Recent developments and future prospects in the treatment of visceral leishmaniasis

Prediction of an immunogenic peptide ensemble and multi-subunit vaccine for Visceral leishmaniasis using bioinformatics approaches

Visceral Leishmaniasis (VL) is a neglected tropical disease of public health importance in the Indian subcontinent. Despite consistent elimination initiatives, the disease has not yet been eliminated and there is an increased risk of resurgence from active VL reservoirs including asymptomatic, post kala azar dermatitis leishmaniasis (PKDL) and HIV-VL co-infected individuals. To achieve complete elimination and sustain it in the long term, a prophylactic vaccine, which can elicit long lasting immunity, is desirable. In this study, we employed immunoinformatic tools to design a multi-subunit epitope vaccine for the Indian population by targeting antigenic secretory proteins screened from the Leishmania donovani proteome. Out of 8014 proteins, 277 secretory proteins were screened for their cellular location and proteomic evidence. Through NCBI BlastP, unique fragments of the proteins were cropped, and their antigenicity was evaluated. B-cell, HTL and CTL epitopes as well as IFN-ɣ, IL-17, and IL-10 inducers were predicted, manually mapped to the fragments and common regions were tabulated forming a peptide ensemble. The ensemble was evaluated for Class I MHC immunogenicity and toxicity. Further, immunogenic peptides were randomly selected and used to design vaccine constructs. Eight vaccine constructs were generated by linking random peptides with GS linkers. Synthetic TLR-4 agonist, RS09 was used as an adjuvant and linked with the constructs using EAAK linkers. The predicted population coverage of the constructs was ∼99.8 % in the Indian as well as South Asian populations. The most antigenic, nontoxic, non-allergic construct was chosen for the prediction of secondary and tertiary structures. The 3D structures were refined and analyzed using Ramachandran plot and Z-scores. The construct was docked with TLR-4 receptor. Molecular dynamic simulation was performed to check for the stability of the docked complex. Comparative in silico immune simulation studies showed that the predicted construct elicited humoral and cell-mediated immunity in human host comparable to that elicited by Leish-F3, which is a promising vaccine candidate for human VL.

The role of natural anti-parasitic guided development of synthetic drugs for leishmaniasis

Leishmaniasis is a parasitic disease and categorised as a neglected tropical disease (NTD). Each year, between 70,0000 and 1 million new cases are believed to occur. There are approximately 90 sandfly species which can spread the Leishmania parasites (over 20 species) causing 20,000 to 30,000 death per year. Currently, leishmaniasis has no specific therapeutic treatment available. The prescribed drugs with several drawbacks including high cost, challenging administration, toxicity, and drug resistance led to search for the alternative treatment with less toxicity and selectivity. Introducing the molecular features like that of phytoconstituents for the search of compounds with less toxicity is another promising approach. The current review classifies the synthetic compounds according to the core rings present in the natural phytochemicals for the development of antileishmanial agents (2020-2022). Considering the toxicity and limitations of synthetic analogues, natural compounds are at the higher notch in terms of effectiveness and safety. Synthesized compounds of chalcones (Compound 8; IC₅₀: 0.03 μM, 4.7 folds more potent than Amphotericin B; IC₅₀: 0.14 μM), pyrimidine (compound 56; against L. tropica; 0.04 μM and L. infantum; 0.042 μM as compared to glucantime: L. tropica; 8.17 μM and L. infantum; 8.42 μM), quinazoline and (compound 72; 0.021 μM, 150 times more potent than miltefosine). The targeted delivery against DHFR have been demonstrated by one of the pyrimidine compounds 62 with an IC₅₀ value of 0.10 μM against L. major as compared to the standard trimethoprim (IC₅₀: 20 μM). The review covers the medicinal importance of antileishmanial agents from synthetic and natural sources such as chalcone, pyrazole, coumarins, steroids, and alkaloidal-containing drugs (indole, quinolines, pyridine, pyrimidine, carbolines, pyrrole, aurones, and quinazolines). The efforts of introducing the core rings present in the natural phytoconstituents as antileishmanial in the synthetic compounds are discussed with their structural activity relationship. The perspective will support the medicinal chemists in refining and directing the development of novel molecules phytochemicals-based antileishmanial agents.

Emerging leishmaniasis in southern Himalayas: A mini-review

Leishmaniasis is a vector-borne parasitic disease affecting millions of people worldwide. However, in the last decade, the number of cases has been reduced from well-documented endemic parts, but sporadic cases have been reported widely from various non-endemic areas, especially from the southern Himalayan zone. This raises concerns about the emergence of new ecological niches. This warrants a critical evaluation of key factors causing this rapid spread and possibly indigenous transmission. This mini-review article is aimed to briefly address the parasite, the vector, and the environmental aspects in the transmission of leishmaniasis in these new foci against a background of worldwide endemic leishmaniasis with a special focus on the southern Himalayan zone. As the lack of knowledge about the causative parasites, vectors, reservoir hosts, atypical presentations, and their management make the problem serious and may lead to the emergence of public health issues. The present works also reviewed the existing information regarding clinical variations, diagnostic methods, treatment, its outcome, and ignite for further research in these aspects of the disease.

Immunoproteomics approach for the discovery of antigens applied to the diagnosis of canine visceral leishmaniasis

In the present study, an immunoproteomic approach using Leishmania infantum parasites isolated from naturally infected dogs from an endemic region of the disease, was carried out to identify new antigens to be used in the diagnosis of canine visceral leishmaniasis (CVL). Protein extracts, obtained from parasites isolated from asymptomatic (CanLA) and symptomatic (CanLS) dogs, were used to perform the two-dimensional gels. Western Blotting assays were carried out by employing a pool of sera from dogs with visceral leishmaniasis (CanLA or CanLS), healthy dogs from an endemic area, or dogs with similar diseases associated with cross-reactions (babesiosis and ehrlichiosis). With these results, it was possible to exclude the spots that showed a cross-reactivity of the sera from groups of healthy dogs, and those with babesiosis or ehrlichiosis. Taken together, 20 proteins were identified, 15 of which have already been described in the literature and 5 of which are hypothetical. An immunogenomic screen strategy was applied to identify conserved linear B-cell epitopes in the identified hypothetical proteins. Two peptides were synthesized and tested in ELISA experiments as a proof of concept for the validation of our immunoproteomics findings. The results demonstrated that the antigens presented sensitivity and specificity values ranging from 81.93% to 97.59% and 78.14 to 85.12%, respectively. As a comparative antigen, a preparation of a Leishmania extract showed sensitivity and specificity values of 75.90% and 74.88%, respectively. The present study was able to identify proteins capable of being used for the serodiagnosis of canine visceral leishmaniasis.

Parasite Metalo-aminopeptidases as Targets in Human Infectious Diseases

BACKGROUND

Parasitic human infectious diseases are a worldwide health problem due to the increased resistance to conventional drugs. For this reason, the identification of novel molecular targets and the discovery of new chemotherapeutic agents are urgently required. Metalo- aminopeptidases are promising targets in parasitic infections. They participate in crucial processes for parasite growth and pathogenesis.

OBJECTIVE

In this review, we describe the structural, functional and kinetic properties, and inhibitors, of several parasite metalo-aminopeptidases, for their use as targets in parasitic diseases.

CONCLUSION

Plasmodium falciparum M1 and M17 aminopeptidases are essential enzymes for parasite development, and M18 aminopeptidase could be involved in hemoglobin digestion and erythrocyte invasion and egression. Trypanosoma cruzi, T. brucei and Leishmania major acidic M17 aminopeptidases can play a nutritional role. T. brucei basic M17 aminopeptidase down-regulation delays the cytokinesis. The inhibition of Leishmania basic M17 aminopeptidase could affect parasite viability. L. donovani methionyl aminopeptidase inhibition prevents apoptosis but not the parasite death. Decrease in Acanthamoeba castellanii M17 aminopeptidase activity produces cell wall structural modifications and encystation inhibition. Inhibition of Babesia bovis growth is probably related to the inhibition of the parasite M17 aminopeptidase, probably involved in host hemoglobin degradation. Schistosoma mansoni M17 aminopeptidases inhibition may affect parasite development, since they could participate in hemoglobin degradation, surface membrane remodeling and eggs hatching. Toxoplasma gondii M17 aminopeptidase inhibition could attenuate parasite virulence, since it is apparently involved in the hydrolysis of cathepsin Cs- or proteasome-produced dipeptides and/or cell attachment/invasion processes. These data are relevant to validate these enzymes as targets.

Nanomedicine-based strategies to improve treatment of cutaneous leishmaniasis

Nanomedicine strategies were first adapted and successfully translated to clinical application for diseases, such as cancer and diabetes. These strategies would no doubt benefit unmet diseases needs as in the case of leishmaniasis. The latter causes skin sores in the cutaneous form and affects internal organs in the visceral form. Treatment of cutaneous leishmaniasis (CL) aims at accelerating wound healing, reducing scarring and cosmetic morbidity, preventing parasite transmission and relapse. Unfortunately, available treatments show only suboptimal effectiveness and none of them were designed specifically for this disease condition. Tissue regeneration using nano-based devices coupled with drug delivery are currently being used in clinic to address diabetic wounds. Thus, in this review, we analyse the current treatment options and attempt to critically analyse the use of nanomedicine-based strategies to address CL wounds in view of achieving scarless wound healing, targeting secondary bacterial infection and lowering drug toxicity.

AKT Isoforms as a Target in Cancer and Immunotherapy

Over the past years, targeted therapies have received tremendous attention in cancer therapy. One of the most frequently targeted pathways is the PI3K/AKT/mTOR signaling pathway that regulates crucial cellular processes including proliferation, survival, and migration. In a wide variety of cancer entities, the PI3K/AKT/mTOR signaling pathway was found to be a critical driver of disease progression, indicating a noteworthy target in cancer therapy. This chapter focuses on targeted therapies against AKT, which is a key enzyme within the PI3K/AKT/mTOR pathway. Although the three different isoforms of AKT, namely AKT1, AKT2, and AKT3, have a high homology, the isoforms exhibit different biological functions. Recently, direct inhibitors against all AKT isoforms as well as selective inhibitors against specific AKT isoforms have been extensively investigated in preclinical work as well as in clinical trials to attenuate proliferation of cancer cells. While no AKT inhibitor has been approved by the FDA for cancer therapy to date, AKT still plays a crucial role in a variety of treatment strategies including immune checkpoint inhibition. In this chapter, we summarize the status of AKT inhibitors either targeting all or specific AKT isoforms. Furthermore, we explain the role of AKT signaling in direct inhibition of tumor cell growth as well as in immune cells and immune checkpoint inhibition.

Advances in Understanding Leishmania Pathobiology: What Does RNA-Seq Tell Us?

Leishmaniasis is a vector-borne disease caused by a protozoa parasite from over 20 Leishmania species. The clinical manifestations and the outcome of the disease vary greatly. Global RNA sequencing (RNA-Seq) analyses emerged as a powerful technique to profile the changes in the transcriptome that occur in the Leishmania parasites and their infected host cells as the parasites progresses through their life cycle. Following the bite of a sandfly vector, Leishmania are transmitted to a mammalian host where neutrophils and macrophages are key cells mediating the interactions with the parasites and result in either the elimination the infection or contributing to its proliferation. This review focuses on RNA-Seq based transcriptomics analyses and summarizes the main findings derived from this technology. In doing so, we will highlight caveats in our understanding of the parasite’s pathobiology and suggest novel directions for research, including integrating more recent data highlighting the role of the bacterial members of the sandfly gut microbiota and the mammalian host skin microbiota in their potential role in influencing the quantitative and qualitative aspects of leishmaniasis pathology.

Knowledge, attitude and practices towards visceral leishmaniasis among HIV patients: A cross-sectional study from Bihar, India

Background

In the Indian state of Bihar, visceral leishmaniasis (VL) is a major public health issue that has been aggravated by the rising incidence of new Human immunodeficiency virus (HIV) infections. In endemic areas, the risk of VL infections in patients living with HIV (PLHIV) is higher. It is important to investigate the disease-related knowledge, attitude, and practices (KAP) of PLHIV in Bihar in order to monitor HIV/VL co-infection. Adequate knowledge, a positive attitude, and good practices for VL control are essential to stamp out the disease. This study investigated the KAP towards VL in HIV patients attending antiretroviral therapy (ART) clinic at ICMR-RMRIMS, Patna.

Methods

A questionnaire based cross-sectional study was performed among 120 HIV patients aged ≥18 years, to evaluate their KAP regarding visceral leishmaniasis. For the KAP indicators, each correct answer received a score of 1, while unsure and incorrect responses received a score of 0. Descriptive statistics and logistic regression were used for the analysis. Data analysis was performed using Statistical Package for the Social Sciences (SPSS) version 27.

Results

The study population had a male (68.30%) preponderance with a mean age of 37.03 years ± 9.80 years of standard deviation. The majority (93.30%) of the study participants had previously heard about VL. Only 32.10% of those who had heard about VL knew that the disease was transmitted by the sandfly. Most (80.40%) of the study respondents were ignorant of the sandfly breeding grounds. The vast majority (75.90%) had no idea how to recognize sandflies and were unaware of their biting time, leishmaniasis transmission season, and preventive practices. Although PLHIV are vulnerable to VL, only 27.70% of them agreed that VL is a fatal disease if untreated, and 42.90% believed they wear not at risk of developing the disease. Regarding the control methods of sandflies, 28.60% of participants did not use any methods to avoid sandfly bites. The multivariable analysis revealed that occupation and family history were the two independent predictor variables of the knowledge index. Age and gender were significantly associated with attitude towards VL. Participants working as laborers had significantly lesser odds (AOR: 0.248, 95% CI: 0.073–0.844) to follow good preventive practices. There were significantly higher odds of having good practice among participants aged 18–40 years (AOR: 6.866, 95% CI: 1.694–27.834) and those residing in urban areas (AOR: 4.159, 95% CI: 1.317–13.139) than their peers. Overall, 27.7% of respondents were knowledgeable, 41.1% had a positive mindset, and 33.9% had strong VL preventive habits, according to the study.

Conclusion

The study determined a remarkable gap in the knowledge attitude and practices towards VL among PLHIV. This underscores the need of augmented health education initiatives for PLHIV in endemic areas for good VL awareness and preventive practices.

In vitro and in vivo antileishmanial activity of β-acetyl-digitoxin, a cardenolide of Digitalis lanata potentially useful to treat visceral leishmaniasis

Current treatments of visceral leishmaniasis face limitations due to drug side effects and/or high cost, along with the emergence of parasite resistance. Novel and low-cost antileishmanial agents are therefore required. We report herein the antileishmanial activity of β-acetyl-digitoxin (b-AD), a cardenolide isolated from Digitalis lanata leaves, assayed in vitro and in vivo against Leishmania infantum. Results showed direct action of b-AD against parasites, as well as efficacy for the treatment of Leishmania-infected macrophages. In vivo experiments using b-AD-containing Pluronic^® F127 polymeric micelles (b-AD/Mic) to treat L. infantum-infected mice showed that this composition reduced the parasite load in distinct organs in more significant levels. It also induced the development of anti-parasite Th1-type immunity, attested by high levels of IFN-γ, IL-12, TNF-α, GM-CSF, nitrite and specific IgG2a antibodies, in addition to low IL-4 and IL-10 contents, along with higher IFN-γ-producing CD4⁺ and CD8⁺ T-cell frequency. Furthermore, low toxicity was found in the organs of the treated animals. Comparing the therapeutic effect between the treatments, b-AD/Mic was the most effective in protecting animals against infection, when compared to the other groups including miltefosine used as a drug control. Data found 15 days after treatment were similar to those obtained one day post-therapy. In conclusion, the results obtained suggest that b-AD/Mic is a promising antileishmanial agent and deserves further studies to investigate its potential to treat visceral leishmaniasis.

Efficacy of Spironolactone Treatment in Murine Models of Cutaneous and Visceral Leishmaniasis

Translational studies involving the reuse and association of drugs are approaches that can result in higher success rates in the discovery and development of drugs for serious public health problems, including leishmaniasis. If we consider the number of pathogenic species in relation to therapeutic options, this arsenal is still small, and each drug possesses a disadvantage in terms of toxicity, efficacy, price, or treatment regimen. In the search for new drugs, we performed a drug screening of L. amazonensis promastigotes and intracellular amastigotes of fifty available drugs belonging to several classes according to their pharmacophoric group. Spironolactone, a potassium-sparing diuretic, proved to be the most promising drug candidate. After demonstrating the in vitro antileishmanial activity, we evaluated the efficacy on a murine experimental model with L. amazonensis and L. infantum. The treatment controlled the cutaneous lesion and reduced the parasite burden of L. amazonensis significantly, as effectively as meglumine antimoniate. The treatment of experimental visceral leishmaniasis was effective in reducing the parasite load on the main affected organs (spleen and liver) via high doses of spironolactone. The association between spironolactone and meglumine antimoniate promoted better control of the parasite load in the spleen and liver compared to the group treated with meglumine antimoniate alone. These results reveal a possible benefit of the concomitant use of spironolactone and meglumine antimoniate that should be studied more in depth for the future possibility of repositioning for leishmaniasis co-therapy.

Revisiting nature: a review of iridoids as a potential antileishmanial class

Leishmaniasis still stands as one of the most prevalent neglected tropical diseases in the least developed and emerging countries. The recommended therapeutic arsenal to treat leishmaniasis is characterized by several shortcomings, and resistance has already been reported. Hence, this dramatic background highlights the pressing need to develop novel, affordable, and safe antileishmanial drugs. Multiple classes of natural compounds have been reported to possess antileishmanial activity. Among these classes, iridoids stand out as a special type of monoterpenoids with diverse biological properties-including their antileishmanial potential. This review aims to discuss the available literature between 1991 and 2020 related to the antileishmanial activity of the iridoid class. Throughout the past decades, various investigations attributed antileishmanial action to assorted iridoid types, including inhibitory potential towards validated drug targets and immunomodulatory activity. The latter deserves special attention due to the ability of some iridoids to improve the host's immune response against parasites. It opens the possibility of iridoids become adjuncts in leishmaniasis treatments by improving the efficacy of currently employed drugs. Furthermore, the present study intends to provide a convenient visual representation of which iridoids and Leishmania spp. species have been most investigated as a guide for further researches.

An immunoprophylactic evaluation of Ld-ODC derived HLA-A0201 restricted peptides against visceral leishmaniasis

Five (5) HLA-A 0201 restricted epitopes of ornithine decarboxylase derived from Leishmania donovani (Ld-ODC) were examined by reverse vaccinology to develop prophylactics against visceral leishmaniasis (VL). These consensus epitopes comprising (P1: RLMPSAHAI, P2: LLDQYQIHL, P3: GLYHSFNCI, P4: AVLEVLSAL and P5: RLPASPAAL) were observed and presented by diverse HLA alleles screened by immune-informatics tools. These epitopes were also observed for strong stability for appropriate immune response in in silico screening and molecular dynamics. Top five selected epitopes filtered from population coverage analysis and TAP binding affinity were identified and evaluated against treated cases of VL subjects. Experiments were run individually with synthetic peptides or as the cocktail of peptides. A major population of CD8+ T cells were predominantly IFN-γ producers but not the IL-10 cytokines and shown with granzyme-B activity. Therefore, it can be concluded that the screened HLA-A0201 restricted epitope hotspots derived from Leishmania ODC can trigger CD8+ T cells, which can skew other immune cells functions toward protection. However, a detailed analysis can explore its potentiality as a vaccine candidate.Communicated by Ramaswamy H. Sarma.

Therapeutic Modalities in Post Kala-azar Dermal Leishmaniasis: A Systematic Review of the Effectiveness and Safety of the Treatment Options

Post-kala-azar dermal Leishmaniasis (PKDL) is one of the important neglected tropical diseases, which has a tremendous epidemiological significance, being the reservoir of kala-azar. Relapse and resistance to treatment along with the lack of a drug of choice and consensus treatment guideline pose a significant problem in the management of PKDL. The aim of this article was to review the available therapeutic options for PKDL, with special emphasis on their pharmaco-dynamics, pharmaco-kinetics, effectiveness, safety, tolerability, and cost factor. A comprehensive English language literature search was done for therapeutic options in PKDL across multiple databases (PubMed, EMBASE, MEDLINE, and Cochrane) for keywords (alone and in combination). MeSH as well as non-MeSH terms such as “Kala-azar,” “Leishmaniasis” AND “Treatment,” “Management,” “Antimony Sodium Gluconate,” “Meglumine Antimoniate,” “Amphotericin B,” “Paromomycin,” “Miltefosine” were taken into consideration. Among 576 relevant articles, 15 were deemed relevant to this review. These articles were evaluated using “Oxford Centre for Evidence-Based Medicine (OCEBM)” AND “strength of recommendation taxonomy” (SORT) with respect to the level of evidence and grade of recommendation. The review includes 15 studies. The use of sodium stibogluconate is being discouraged because of multiple documented reports of treatment failure. Liposomal amphotericin B is emerging as a favorable option, owing to its superiority in terms of effectiveness and safety profile. Miltesfosine is the drug of choice in India because of the ease of oral administration and minimal risk of toxicity. Isolated Paromomycin alone is not effective in PKDL; however, combination therapy with sodium stibogluconate is found to be safe and effective. Combination of amphotericin B and miltefosine is one of the excellent options. Immunotherapy with combination of alum-precipitated autoclaved Leishmania major (Alum/ALM) vaccine + Bacille Calmette-Gu´erin (BCG) has shown promising results. Kala-azar continues to haunt the tropical countries and PKDL being its reservoir is threatening its elimination. With the availability of drugs such as liposomal amphotericin B and miltefosine, apart from the advent of immunotherapy, the future of treatment of this condition looks promising.

Gallic and Ellagic Acids Are Promising Adjuvants to Conventional Amphotericin B for the Treatment of Cutaneous Leishmaniasis

In this study, we demonstrated the potential associative effect of combining conventional amphotericin B (Amph B) with gallic acid (GA) and with ellagic acid (EA) in topical formulations for the treatment of cutaneous leishmaniasis in BALB/c mice. Preliminary stability tests of the formulations and in vitro drug release studies with Amph B, GA, Amph B plus GA, EA, and Amph B plus EA were carried out, as well as assessment of the in vivo treatment of BALB/c mice infected with Leishmania major After 40 days of infection, the animals were divided into 6 groups and treated twice a day for 21 days with a gel containing Amph B, GA, Amph B plus GA, EA, or Amph B plus EA, and the negative-control group was treated with the vehicle. In the animals that received treatment, there was reduction of the lesion size and reduction of the parasitic load. Histopathological analysis of the treatments with GA, EA, and combinations with Amph B showed circumscribed lesions with the presence of fibroblasts, granulation tissue, and collagen deposition, as well as the presence of activated macrophages. The formulations containing GA and EA activated macrophages in all evaluated parameters, resulting in the activation of cells of the innate immune response, which can generate healing and protection. GA and EA produced an associative effect with Amph B, which makes them promising for use with conventional Amph B in the treatment of cutaneous leishmaniasis.

Recuperating Biopharmaceutical Aspects of Amphotericin B and Paromomycin Using a Chitosan Functionalized Nanocarrier via Oral Route for Enhanced Anti-leishmanial Activity

The design and development of new pharmaceutical formulations for the existing anti-leishmanial is a new strategic alternate to improve efficacy and safety rather than new drug discovery. Herein hybrid solid lipid nanoparticles (SLN) have been engineered to direct the oral delivery of two anti-leishmanial drugs amphotericin B (AmB) and paromomycin (PM). The combinatorial nanocarriers consist of conventional SLN, antileishmanial drugs (AmB and PM) which have been functionalized with chitosan (Cs) grafted onto the external surface. The Cs-SLN have the mean particle size of 373.9 ± 1.41 nm, polydispersity index (PDI) of 0.342 ± 0.02 and the entrapment efficiency for AmB and PM was found to be 95.20 ± 3.19% and 89.45 ± 6.86 %, respectively. Characterization of SLN was performed by scanning electron microscopy and transmission electron microscopy. Complete internalization of the formulation was observed in Caco-2 cells. Cs-SLN has shown a controlled and slow drug release profile over a period of 72 h and was stable at gastrointestinal fluids, confirmed by simulated gastro-intestinal fluids study. Cs coating enhanced the mucoadhesive property of Cs-SLN. The in-vitro anti-leishmanial activity of Cs-SLN (1 μg/ml) has shown a maximum percentage of inhibition (92.35%) on intra-cellular amastigote growth of L. donovani.

Nano-co-delivery of lipophosphoglycan with soluble and autoclaved leishmania antigens into PLGA nanoparticles: Evaluation of in vitro and in vivo immunostimulatory effects against visceral leishmaniasis

The aim of the present study was to encapsulate lipophosphoglycan molecule (LPG) which is one of the most immunogenic antigens of Leishmania parasites into PLGA nanoparticles with autoclaved or soluble leishmanial antigens, characterize synthetized nanoparticles with different methods and evaluate their in vitro/in vivo immunostimulatory activities to develop new vaccine candidates. PLGA nanoparticles including LPG and autoclaved leishmania antigen (ALA) or soluble leishmania antigen (ALA) were synthetized by double emulsion solvent evaporation method. The synthetized nanoparticles were characterized by SEM and Zeta-sizer instruments for determination of size, zeta potentials and polydispersity index (PDI) values. The antigen release profiles and encapsulation efficiencies were determined by UV-Vis spectroscopy. Griess reaction and ELISA tests were used for measurements of produced nitric oxide (NO) and cytokine levels of macrophages and splenocytes treated with nanoparticles. For determination of protective effects of nanoparticles, parasite reduction in livers and spleens of immunized mice were calculated by LDU values post-infection. According to results, (SLA-LPG) PLGA NPs and (ALA-LPG) PLGA NPs possessed the sizes of 253 and 307 nm respectively. Antigen-loaded nanoparticles elevated the released NO amounts from macrophages for 14 and 18-folds in contrast to control. Furthermore, synthetized nanoparticles significantly triggered macrophages to produce excessive levels of IFN-γ and IL-12 cytokines. Besides it was detected that vaccination of mice with (SLA-LPG) PLGA NPs and (ALA-LPG) PLGA NPs elicited approximately 80% protection from Visceral Leishmaniasis. Furthermore, (SLA-LPG) PLGA NPs and (ALA-LPG) PLGA NPs lead to 10 to 14-folds increase in secreted Th1 cytokine levels from splenocytes than control demonstrating abundantly stimulation of T cell response following to vaccination with nano-vaccine formulations. These results reveal that both (SLA-LPG) PLGA NPs and (ALA-LPG) PLGA NPs have excellent immunostimulatory activities and they are promising nanovaccine formulations for the prevention of leishmaniasis in near future.

Parasitological and immunological evaluation of a novel chemotherapeutic agent against visceral leishmaniasis

AIMS

Treatment for visceral leishmaniasis (VL) is hampered by the toxicity and/or high cost of drugs, as well as by emergence of parasite resistance. Therefore, there is an urgent need for new antileishmanial agents.

METHODS AND RESULTS

In this study, the antileishmanial activity of a diprenylated flavonoid called 5,7,3,4'-tetrahydroxy-6,8-diprenylisoflavone (CMt) was tested against Leishmania infantum and L amazonensis species. Results showed that CMt presented selectivity index (SI) of 70.0 and 165.0 against L infantum and L amazonensis promastigotes, respectively, and of 181.9 and 397.8 against respective axenic amastigotes. Amphotericin B (AmpB) showed lower SI values of 9.1 and 11.1 against L infantum and L amazonensis promastigotes, respectively, and of 12.5 and 14.3 against amastigotes, respectively. CMt was effective in the treatment of infected macrophages and caused alterations in the parasite mitochondria. L infantum-infected mice treated with miltefosine, CMt alone or incorporated in polymeric micelles (CMt/Mic) presented significant reductions in the parasite load in distinct organs, when compared to the control groups. An antileishmanial Th1-type cellular and humoral immune response were developed one and 15 days after treatment, with CMt/Mic-treated mice presenting a better protective response.

CONCLUSION

Our data suggest that CMt/Mic could be evaluated as a chemotherapeutic agent against VL.

Antileishmanial Aminopyrazoles: Studies into Mechanisms and Stability of Experimental Drug Resistance

Current antileishmanial treatment is hampered by limitations, such as drug toxicity and the risk of treatment failure, which may be related to parasitic drug resistance. Given the urgent need for novel drugs, the Drugs for Neglected Diseases initiative (DNDi) has undertaken a drug discovery program, which has resulted in the identification of aminopyrazoles, a highly promising antileishmanial chemical series. Multiple experiments have been performed to anticipate the propensity for resistance development.

Current antileishmanial treatment is hampered by limitations, such as drug toxicity and the risk of treatment failure, which may be related to parasitic drug resistance. Given the urgent need for novel drugs, the Drugs for Neglected Diseases initiative (DNDi) has undertaken a drug discovery program, which has resulted in the identification of aminopyrazoles, a highly promising antileishmanial chemical series. Multiple experiments have been performed to anticipate the propensity for resistance development. Resistance selection was performed by successive exposure of Leishmania infantum promastigotes (in vitro) and intracellular amastigotes (both in vitro and in golden Syrian hamsters). The stability of the resistant phenotypes was assessed after passage in mice and Lutzomyia longipalpis sandflies. Whole-genome sequencing (WGS) was performed to identify mutated genes, copy number variations (CNVs), and somy changes. The potential role of efflux pumps (the MDR and MRP efflux pumps) in the development of resistance was assessed by coincubation of aminopyrazoles with specific efflux pump inhibitors (verapamil, cyclosporine, and probenecid). Repeated drug exposure of amastigotes did not result in the emergence of drug resistance either in vitro or in vivo. Selection at the promastigote stage, however, was able to select for parasites with reduced susceptibility (resistance index, 5.8 to 24.5). This phenotype proved to be unstable after in vivo passage in mice and sandflies, suggesting that nonfixed alterations are responsible for the elevated resistance. In line with this, single nucleotide polymorphisms and indels identified by whole-genome sequencing could not be directly linked to the decreased drug susceptibility. Copy number variations were absent, whereas somy changes were detected, which may have accounted for the transient acquisition of resistance. Finally, aminopyrazole activity was not influenced by the MDR and MRP efflux pump inhibitors tested. The selection performed does not suggest the rapid development of resistance against aminopyrazoles in the field. Karyotype changes may confer elevated levels of resistance, but these do not seem to be stable in the vertebrate and invertebrate hosts. MDR/MRP efflux pumps are not likely to significantly impact the activity of the aminopyrazole leads.

A candidate vaccine for human visceral leishmaniasis based on a specific T cell epitope-containing chimeric protein protects mice against Leishmania infantum infection

Leishmaniases are neglected diseases caused by infection with Leishmania parasites and there are currently no prophylactic vaccines. In this study, we designed in silico a synthetic recombinant vaccine against visceral leishmaniasis (VL) called ChimeraT, which contains specific T-cell epitopes from Leishmania Prohibitin, Eukaryotic Initiation Factor 5a and the hypothetical LiHyp1 and LiHyp2 proteins. Subcutaneous delivery of ChimeraT plus saponin stimulated a Th1 cell-mediated immune response and protected mice against L. infantum infection, significantly reducing the parasite load in distinct organs. ChimeraT/saponin vaccine stimulated significantly higher levels of IFN-γ, IL-12, and GM-CSF cytokines by both murine CD4⁺ and CD8⁺ T cells, with correspondingly low levels of IL-4 and IL-10. Induced antibodies were predominantly IgG2a isotype and homologous antigen-stimulated spleen cells produced significant nitrite as a proxy for nitric oxide. ChimeraT also induced lymphoproliferative responses in peripheral blood mononuclear cells from VL patients after treatment and healthy subjects, as well as higher IFN-γ and lower IL-10 secretion into cell supernatants. Thus, ChimeraT associated with a Th1 adjuvant could be considered as a potential vaccine candidate to protect against human disease.

Modeling and simulation study to identify threonine synthase as possible drug target in Leishmania major

Leishmaniasis is one of the most neglected tropical diseases that demand immediate attention to the identification of new drug targets and effective drug candidates. The present study demonstrates the possibility of using threonine synthase (TS) as a putative drug target in leishmaniasis disease management. We report the construction of an effective homology model of the enzyme that appears to be structurally as well as functionally well conserved. The 200 nanosecond molecular dynamics data on TS with and without pyridoxal phosphate (PLP) shed light on mechanistic details of PLP-induced conformational changes. Moreover, we address some important structural and dynamic interactions in the PLP binding region of TS that are in good agreement with previously speculated crystallographic estimations. Additionally, after screening more than 44,000 compounds, we propose 10 putative inhibitor candidates for TS based on virtual screening data and refined Molecular Mechanics Generalized Born Surface Area calculations. We expect that structural and functional dynamics data disclosed in this study will help initiate experimental endeavors toward establishing TS as an effective antileishmanial drug target.

Can We Harness Immune Responses to Improve Drug Treatment in Leishmaniasis?

Leishmaniasis is a vector-borne parasitic disease that has been neglected in priority for control and eradication of malaria, tuberculosis, and HIV/AIDS. Collectively, over one seventh of the world’s population is at risk of being infected with 0.7–1.2 million new infections reported annually. Clinical manifestations range from self-healing cutaneous lesions to fatal visceral disease. The first anti-leishmanial drugs were introduced in the 1950′s and, despite several shortcomings, remain the mainstay for treatment. Regardless of this and the steady increase in infections over the years, particularly among populations of low economic status, research on leishmaniasis remains under funded. This review looks at the drugs currently in clinical use and how they interact with the host immune response. Employing chemoimmunotherapeutic approaches may be one viable alternative to improve the efficacy of novel/existing drugs and extend their lifespan in clinical use.

Evaluation of the protective efficacy of a Leishmania protein associated with distinct adjuvants against visceral leishmaniasis and in vitro immunogenicity in human cells

The treatment against visceral leishmaniasis (VL) presents problems, mainly related to the toxicity and/or high cost of the drugs. In this context, a prophylactic vaccination is urgently required. In the present study, a Leishmania protein called LiHyE, which was suggested recently as an antigenic marker for canine and human VL, was evaluated regarding its immunogenicity and protective efficacy in BALB/c mice against Leishmania infantum infection. In addition, the protein was used to stimulate peripheral blood mononuclear cells (PBMCs) from VL patients before and after treatment, as well as from healthy subjects. Vaccination results showed that the recombinant (rLiHyE) protein associated with liposome or saponin induced effective protection in the mice, since significant reductions in the parasite load in spleen, liver, draining lymph nodes, and bone marrow were found. The parasitological protection was associated with Th1-type cell response, since high IFN-γ, IL-12, and GM-CSF levels, in addition to low IL-4 and IL-10 production, were found. Liposome induced a better parasitological and immunological protection than did saponin. Experiments using PBMCs showed rLiHyE-stimulated lymphoproliferation in treated patients' and healthy subjects' cells, as well as high IFN-γ levels in the cell supernatant. In conclusion, rLiHyE could be considered for future studies as a vaccine candidate against VL.

Liposomal Formulation of ChimeraT, a Multiple T-Cell Epitope-Containing Recombinant Protein, Is a Candidate Vaccine for Human Visceral Leishmaniasis

Background: Leishmaniases are neglected diseases caused by infection with Leishmania parasites and there are no human vaccines in use routinely. The purpose of this study was to examine the immunogenicity of ChimeraT, a novel synthetic recombinant vaccine against visceral leishmaniasis (VL), incorporated into a human-compatible liposome formulation. Methods: BALB/c mice were immunized subcutaneously with ChimeraT/liposome vaccine, ChimeraT/saponin adjuvant, or ChimeraT/saline and immune responses examined in vitro and in vivo. Results: Immunization with the ChimeraT/liposome formulation induced a polarized Th1-type response and significant protection against L. infantum infection. ChimeraT/liposome vaccine stimulated significantly high levels of interferon (IFN)-γ, interleukin (IL)-12, and granulocyte macrophage-colony stimulating factor (GM-CSF) cytokines by both CD4 and CD8 T-cells, with correspondingly lower levels of IL-4 and IL-10 cytokines. Induced antibodies were predominantly IgG2a isotype, and homologous antigen-stimulated spleen cells produced significant nitrite as a proxy for nitric oxide (NO). Furthermore, we examined a small number of treated VL patients and found higher levels of circulating anti-ChimeraT protein IgG2 antibodies, compared to IgG1 levels. Conclusions: Overall, the liposomal formulation of ChimeraT induced a protective Th1-type immune response and thus could be considered in future studies as a vaccine candidate against human VL.

Bisphosphonate-Based Molecules as Potential New Antiparasitic Drugs

Neglected tropical diseases such as Chagas disease and leishmaniasis affect millions of people around the world. Both diseases affect various parts of the globe and drugs traditionally used in therapy against these diseases have limitations, especially with regard to low efficacy and high toxicity. In this context, the class of bisphosphonate-based compounds has made significant advances regarding the chemical synthesis process as well as the pharmacological properties attributed to these compounds. Among this spectrum of pharmacological activity, bisphosphonate compounds with antiparasitic activity stand out, especially in the treatment of Chagas disease and leishmaniasis caused by Trypanosoma cruzi and Leishmania spp., respectively. Some bisphosphonate compounds can inhibit the mevalonate pathway, an essential metabolic pathway, by interfering with the synthesis of ergosterol, a sterol responsible for the growth and viability of these parasites. Therefore, this review aims to present the information about the importance of these compounds as antiparasitic agents and as potential new drugs to treat Chagas disease and leishmaniasis.

Leishmaniasis diagnosis: an update on the use of parasitological, immunological and molecular methods

Diagnosis of leishmaniasis has always been a major challenge as its clinical features resemble some other commonly occurring diseases such as tuberculosis, typhoid, and malaria. Reliable laboratory methods become important for differential diagnosis. Demonstration of the parasites in stained preparations of bone marrow and splenic aspirates being risky and invasive is still the gold standard for diagnosis. Serological tests utilizing rapid immunochromatographic formats or rK39 in enzyme linked immune sorbent assay, immunoblotting, direct agglutination test have complications related to high proportions of positive asymptomatic individuals and the inability to diagnose a relapse. Among the molecular techniques, polymerase chain reaction is the most commonly used technique that is successfully implied for diagnosis. This review provides updated information on the recent developments in the field of diagnosis in leishmaniasis, various methods utilized with their advantages and limitations.

A clioquinol-containing Pluronic® F127 polymeric micelle system is effective in the treatment of visceral leishmaniasis in a murine model

A clioquinol (ICHQ)-containing Pluronic^® F127 polymeric micelle system (ICHQ/Mic) was recently shown to be effective against Leishmania amazonensis infection in a murine model. In the present study, ICHQ/Mic was tested against L. infantum infection. BALB/c mice (n = 12 per group) were infected with L. infantum stationary promastigotes through subcutaneous injection and, 45 days after challenge, received saline or were treated via the subcutaneous route with empty micelles, ICHQ or ICHQ/Mic. In addition, animals were treated with miltefosine by the oral route, as a drug control. Half of the animals were euthanized 1 and 15 days after treatment, aiming to evaluate two endpoints after therapy, when parasitological and immunological parameters were investigated. Results showed that the treatment using miltefosine, ICHQ or ICHQ/Mic induced significantly higher anti-parasite IFN-γ, IL-12, GM-CSF, nitrite and IgG2a isotype antibody levels, which were associated with low IL-4 and IL-10 production. In addition, a higher frequency of IFN-γ and TNF-α-producing CD4⁺ and CD8⁺ T-cells was found in these animals. The parasite load was evaluated in distinct organs, and results showed that the treatment using miltefosine, ICHQ or ICHQ/Mic induced significant reductions in organic parasitism in the treated and infected mice. A comparison between the treatments suggested that ICHQ/Mic was the most effective in inducing a highly polarized Th1-type response, as well as reducing the parasite load in significant levels in the treated and infected animals. Data obtained 15 days after treatment suggested maintenance of the immunological and parasitological responses. In conclusion, ICHQ/Mic could be considered in future studies for the treatment of visceral leishmaniasis.

Phenotypical Characterization of Spleen Remodeling in Murine Experimental Visceral Leishmaniasis

Background: Visceral leishmaniasis (VL) is caused by Leishmania infantum or L. donovani infection. One of the main problems related to this disease is the emergence of severe clinical forms with a lethality of 5–20%, even while under specific treatment. In humans and other species susceptible to fatal VL, such as dogs and hamsters, the disruption of splenic white pulp (WP) is accompanied by disease progression. Control of VL progression is seen in BALB/c mice, as evidenced by a mild clinical presentation and controlled parasite replication in the liver and spleen. In this study, we investigated the features involved in the morphological remodeling of splenic compartments associated with the control of VL progression to death.

Methods: We evaluated cohorts of BALB/c mice after 30, 60, and 90 days of infection by L. infantum. Spleen morphology, cell population subsets and cytokine production were studied in the spleen using flow- and histo-cytometry.

Results: Intraperitoneal infection with 10⁸ promastigotes of L. infantum led to progressive increases in spleen size at 60 and 90 days after infection. Splenomegaly was the only clinical sign of disease observed. At 30 days after infection, hyperplasia in the WP and decreased numbers of plasmacytoid dendritic cells were observed. The WP hyperplasia subsided at 60 days post-infection. However, the splenomegaly remained in association with increased numbers of macrophages, B and T lymphocytes and plasma cells. An increased number of lymphoid tissue inducer (LTi) cells was observed; these were distributed around the periarteriolar lymphoid sheath in control mice and scattered throughout the red pulp in the Leishmania-infected mice. After 90 days of infection, increased IL-6 and IFN-γ production was seen in the spleen, as well as higher frequencies of follicular and plasmacytoid dendritic cells.

Conclusion: The data presented herein emphasizes the potential role of spleen remodeling in the control of severe forms of VL and highlights features potentially involved in this process.

The preclinical discovery and development of oral miltefosine for the treatment of visceral leishmaniasis: a case history

INTRODUCTION

Visceral leishmaniasis (VL) is a vector-borne disease caused by Leishmania donovani or Leishmania infantum. Closely related to poverty, VL is fatal and represents one of the main burdens on public health in developing countries. Treatment of VL relies exclusively on chemotherapy, a strategy still experiencing numerous limitations. Miltefosine (MF) has been used in the chemotherapy of VL in some endemic areas, and has been expanded to other regions, being considered crucial in eradication programs.

AREAS COVERED

This article reviews the most relevant preclinical and clinical aspects of MF, its mechanism of action and resistance to Leishmania parasites, as well as its limitations. The authors also give their perspectives on the treatment of VL.

EXPERT OPINION

The discovery of MF represented an enormous advance in the chemotherapy of VL, since it was the first oral drug for this neglected disease. Beyond selection of resistant parasites due to drug pressure, several other factors can lead to treatment failure such as, for example, factors intrinsic to the host, parasite and the drug itself. Although its efficacy as a monotherapy has reduced over recent years, MF is still an important alternative in VL chemotherapy, especially when used in combination with other drugs.

Detection and functional characterization of sigma class GST in Phlebotomus argentipes and its role in stress tolerance and DDT resistance

Several Glutathione S-transferases (GSTs) enzymes, in insects, have previously been implicated in resistance developed against DDT and other insecticides. The GST enzyme particularly sigma class have important physiological role in detoxification of lipid peroxidation by-products in insects. Phlebotomus argentipes has been intensely exposed to DDT over years due to Indoor Residual Spray (IRS) programme for Kala-azar elimination in Bihar, India. However, in P. argentipes, role of GSTs in DDT resistance have not been elucidated. Here, sigma class GST of P. argentipes (Parg-GSTσ) was successfully cloned, expressed and purified by affinity chromatography. The recombinant Parg-GSTσ was found to be highly active towards cumene hydroperoxide and 4-HNE having specific activity 92.47 & 203.92 µM/min/mg of protein, respectively and exhibited low activity towards universal substrate CDNB i.e., 8.75 µM/min/mg of protein. RT-PCR and immunoblot analysis showed at least 2 and 1.8 fold overexpression of Parg-GSTσ in the single exposed and non exposed DDT resistant P. argentipes as compared to susceptible, implicating Parg-GSTσ also involved in DDT resistance probably by imparting enhanced stress tolerance. The DDT, H₂O₂ and temperature induction assays demonstrated stress-dependent induction of Parg-GSTσ expression indicating its important role in oxidative stress redressal.

Genomic and Metabolomic Polymorphism among Experimentally Selected Paromomycin-Resistant Leishmania donovani Strains

Understanding the mechanism(s) underpinning drug resistance could lead to novel treatments to reverse the increased tolerance of a pathogen. In this study, paromomycin (PMM) resistance (PMM^r) was induced in three Nepalese clinical strains of Leishmania donovani with different inherent susceptibilities to antimony (Sb) drugs by stepwise exposure of promastigotes to PMM.

Understanding the mechanism(s) underpinning drug resistance could lead to novel treatments to reverse the increased tolerance of a pathogen. In this study, paromomycin (PMM) resistance (PMM^r) was induced in three Nepalese clinical strains of Leishmania donovani with different inherent susceptibilities to antimony (Sb) drugs by stepwise exposure of promastigotes to PMM. Exposure to PMM resulted in the production of mixed populations of parasites, even though a single cloned population was used at the start of selection. PMM 50% inhibitory concentration (IC₅₀) values for PMM^r parasites varied between 104 and 481 μM at the promastigote stage and 32 and 195 μM at the intracellular amastigote stage. PMM resistance was associated with increased resistance to nitric oxide at the amastigote stage but not the promastigote stage (P < 0.05). This effect was most marked in the Sb-resistant (Sb^r) PMM^r clone, in which PMM resistance was associated with a significant upregulation of glutathione compared to that in its wild type (P < 0.05), although there was no change in the regulation of trypanothione (detected in its oxidized form). Interestingly, PMM^r strains showed an increase in either the keto acid derivative of isoleucine (Sb intermediate PMM^r) or the 2-hydroxy acids derived from arginine and tyrosine (Sb susceptible PMM^r and Sb^r PMM^r). These results are consistent with the recent finding that the upregulation of the branched-chain amino acid aminotransferase and d-lactate dehydrogenase is linked to PMM^r. In addition, we found that PMM^r is associated with a significant increase in aneuploidy during PMM selection in all the strains, which could allow the rapid selection of genetic changes that confer a survival advantage.

Visceral Leishmaniasis Treatment Outcome and Associated Factors in Northern Ethiopia

BACKGROUND

Visceral leishmaniasis (VL), one of the most neglected tropical diseases, is placing a huge burden on Ethiopia. Despite the introduction of antileishmanial drugs, treatment outcomes across regions are variable due to drug resistance and other factors. Thus, understanding of VL treatment outcomes and its contributing factors helps decisions on treatment. However, the magnitude and the risk factors of poor treatment outcome are not well studied in our setting. Therefore, our study was designed to assess treatment outcomes and associated factors in patients with VL.

MATERIALS AND METHODS

A cross-sectional study was conducted in VL patients admitted between June 2016 and April 2018 to Ayder Comprehensive Specialized Hospital, Tigray, Northern Ethiopia. Data was collected through chart review of patient records. Logistic regression analysis was used to identify factors associated with poor treatment outcome.

RESULTS

A total of 148 VL patients were included in the study. The mean age (SD) of the patients was 32.86 (11.9) years; most of them (94.6%) were male patients. The proportion of poor treatment outcome was 12.1%. Multivariable logistic regression analysis showed that long duration of illness (> four weeks) (adjusted odds ratio (AOR): 6.1 [95% confidence interval (CI); 1.3-28.6], p=0.02) and concomitant tuberculosis (TB) infection (AOR 4.6 [95% CI; 1.1-19.1], p=0.04) were the independent predictors of poor treatment outcome.

CONCLUSIONS

Poor treatment outcome was observed in a considerable proportion of VL patients. Long duration of illness and coinfection with TB were associated with poor VL treatment outcome. Hence, early diagnosis and effective prompt treatment are important to improve treatment outcomes among VL patients. Special attention should also be given in the treatment of VL/TB coinfected patients in our setting.

Transcriptional blood signatures for active and amphotericin B treated visceral leishmaniasis in India

Amphotericin B provides improved therapy for visceral leishmaniasis (VL) caused by Leishmania donovani, with single dose liposomal-encapsulated Ambisome providing the best cure rates. The VL elimination program aims to reduce the incidence rate in the Indian subcontinent to <1/10,000 population/year. Ability to predict which asymptomatic individuals (e.g. anti-leishmanial IgG and/or Leishmania-specific modified Quantiferon positive) will progress to clinical VL would help in monitoring disease outbreaks. Here we examined whole blood transcriptional profiles associated with asymptomatic infection, active disease, and in treated cases. Two independent microarray experiments were performed, with analysis focussed primarily on differentially expressed genes (DEGs) concordant across both experiments. No DEGs were identified for IgG or Quantiferon positive asymptomatic groups compared to negative healthy endemic controls. We therefore concentrated on comparing concordant DEGs from active cases with all healthy controls, and in examining differences in the transcriptome following different regimens of drug treatment. In these comparisons 6 major themes emerged: (i) expression of genes and enrichment of gene sets associated with erythrocyte function in active cases; (ii) strong evidence for enrichment of gene sets involved in cell cycle in comparing active cases with healthy controls; (iii) identification of IFNG encoding interferon-γ as the major hub gene in concordant gene expression patterns across experiments comparing active cases with healthy controls or with treated cases; (iv) enrichment for interleukin signalling (IL-1/3/4/6/7/8) and a prominent role for CXCL10/9/11 and chemokine signalling pathways in comparing active cases with treated cases; (v) the novel identification of Aryl Hydrocarbon Receptor signalling as a significant canonical pathway when comparing active cases with healthy controls or with treated cases; and (vi) global expression profiling support for more effective cure at day 30 post-treatment with a single dose of liposomal encapsulated amphotericin B compared to multi-dose non-liposomal amphotericin B treatment over 30 days. (296 words; 300 words allowed).

Envisioning the innovations in nanomedicine to combat visceral leishmaniasis: for future theranostic application

Visceral leishmaniasis (VL) is a life-threatening parasitic disease affecting impoverished people of the developing world; and much effort has been spent on the early case detection and treatment. However, current diagnostics and treatment options are not sufficient for appropriate surveillance in VL elimination setting. Hence, there is a dire need to develop highly sensitive diagnostics and less toxic effective treatments for proper management of cases and to achieve the sustained disease elimination. Although, promising results have been observed with nanomedicines in leishmaniasis; there are great challenges ahead especially in translating this to clinical setting. This review provides updated progress of nanomedicines in VL, and discussed how these innovations and future directions play vital role in achieving VL elimination.

GDP-Mannose Pyrophosphorylase: A Biologically Validated Target for Drug Development Against Leishmaniasis

Leishmaniases are neglected tropical diseases that threaten about 350 million people in 98 countries around the world. In order to find new antileishmanial drugs, an original approach consists in reducing the pathogenic effect of the parasite by impairing the glycoconjugate biosynthesis, necessary for parasite recognition and internalization by the macrophage. Some proteins appear to be critical in this way, and one of them, the GDP-Mannose Pyrophosphorylase (GDP-MP), is an attractive target for the design of specific inhibitors as it is essential for Leishmania survival and it presents significant differences with the host counterpart. Two GDP-MP inhibitors, compounds A and B, have been identified in two distinct studies by high throughput screening and by a rational approach based on molecular modeling, respectively. Compound B was found to be the most promising as it exhibited specific competitive inhibition of leishmanial GDP-MP and antileishmanial activities at the micromolar range with interesting selectivity indexes, as opposed to compound A. Therefore, compound B can be used as a pharmacological tool for the development of new specific antileishmanial drugs.

Casein-Conjugated Gold Nanoparticles for Amperometric Detection of Leishmania infantum

Sensitive and reliable approaches targeting the detection of Leishmania are critical for effective early diagnosis and treatment of leishmaniasis. In this frame, this paper describes a rapid quantification assay to detect Leishmania parasites based on the combination of the electrocatalytic ability of gold nanoparticles (AuNPs) to act as a catalyst for the hydrogen formation reaction along with the specificity of the interaction between casein and the major surface protease of the Leishmania parasite, GP63. First, pure and casein-modified AuNPs were prepared and characterized by scanning electron microscopy and ultraviolet-visible spectroscopy. Then, casein-conjugated AuNPs were incubated with Leishsmania parasites in solution; the formed complex was collected by centrifugation, treated by acidic solution, and the pelleted AuNPs were placed on screen-printed carbon electrodes (SPCEs) and chronoamperometric measurements were carried out. Our results suggest that it is possible to detect Leishmania parasites, with a limit less than 1 parasite/mL. A linear response over a wide concentration interval, ranging from 2 × 10^-2 to 2 × 10⁵ parasites/mL, was achieved. Additionally, a pretreatment of Leishmania parasites with Amphotericin B, diminished their interaction with casein. This findings and methodology are very useful for drug efficacy assessment.

Clinical Pharmacokinetics of Systemically Administered Antileishmanial Drugs

This review describes the pharmacokinetic properties of the systemically administered antileishmanial drugs pentavalent antimony, paromomycin, pentamidine, miltefosine and amphotericin B (AMB), including their absorption, distribution, metabolism and excretion and potential drug–drug interactions. This overview provides an understanding of their clinical pharmacokinetics, which could assist in rationalising and optimising treatment regimens, especially in combining multiple antileishmanial drugs in an attempt to increase efficacy and shorten treatment duration. Pentavalent antimony pharmacokinetics are characterised by rapid renal excretion of unchanged drug and a long terminal half-life, potentially due to intracellular conversion to trivalent antimony. Pentamidine is the only antileishmanial drug metabolised by cytochrome P450 enzymes. Paromomycin is excreted by the kidneys unchanged and is eliminated fastest of all antileishmanial drugs. Miltefosine pharmacokinetics are characterized by a long terminal half-life and extensive accumulation during treatment. AMB pharmacokinetics differ per drug formulation, with a fast renal and faecal excretion of AMB deoxylate but a much slower clearance of liposomal AMB resulting in an approximately ten-fold higher exposure. AMB and pentamidine pharmacokinetics have never been evaluated in leishmaniasis patients. Studies linking exposure to effect would be required to define target exposure levels in dose optimisation but have only been performed for miltefosine. Limited research has been conducted on exposure at the drug’s site of action, such as skin exposure in cutaneous leishmaniasis patients after systemic administration. Pharmacokinetic data on special patient populations such as HIV co-infected patients are mostly lacking. More research in these areas will help improve clinical outcomes by informed dosing and combination of drugs.

Tetraazamacrocyclic derivatives and their metal complexes as antileishmanial leads

A total of 44 bis-aryl-monocyclic polyamines, monoaryl-monocyclic polyamines and their transition metal complexes were prepared, chemically characterized, and screened in vitro against the Leishmania donovani promastigotes, axenic amastigotes and intracellular amastigotes in THP1 cells. The IC50 and/or IC90 values showed that 10 compounds were similarly active at about 2-fold less potent than known drug pentamidine against promastigotes. The most potent compound had an IC50 of 2.82 μM (compared to 2.93 μM for pentamidine). Nine compounds were 1.1-13.6-fold more potent than pentamidine against axenic amastigotes, the most potent one being about 2-fold less potent than amphotericin B. Fourteen compounds were about 2-10 fold more potent than pentamidine, the most potent one is about 2-fold less potent than amphotericin B against intracellular amastigotes in THP1 cells. The 2 most promising compounds (FeL7Cl2 and MnL7Cl2), with strong activity against both promastigotes and amastigotes and no observable toxicity against the THP1 cells are the Fe2+- and Mn2+- complexes of a dibenzyl cyclen derivative. Only 2 of the 44 compounds showed observable cytotoxicity against THP1 cells. Tetraazamacrocyclic monocyclic polyamines represent a new class of antileishmanial lead structures that warrant follow up studies.

Synthesis and Leishmanicidal Activity of Novel Urea, Thiourea, and Selenourea Derivatives of Diselenides

A novel series of thirty-one N-substituted urea, thiourea, and selenourea derivatives containing diphenyldiselenide entities were synthesized, fully characterized by spectroscopic and analytical methods, and screened for their in vitro leishmanicidal activities. The cytotoxic activity of these derivatives was tested against Leishmania infantum axenic amastigotes, and selectivity was assessed in human THP-1 cells. Thirteen of the synthesized compounds showed a significant antileishmanial activity, with 50% effective concentration (EC₅₀) values lower than that for the reference drug miltefosine (EC₅₀, 2.84 μM). In addition, the derivatives 9, 11, 42, and 47, with EC₅₀ between 1.1 and 1.95 μM, also displayed excellent selectivity (selectivity index ranged from 12.4 to 22.7) and were tested against infected macrophages. Compound 11, a derivative with a cyclohexyl chain, exhibited the highest activity against intracellular amastigotes, with EC₅₀ values similar to those observed for the standard drug edelfosine. Structure-activity relationship analyses revealed that N-aliphatic substitution in urea and selenourea is recommended for the leishmanicidal activity of these analogs. Preliminary studies of the mechanism of action for the hit compounds was carried out by measuring their ability to inhibit trypanothione reductase. Even though the obtained results suggest that this enzyme is not the target for most of these derivatives, their activity comparable to that of the standards and lack of toxicity in THP-1 cells highlight the potential of these compounds to be optimized for leishmaniasis treatment.

Assessment of quality of life using WHOQOL-BREF in patients with visceral leishmaniasis

BACKGROUND

This study was aimed to assess the impact of quality of life using WHOQOL-BREF in patients with Visceral leishmaniasis (VL).

METHODS

A total of 95 VL cases and 95 healthy participants filled out the questionnaires. Data on socio-demographic aspects along with disease duration were collected. Data were compared using a t-test, analysis of variance and chi-square test.

RESULTS

VL patients experienced very high impact on their quality of life. Study cohort had male preponderance (72.63%). Majority (64.21%) were aged < 40 years. Longer disease duration was found to have significantly poor quality of life (p < 0.05). The physical domain was found to be most affected domains of quality of life (QOL). QOL was affected most in illiterate, married, housewife, rural population and patients with longer disease duration (p < 0.05). The psychological and environmental domains were significantly affected in > 40 years of age group married patients (p < 0.05).

CONCLUSIONS

VL significantly impaired the patients' (QOL) in all four domains (physical, psychological, social relationship and environmental). Physical domain was significantly the most affected domain.

Druggable Targets in Cyclic Nucleotide Signaling Pathways in Apicomplexan Parasites and Kinetoplastids against Disabling Protozoan Diseases in Humans

Cell signaling in eukaryotes is an evolutionarily conserved mechanism to respond and adapt to various environmental changes. In general, signal sensation is mediated by a receptor which transfers the signal to a cascade of effector proteins. The cyclic nucleotides 3′,5′-cyclic adenosine monophosphate (cAMP) and 3′,5′-cyclic guanosine monophosphate (cGMP) are intracellular messengers mediating an extracellular stimulus to cyclic nucleotide-dependent kinases driving a change in cell function. In apicomplexan parasites and kinetoplastids, which are responsible for a variety of neglected, tropical diseases, unique mechanisms of cyclic nucleotide signaling are currently identified. Collectively, cyclic nucleotides seem to be essential for parasitic proliferation and differentiation. However, there is no a genomic evidence for canonical G-proteins in these parasites while small GTPases and secondary effector proteins with structural differences to host orthologues occur. Database entries encoding G-protein-coupled receptors (GPCRs) are still without functional proof. Instead, signals from the parasite trigger GPCR-mediated signaling in the host during parasite invasion and egress. The role of cyclic nucleotide signaling in the absence of G-proteins and GPCRs, with a particular focus on small GTPases in pathogenesis, is reviewed here. Due to the absence of G-proteins, apicomplexan parasites and kinetoplastids may use small GTPases or their secondary effector proteins and host canonical G-proteins during infection. Thus, the feasibility of targeting cyclic nucleotide signaling pathways in these parasites, will be an enormous challenge for the identification of selective, pharmacological inhibitors since canonical host proteins also contribute to pathogenesis.

Second-generation pterocarpanquinones: synthesis and antileishmanial activity

Background

Despite the development of new therapies for leishmaniasis, among the 200 countries or territories reporting to the WHO, 87 were identified as endemic for Tegumentary Leishmaniasis and 75 as endemic for Visceral Leishmaniasis. The identification of antileishmanial drug candidates is essential to fill the drug discovery pipeline for leishmaniasis. In the hit molecule LQB-118 selected, the first generation of pterocarpanquinones was effective and safe against experimental visceral and cutaneous leishmaniasis via oral delivery. In this paper, we report the synthesis and antileishmanial activity of the second generation of pterocarpanoquinones.

Methods

The second generation of pterocarpanquinones 2a-f was prepared through a palladium-catalyzed oxyarylation of dihydronaphtalen and chromens with iodolawsone, easily prepared by iodination of lawsone. The spectrum of antileishmanial activity was evaluated in promastigotes and intracellular amastigotes of L. amazonensis, L. braziliensis, and L. infantum. Toxicity was assessed in peritoneal macrophages and selective index calculated by CC₅₀/IC₅₀. Oxidative stress was measured by intracellular ROS levels and mitochondrial membrane potential in treated cells.

Results

In this work, we answered two pertinent questions about the structure of the first-generation pterocarpanquinones: the configuration and positions of rings B (pyran) and C (furan) and the presence of oxygen in the B ring. When rings B and C are exchanged, we noted an improvement of the activity against promastigotes and amastigotes of L. amazonensis and promastigotes of L. infantum. As to the oxygen in ring B of the new generation, we observed that the oxygenated compound 2b is approximately twice as active against L. braziliensis promastigotes than its deoxy derivative 2a. Another modification that improved the activity was the addition of the methylenedioxy group. A variation in the susceptibility among species was evident in the clinically relevant form of the parasite, the intracellular amastigote. L. amazonensis was the species most susceptible to novel derivatives, whilst L. infantum was resistant to most of them. The pterocarpanoquinones (2b and 2c) that possess the oxygen atom in ring B showed induction of increased ROS production.

Conclusions

The data presented indicate that the pterocarpanoquinones are promising compounds for the development of new leishmanicidal agents.

The leishmanicidal activity of artemisinin is mediated by cleavage of the endoperoxide bridge and mitochondrial dysfunction

Endoperoxides kill malaria parasites via cleavage of their endoperoxide bridge by haem or iron, leading to generation of cytotoxic oxygen-centred radicals. In view of the Leishmania parasites having a relatively compromised anti-oxidant defense and high iron content, this study aims to establish the underlying mechanism(s) accounting for the apoptotic-like death of Leishmania promastigotes by artemisinin, an endoperoxide. The formation of reactive oxygen species was confirmed by flow cytometry and was accompanied by inhibition of mitochondrial complexes I-III and II-III. However, this did not translate into a generation of mitochondrial superoxide or decrease in oxygen consumption, indicating minimal impairment of the electron transport chain. Artemisinin caused depolarization of the mitochondrial membrane along with a substantial depletion of adenosine triphosphatase (ATP), but it was not accompanied by enhancement of ATP hydrolysis. Collectively, the endoperoxide-mediated radical formation by artemisinin in Leishmania promastigotes was the key step for triggering its antileishmanial activity, leading secondarily to mitochondrial dysfunction indicating that endoperoxides represent a promising therapeutic strategy against Leishmania worthy of pharmacological consideration.

Treatment outcomes of visceral leishmaniasis in Ethiopia from 2001 to 2017: a systematic review and meta-analysis

Background

Ethiopia has the highest number of visceral leishmaniasis (VL) cases after Sudan in Sub-Saharan Africa. However, there was lack of comprehensive data on VL treatment outcome despite the huge burden of the diseases in the country. Hence, we aimed to perform a systematic review and meta-analysis on this topic to obtain stronger evidence on treatment outcomes of VL from the existing literature in Ethiopia.

Methods

The Cochrane guidelines to conduct meta-analysis following the Preferred Reporting Items for Systematic review and Meta-Analysis statement was used to conduct a computerized systematic search of the PubMed, Google Scholar, and ScienceDirect databases. Random effects model was used to combine studies showing heterogeneity of Cochrane Q P < 0.10 and I² > 50. Treatment outcomes were assessed at end of treatment and at 6 months follow-up. Subgroup analyses were performed on treatment outcomes based on the different antileishmanial treatment options and patients’ HIV status.

Results

Fifteen studies were included in the final analyses. At end of treatment, an overall treatment success rate of 82.6% was noticed. At 6 months follow-up, the overall treatment success rate was 72.2%. For patients treated with sodium stibogluconate (SSG), the treatment success rates at the end of treatment and at six-month follow-up were 81.5% and 80.7%, respectively. Multiple doses of liposomal-amphotericin B (L-AMB) had treatment success rates of 96.7 and 71–100% at the end of treatment and at 6 months follow-up, respectively. The combination of SSG with paromomycin (PM) gave treatment success rates of up to 90.1% at the end of treatment. HIV-infected individuals were found to have a higher mortality (odds ratio = 4.77, 95% CI: 1.30–17.43, P = 0.009) rate at 6 months follow-up.

Conclusions

SSG alone has shown lower treatment efficacy in the management of VL when compared to combination of SSG with PM and multiple doses of L-AMB. The combination of SSG with PM gave good treatment success rates with shorter duration of treatment. Hence, the combination of SSG with PM should be used preferentially over SSG monotherapy. Multiple doses of L-AMB showed great efficacy especially among patients with complications, severe disease, HIV co-infection, and intolerance to the adverse effects of antimonials. HIV-infected individuals had a worse prognosis than their HIV-negative counterparts.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0491-7) contains supplementary material, which is available to authorized users.