic markers or drug delivery systems. Apart from that, there are emerging possibilities for EVs as tools to study drug penetration, drug-membrane interactions as well as pathogen-membrane interactions. However, it appears that the potential of EVs for such applications has not been fully exploited yet. Considering the vast variety of cells that can be involved in an infection, vesicle-based analytical methods are just emerging and the number of reported applications is still relatively small. Aim of this review is to discuss the current state of the art of EV-based assays, especially in the context of antimicrobial research and therapy, and to present some new perspectives for a more exhaustive and creative exploration in the future.

Where are all the anthelmintics? Challenges and opportunities on the path to new anthelmintics

Control of helminth parasites is a key challenge for human and veterinary medicine. In the absence of effective vaccines and adequate sanitation, prophylaxis and treatment commonly rely upon anthelmintics. There are concerns about the development of drug resistance, side-effects, lack of efficacy and cost-effectiveness that drive the need for new classes of anthelmintics. Despite this need, only three new drug classes have reached the animal market since 2000 and no new classes of anthelmintic have been approved for human use. So where are all the anthelmintics? What are the barriers to anthelmintic discovery, and what emerging opportunities can be used to address this? This was a discussion group focus at the 2019 8th Consortium for Anthelmintic Resistance and Susceptibility (CARS) in Wisconsin, USA. Here we report the findings of the group in the broader context of the human and veterinary anthelmintic discovery pipeline, highlighting challenges unique to antiparasitic drug discovery. We comment on why the development of novel anthelmintics has been so rare. Further, we discuss potential opportunities for drug development moving into the 21st Century.

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

Parasitic infections pose a wide and varying threat globally, impacting over 25% of the global population with many more at risk of infection. These infections are comprised of, but not limited to, toxoplasmosis, malaria, leishmaniasis and any one of a wide variety of helminthic infections. While a great deal is understood about the adaptive immune response to each of these parasites, there remains a need to further elucidate the early innate immune response. Interleukin-33 is being revealed as one of the earliest players in the cytokine milieu responding to parasitic invasion, and as such has been given the name "alarmin." A nuclear cytokine, interleukin-33 is housed primarily within epithelial and fibroblastic tissues and is released upon cellular damage or death. Evidence has shown that interleukin-33 seems to play a crucial role in priming the immune system toward a strong T helper type 2 immune response, necessary in the clearance of some parasites, while disease exacerbating in the context of others. With the possibility of being a double-edged sword, a great deal remains to be seen in how interleukin-33 and its receptor ST2 are involved in the immune response different parasites elicit, and how those parasites may manipulate or evade this host mechanism. In this review article we compile the current cutting-edge research into the interleukin-33 response to toxoplasmosis, malaria, leishmania, and helminthic infection. Furthermore, we provide insight into directions interleukin-33 research may take in the future, potential immunotherapeutic applications of interleukin-33 modulation and how a better clarity of early innate immune system responses involving interleukin-33/ST2 signaling may be applied in development of much needed treatment options against parasitic invaders.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.

Immunomodulatory properties of borage (Echium amoenum) on BALB/c mice infected with Leishmania major

Leishmaniasis is caused by parasitic protozoa transmitted by the bite of a female sand fly and is currently endemic in 88 countries. BALB/c mice are highly susceptible to the infection with the parasite Leishmania major, and this susceptibility has been attributed, in part, to the expansion of Th2 cells, production of their cytokines, and downregulation of Th1 cytokine, interferon gamma (IFN-γ). In this report, we used both aqueous and alcoholic extracts of Iranian borage (Echium amoenum Fisch & C.A. Mey) for treatment of L. major infection in BALB/c mice. We found that both extracts had immunomodulatory properties and increased the level of IFN-γ and lowered the parasite burden in the proximal lymph nodes and prevented the necrosis of the footpad as compared with the untreated infected mice. These results may provide a basis for further studies directed toward the use of the Iranian borage against L. major infection.

Structure determination of glycogen synthase kinase-3 from Leishmania major and comparative inhibitor structure-activity relationships with Trypanosoma brucei GSK-3

Glycogen synthase kinase-3 (GSK-3) is a drug target under intense investigation in pharmaceutical companies and constitutes an attractive piggyback target for eukaryotic pathogens. Two different GSKs are found in trypanosomatids, one about 150 residues shorter than the other. GSK-3 short (GeneDB: Tb927.10.13780) has previously been validated genetically as a drug target in Trypanosoma brucei by RNAi induced growth retardation; and chemically by correlation between enzyme and in vitro growth inhibition. Here, we report investigation of the equivalent GSK-3 short enzymes of L. major (LmjF18.0270) and L. infantum (LinJ18_V3.0270, identical in amino acid sequences to LdonGSK-3 short) and a crystal structure of LmajGSK-3 short at 2 Å resolution. The inhibitor structure-activity relationships (SARs) of L. major and L. infantum are virtually identical, suggesting that inhibitors could be useful for both cutaneous and visceral leishmaniasis. Leishmania spp. GSK-3 short has different inhibitor SARs than TbruGSK-3 short, which can be explained mostly by two variant residues in the ATP-binding pocket. Indeed, mutating these residues in the ATP-binding site of LmajGSK-3 short to the TbruGSK-3 short equivalents results in a mutant LmajGSK-3 short enzyme with SAR more similar to that of TbruGSK-3 short. The differences between human GSK-3β (HsGSK-3β) and LmajGSK-3 short SAR suggest that compounds which selectively inhibit LmajGSK-3 short may be found.

Efficacy of sulfadoxine-pyrimethamine in Tanzania after two years as first-line drug for uncomplicated malaria: assessment protocol and implication for treatment policy strategies

Background

Systematic surveillance for resistant malaria shows high level of resistance of Plasmodium falciparum to sulfadoxine-pyrimethamine (SP) across eastern and southern parts of Africa. This study assessed in vivo SP efficacy after two years of use as an interim first-line drug in Tanzania, and determined the rates of treatment failures obtained after 14 and 28 days of follow-up.

Methods

The study was conducted in the Ipinda, Mlimba and Mkuranga health facilities in Tanzania. Children aged 6–59 months presenting with raised temperature associated exclusively with P. falciparum (1,000–100,000 parasites per μl) were treated with standard dose of SP. Treatment responses were classified according to the World Health Organization (WHO) definition as Adequate Clinical and Parasitological Response (ACPR), Early Treatment Failure (ETF), Late Clinical Failure (LCF) and Late Parasitological Failure (LPF) on day 14 and day 28.

Results

Overall 196 (85.2%) of 230 patients had ACPR on day 14 but only 116 (50.9%) on day 28 (57.7% after excluding new infections by parasite genotyping). Altogether 21 (9.1%) and 13 (5.7%) of the 230 patients assessed up to day 14 and 39 (17.1%) and 55 (24.1%) of the 228 followed up to day 28 had clinical and parasitological failure, respectively.

Conclusion

These findings indicate that SP has low therapeutic value in Tanzania. The recommendation of changing first line treatment to artemether + lumefantrine combination therapy from early next year is, therefore, highly justified. These findings further stress that, for long half-life drugs such as SP, establishment of cut-off points for policy change in high transmission areas should consider both clinical and parasitological responses beyond day 14.

Plant active components - a resource for antiparasitic agents?

Plant essential oils (and/or active components) can be used as alternatives or adjuncts to current antiparasitic therapies. Garlic oil has broad-spectrum activity against Trypanosoma, Plasmodium, Giardia and Leishmania, and Cochlospermum planchonii and Croton cajucara oils specifically inhibit Plasmodium falciparum and Leishmania amazonensis, respectively. Some plant oils have immunomodulatory effects that could modify host-parasite immunobiology, and the lipid solubility of plant oils might offer alternative, transcutaneous delivery routes. The emergence of parasites resistant to current chemotherapies highlights the importance of plant essential oils as novel antiparasitic agents.

Trypanosoma cruzi: Chemotherapeutic effects of clomipramine in mice infected with an isolate obtained from an endemic area

The susceptibility of Trypanosoma cruzi strains to nifurtimox and benznidazole has been investigated and resistant strains have been described. Some tricyclic drugs are lethal for trypomastigote and epimastigote forms of T. cruzi (Tulahuen strain) and prevent the disease in mice. We investigated whether clomipramine, a tricyclic antidepressant drug with anti-trypanothione reductase and anti-calmodulin effects, could be effective in treating Albino Swiss mice infected with trypomastigotes of a new T. cruzi isolate from a chronic patient from an endemic area of Argentina in two different treatment schedules. Both treatment schedules were effective in reducing electrocardiographic changes and preventing myocardial structural damage. The cardiac beta-receptors low affinity was compensated for by an increment in their density. This probably maintained cardiac function since 70% of the mice survived for more than 2 years even though anti-cruzipain titers remained high. These results demonstrate that clomipramine, clinically used as a neuroleptic, could be a promising trypanocidal agent for the treatment of Chagas' disease.