Imipramine exploits histone deacetylase 11 to increase the IL-12/IL-10 ratio in macrophages infected with antimony-resistant Leishmania donovani and clears organ parasites in experimental infection

Resolving the polycistronic aftermath: Essential role of topoisomerase IA in preventing R-loops in Leishmania

Kinetoplastid parasites are "living bridges" in the evolution from prokaryotes to higher eukaryotes. The near-intronless genome of the kinetoplastid Leishmania exhibits polycistronic transcription which can facilitate R-loop formation. Therefore, to prevent such DNA-RNA hybrids, Leishmania has retained prokaryotic-like DNA Topoisomerase IA (LdTOPIA) in the course of evolution. LdTOPIA is an essential enzyme that is expressed ubiquitously and is adapted for the compartmentalized eukaryotic form in harboring functional bipartite nuclear localization signals. Although exhibiting greater homology to mycobacterial TOPIA, LdTOPIA could functionally complement the growth lethality of Escherichia coli TOPIA null GyrB ts strain at non-permissive temperatures. Purified LdTOPIA exhibits Mg2+-dependent relaxation of only negatively supercoiled DNA and preference towards single-stranded DNA substrates. LdTOPIA prevents nuclear R-loops as conditional LdTOPIA downregulated parasites exhibit R-loop formation and thereby parasite killing. The clinically used tricyclic antidepressant, norclomipramine could specifically inhibit LdTOPIA and lead to R-loop formation and parasite elimination. This comprehensive study therefore paves an avenue for drug repurposing against Leishmania.

Single-cell ATAC sequencing identifies sleepy macrophages during reciprocity of cytokines in L. major infection

The hallmark characteristic of macrophages lies in their inherent plasticity, allowing them to adapt to dynamic microenvironments. Leishmania strategically modulates the phenotypic plasticity of macrophages, creating a favorable environment for intracellular survival and persistent infection through regulatory cytokine such as interleukin (IL)-10. Nevertheless, these effector cells can counteract infection by modulating crucial cytokines like IL-12 and key components involved in its production. Using sophisticated tool of single-cell assay for transposase accessible chromatin (ATAC) sequencing, we systematically examined the regulatory axis of IL-10 and IL-12 in a time-dependent manner during Leishmania major infection in macrophages Our analysis revealed the cellular heterogeneity post-infection with the regulators of IL-10 and IL-12, unveiling a reciprocal relationship between these cytokines. Notably, our significant findings highlighted the presence of sleepy macrophages and their pivotal role in mediating reciprocity between IL-10 and IL-12. To summarize, the roles of cytokine expression, transcription factors, cell cycle, and epigenetics of host cell machinery were vital in identification of sleepy macrophages, which is a transient state where transcription factors controlled the epigenetic remodeling and expression of genes involved in pro-inflammatory cytokine expression and recruitment of immune cells.IMPORTANCELeishmaniasis is an endemic affecting 99 countries and territories globally, as outlined in the 2022 World Health Organization report. The disease's severity is compounded by compromised host immune systems, emphasizing the pivotal role of the interplay between parasite and host immune factors in disease regulation. In instances of cutaneous leishmaniasis induced by L. major, macrophages function as sentinel cells. Our findings indicate that the plasticity and phenotype of macrophages can be modulated to express a cytokine profile involving IL-10 and IL-12, mediated by the regulation of transcription factors and their target genes post-L. major infection in macrophages. Employing sophisticated methodologies such as single-cell ATAC sequencing and computational genomics, we have identified a distinctive subset of macrophages termed "sleepy macrophages." These macrophages exhibit downregulated housekeeping genes while expressing a unique set of variable features. This data set constitutes a valuable resource for comprehending the intricate host-parasite interplay during L. major infection.

HDAC11 Regulates Palmitate-induced NLRP3 Inflammasome Activation by Inducing YAP Expression in THP-1 Cells and PBMCs

Histone deacetylase 11 (HDAC11) has been implicated in the pathogenesis of metabolic diseases characterized by chronic low-grade inflammation, such as obesity. However, the influence of HDAC11 on inflammation and the specific effect of HDAC11 on the palmitic acid (PA)-induced NLR family pyrin domain containing 3 (NLRP3) inflammasome activation are poorly understood. The effect of PA treatment on HDAC11 activity and the NLRP3 inflammasome was investigated in human peripheral blood mononuclear cells and THP-1 cells. The PA-induced responses of key markers of NLRP3 inflammasome activation, including NLRP3 gene expression, caspase-1 p10 activation, cleaved IL-1β production, and extracellular IL-1β release, were assessed as well. The role of HDAC11 was explored using a specific inhibitor of HDAC11 and by knockdown using small interfering (si)HDAC11 RNA. The relationship between HDAC11 and yes-associated protein (YAP) in the PA-induced NLRP3 inflammasome was investigated in THP-1 cells with HDAC11 or YAP knockdown. Following PA treatment, HDAC11 activity and protein levels increased significantly, concomitant with activation of the NLRP3 inflammasome. Notably, PA-induced the upregulation of NLRP3, caspase-1 p10 activation, the production of cleaved IL-1β, and the release of IL-1β into the extracellular space, all of which were attenuated by FT895 treatment and by HDAC11 knockdown. In THP-1 cells, PA induced the expression of YAP and its interaction with NLRP3, resulting in NLRP3 inflammasome activation, whereas both were inhibited by FT895 and siHDAC11 RNA. These findings demonstrate a pivotal role for HDAC11 in the PA-induced activation of the NLRP3 inflammasome. HDAC11 inhibition thus represents a promising therapeutic strategy for mitigating NLRP3 inflammasome-related inflammation in the context of obesity.

Largemouth bass Rel exerts antiviral role against fish virus and regulates the expression of interleukin-10

Nuclear factor-κB (NF-κB)/Rel is a group of transcription factors that can be activated and regulates various aspects of innate and adaptive immune functions, which play a crucial role in mediating inflammatory responses. Interleukin-10 (IL-10) is a highly pleiotropic cytokine that has a central role in limiting the immune response to pathogens during infection and thereby alleviating damage to the host. This study aims to investigate the function of the Rel gene in virus infection and its regulatory effect on IL-10 in the largemouth bass (Micropterus salmoides). The ORF sequence of MsRel was 1941 bp, containing 646 amino acids with two conserved functional domains, including RHD and IPT domain. In healthy largemouth bass, the mRNA of MsRel was detected in all the tested tissues, including gill, liver, kidney, heart, spleen, intestine, stomach, skin, brain, fin and muscle. The expression of MsRel was induced by challenge with largemouth bass virus (LMBV) or red grouper nervous necrosis virus (RGNNV), as well as treatment with lipopolysaccharide (LPS) or poly (I:C) in vivo. As evidenced by the detection of viral gene mRNA levels, the infectivity of LMBV and morphological cytopathic effect (CPE), we found that overexpression of MsRel inhibited the infection and replication of LMBV, suggesting its antiviral roles in fish. Besides, the promoter analysis was carried out to determine whether MsRel was a regulator of MsIL-10. The results of the luciferase reporter assay indicated that MsRel has a positive regulatory role in MsIL-10 expression. Further analysis revealed that the potential binding sites of MsIL-10 may be located in the MsIL10-5-M (-42 to +8 bp) region of the MsIL-10 promoter. Furthermore, we observed that MsRel enhanced IFN-I and IFN-III promoter activities. Taken together, our findings demonstrated that MsRel affect LMBV infection by regulating the immune responses, and providing a new idea of the mechanisms how Rel regulate the expression of IL-10 in bony fish.

Imipramine Administration in Brucella abortus 2308-Infected Mice Restores Hippocampal Serotonin Levels, Muscle Strength, and Mood, and Decreases Spleen CFU Count

Brucellosis infection causes non-specific symptoms such as fever, chills, sweating, headaches, myalgia, arthralgia, anorexia, fatigue, and mood disorders. In mouse models, it has been associated with increased levels of IL-6, TNF-α, and IFN-γ, a decrease in serotonin and dopamine levels within the hippocampus, induced loss of muscle strength and equilibrium, and increased anxiety and hopelessness. Imipramine (ImiP), a tricyclic antidepressant, is used to alleviate neuropathic pain. This study evaluated the effects of ImiP on Balb/c mice infected with Brucella abortus 2308 (Ba) at 14- and 28-days post-infection. Serum levels of six cytokines (IFN-γ, IL-6, TNF-α, IL-12, MCP-1. and IL-10) were assessed by FACS, while the number of bacteria in the spleen was measured via CFU. Serotonin levels in the hippocampus were analyzed via HPLC, and behavioral tests were conducted to assess strength, equilibrium, and mood. Our results showed that mice infected with Brucella abortus 2308 and treated with ImiP for six days (Im6Ba14) had significantly different outcomes compared to infected mice (Ba14) at day 14 post-infection. The mood was enhanced in the forced swimming test (FST) (p < 0.01), tail suspension test (TST) (p < 0.0001), and open-field test (p < 0.0001). Additionally, there was an increase in serotonin levels in the hippocampus (p < 0.001). Furthermore, there was an improvement in equilibrium (p < 0.0001) and muscle strength (p < 0.01). Lastly, there was a decrease in IL-6 levels (p < 0.05) and CFU count in the spleen (p < 0.0001). At 28 days, infected mice that received ImiP for 20 days (Im20Ba28) showed preservation of positive effects compared to infected mice (Ba28). These effects include the following: (1) improved FST (p < 0.0001) and TST (p < 0.0001); (2) better equilibrium (p < 0.0001) and muscle strength (p < 0.0001); (3) decreased IL-6 levels (p < 0.05); and (4) reduced CFU count in the spleen (p < 0.0001). These findings suggest the potential for ImiP to be used as an adjuvant treatment for the symptoms of brucellosis, which requires future studies.

Critical Functions of Histone Deacetylases (HDACs) in Modulating Inflammation Associated with Cardiovascular Diseases

Histone deacetylases (HDACs) are a superfamily of enzymes that catalyze the removal of acetyl functional groups from lysine residues of histone and non-histone proteins. There are 18 mammalian HDACs, which are classified into four classes based on the primary homology with yeast HDACs. Among these groups, Class I and II HDACs play a major role in lysine deacetylation of the N-terminal histone tails. In mammals, HDACs play a pivotal role in the regulation of gene transcription, cell growth, survival, and proliferation. HDACs regulate the expression of inflammatory genes, as evidenced by the potent anti-inflammatory activity of pan-HDAC inhibitors, which were implicated in several pathophysiologic states in the inflammation process. However, it is unclear how each of the 18 HDAC proteins specifically contributes to the inflammatory gene expression. It is firmly established that inflammation and its inability to converge are central mechanisms in the pathogenesis of several cardiovascular diseases (CVDs). Emerging evidence supports the hypothesis that several different pro-inflammatory cytokines regulated by HDACs are associated with various CVDs. Based on this hypothesis, the potential for the treatment of CVDs with HDAC inhibitors has recently begun to attract attention. In this review, we will briefly discuss (1) pathophysiology of inflammation in cardiovascular disease, (2) the function of HDACs in the regulation of atherosclerosis and cardiovascular diseases, and (3) the possible therapeutic implications of HDAC inhibitors in cardiovascular diseases. Recent studies reveal that histone deacetylase contributes critically to mediating the pathophysiology of inflammation in cardiovascular disease. HDACs are also recognized as one of the major mechanisms in the regulation of inflammation and cardiovascular function. HDACs show promise in developing potential therapeutic implications of HDAC inhibitors in cardiovascular and inflammatory diseases.

Activation of TLR-pathway to induce host Th1 immune respons eagainst visceral leishmaniasis: Involvement of galactosylated-flavonoids

Immunotherapeutic strategies against visceral leishmaniasis (VL) are pertinent because of the emergence of resistance against existing chemotherapy, coupled with their toxicity and high costs. Various bioactive components with potential immunomodulatory activity, such as alkaloids, terpenes, saponins, flavonoids obtained primarily from medicinal plants, have been screened against different disease models. Reports suggested that glycans containing terminal β-galactose can skew host immune response towards Th1 by engaging TLRs. In this study, two synthesized terminal galactose-containing flavones, Quercetin 3-d-galactoside (Q-gal) and Kaempferol 3-O-d-galactoside (K-gal), are profiled in terms of inducing host protective Th1 response in both in vitro & in vivo animal models of experimental VL individually against antimony-resistant & antimony-susceptible Leishmania donovani. Further, we explored that both Q-gal and K-gal induce TLR4 mediated Th1 response to encounter VL. Molecular docking analysis also suggested strong interaction with TLR4 for both the galactosides, with a slightly better binding potential towards Q-gal. Treatment with both Q-gal and K-gal showed significant antileishmanial efficacy. Each considerably diminished the liver and splenic parasite burden 60 days after post-infection (>90% in AG83 infected mice and >87% in GE1F8R infected mice) when administered at a 5 mg/kg/day body-weight dose for ten consecutive days. However, the treatments failed to clear the parasites in the TLR4 deficient C3H/HeJ mice. Treatment with these compounds favors the elevation of TLR4 dependent host protective Th1 cytokines and suppression of disease-promoting IL-10. Q-gal and K-gal also triggered sufficient ROS generation in macrophages to kill intracellular parasites directly.

•

Galactosilated flavonoids treatment clears in-vivo drug-resistant Leishmania donovani infection.

•

Quercetin 3-d-galactoside (Q-gal) & Kaempferol 3-O-d-galactoside (K-gal) induce host TLR4 pathway.

•

These flavonoids up-regulate Th1 cytokines and suppress the disease-promoting IL-10.

•

TLR4 deficient C3H/HeJ mice are unresponsive towards Q-gal and K-gal treatment.

Deletion of ACLY Disrupts Histone Acetylation and IL-10 Secretion in Trophoblasts, Which Inhibits M2 Polarization of Macrophages: A Possible Role in Recurrent Spontaneous Abortion

Changes to macrophage polarization affect the local microenvironment of the placenta, resulting in pathological pregnancy diseases such as recurrent spontaneous abortion (RSA). Macrophages are in close contact with trophoblasts during placental development, and trophoblast-derived cytokines are important regulators of macrophage polarization and function. Histone acetylation can affect the expression and secretion of cytokines, and ATP citrate lyase (ACLY) is an important factor that regulates histone acetylation. The aim of this study was to investigate the effect of ACLY expression differences in trophoblast on macrophage polarization and its mechanism. Our data demonstrate that ACLY level in placental villi of patients with RSA is decreased, which may lead to the inhibition of histone acetylation in trophoblasts, thereby reducing the secretion of IL-10. Reduced IL-10 secretion activates endoplasmic reticulum stress in macrophages, thus inhibiting their M2 polarization.

Host-directed antileishmanial interventions: Harvesting unripe fruits to reach fruition

Leishmaniasis is an exemplary paradigm of immune evasion, fraught with the perils of limited clinical assistance, escalating costs of treatment and made worse with the lack of suitable vaccine. While drugs remain central to large-scale disease control, the growing emergence of parasite resistance necessitates the need for combination therapy involving host-directed immunological agents. Also, since prolonged disease progression is associated with strong immune suppression of the host, augmentation of host immunity via restoration of the immunoregulatory circuit involving antigen-presenting cells and T-cells, activation of macrophage function and/or CD4⁺ T helper 1 cell differentiation may serve as an ideal approach to resolve severe cases of leishmaniasis. As such, therapies that embody a synergistic approach that involve direct killing of the parasite in addition to elevating host immunity are likely to pave the way for widespread elimination of leishmaniasis in the future. With this review, we aim to recapitulate the various immunotherapeutic agents found to hold promise in antileishmanial treatment both in vitro and in vivo. These include parasite-specific antigens, dendritic cell-targeted therapy, recombinant inhibitors of various components intrinsic to immune cell signaling and agonists or antagonists to immune cells and cytokines. We also summarize their abilities to direct therapeutic skewing of the host cell-immune response and review their potential to combat the disease either alone, or as adjunct modalities.

Going ballistic: Leishmania nuclear subversion of host cell plasticity

Intracellular parasites have evolved intricate strategies to subvert host cell functions for their own survival. These strategies are particularly damaging to the host if the infection involves immune cells, as illustrated by protozoan parasites of the genus Leishmania that thrive inside mononuclear phagocytic cells, causing devastating immunopathologies. While the impact of Leishmania infection on host cell phenotype and functions has been well documented, the regulatory mechanisms underlying host cell subversion were only recently investigated. Here we summarize the current knowledge on how Leishmania infection affects host nuclear activities and propose thought-provoking new concepts on the reciprocal relationship between epigenetic and transcriptional regulation in host cell phenotypic plasticity, its potential subversion by the intracellular parasite, and its relevance for host-directed therapy.

Highlighting the interplay of microRNAs from Leishmania parasites and infected-host cells

Leishmania parasites, the causative agents of leishmaniasis, are protozoan parasites with the ability to modify the signalling pathway and cell responses of their infected host cells. These parasite strategies alter the host cell environment and conditions favouring their replication, survival and pathogenesis. Since microRNAs (miRNAs) are able to post-transcriptionally regulate gene expression processes, these biomolecules can exert critical roles in controlling Leishmania-host cell interplay. Therefore, the identification of relevant miRNAs differentially expressed in Leishmania parasites as well as in infected cells, which affect the host fitness, could be critical to understand the infection biology, pathogenicity and immune response against these parasites. Accordingly, the current review aims to address the differentially expressed miRNAs in both, the parasite and infected host cells and how these biomolecules change cell signalling and host immune responses during infection. A deep understanding of these processes could provide novel guidelines and therapeutic strategies for managing and treating leishmaniasis.

Preclinical and clinical progress for HDAC as a putative target for epigenetic remodeling and functionality of immune cells

Genetic changes are difficult to reverse; thus, epigenetic aberrations, including changes in DNA methylation, histone modifications, and noncoding RNAs, with potential reversibility, have attracted attention as pharmaceutical targets. The current paradigm is that histone deacetylases (HDACs) regulate gene expression via deacetylation of histone and nonhistone proteins or by forming corepressor complexes with transcription factors. The emergence of epigenetic tools related to HDACs can be used as diagnostic and therapeutic markers. HDAC inhibitors that block specific or a series of HDACs have proven to be a powerful therapeutic treatment for immune-related diseases. Here, we summarize the various roles of HDACs and HDAC inhibitors in the development and function of innate and adaptive immune cells and their implications for various diseases and therapies.

Modulation of Splenic B Cell Subsets during Experimental Leishmania donovani Infection in BALB/c Mice

Sodium antimonials are one of the major and common drugs used against visceral form leishmaniasis (VL). However, the development of drug resistance makes it difficult to manage this disease. Current work investigates the modulation of splenic B cells during experimental infection with antimony-sensitive and -resistant Leishmania donovani infection. Here we phenotypically characterized splenic B cell subsets in BALB/c mice infected with antimony drug-sensitive and -resistant VL strains using flow-cytometry method. In the splenocytes we noticed increased number of Transitional T3 B cells and B1a B cells in drug-resistant VL strain infection. Besides, we also observed alteration in Follicular B cell population of antimony-resistant strain infected mice. Drug-resistant strain induced secretion of elevated level of IL-10 from B1a B cells and IL-6 from Transitional T3 B cell subsets in the splenocytes. Purified splenic B cells from antimony drug-resistant strain infected mice showed decrease in the Lyn kinase gene expression compared to sensitive strain infected and uninfected mice. The current study provides insight into changes in host splenic B-cell subsets during experimental infection with antimony-sensitive and -resistant L. donovani in murine model.

Short-Course Treatment With Imipramine Entrapped in Squalene Liposomes Results in Sterile Cure of Experimental Visceral Leishmaniasis Induced by Antimony Resistant Leishmania donovani With Increased Efficacy

Previously we have shown that long term oral treatment of tricyclic-antidepressant-drug, imipramine, against experimental visceral leishmaniasis, results in clearance of organ parasites, regardless of input infection, either with antimony-sensitive (Sb^S) or antimony-resistant (Sb^R) Leishmania donovani (LD) clinical isolates. Although continuous imipramine monotherapy for 28 days (5 mg/kg) results in significant clearance of organ parasites in both Sb^R and Sb^SLD infected hamsters, the dose for the sterile parasite clearance from visceral organ is comparatively higher (10 mg/kg) and shows signs of toxicity. Hence, to reduce the toxicity, we encapsulated imipramine in squalene-phosphatidylcholine (SP) liposome (Lip-Imi) and tested its efficacy for a short-course treatment (10 days) in the animal model of visceral leishmaniasis. We observed a significant reduction of hepatic toxicity coupled with sterile parasite clearance in case of this short-course treatment of Lip-Imi, which is absent with free Imi treatment. This also correlates with significant increase in serum availability of imipramine in case of Lip-Imi treatment due to sustained release. Clearance of parasite was coupled with the polarization of antileishmanial immune repertoire from Th2 to Th1 after treatment with Lip-Imi in both Sb^RLD and Sb^SLD infected mouse models of LD infection. This study showed that imipramine is effective against both Sb^SLD and Sb^RLD at a significantly lower dose with reduced time course of treatment without any toxic side effects, when encapsulated in SP-liposome. Thus, the drug has the potential to be repurposed for the treatment of Kala-azar.

Probing the molecular mechanism of aggressive infection by antimony resistant Leishmania donovani

The disease visceral leishmaniasis (VL) or kala azar is caused by the protozoan parasite, Leishmania donovani (LD). For many decades the pentavalent antimonial drugs countered the successive epidemics of the disease in the Indian sub-continent and elsewhere. With time, antimony resistant LD (LD^R) developed and the drug in turn lost its efficacy. Infection of mammals with LD^R gives rise to aggressive infection as compared to its sensitive counterpart (LD^S) coupled with higher surge of IL-10 and TGF-β. The IL-10 causes upregulation of multidrug resistant protein-1 which causes efflux of antimonials from LD^R infected cells. This is believed to be a key mechanism of antimony resistance. MicroRNAs (miRNAs) are tiny post-transcriptional regulators of gene expression in mammalian cells and in macrophage play a pivotal role in controlling the expression of cytokines involved in infection process. Therefore, a change in miRNA profiles of macrophages infected with LD^S or LD^R could explain the differential cytokine response observed. Interestingly, the outcome of LD infection is also governed by the critical balance of pro- and anti-inflammatory cytokines which is inturn regulated by miRNA-Ago2 or miRNP complex and its antagonist RNA binding protein HuR. Here Ago2 plays the fulcrum whose phosphorylation and de-phosphorylation dictates the process; which in turn is controlled by PP2A and HuR. LD^S and LD^R upregulate PP2A and downregulate HuR at different magnitude leading to various levels of anti-inflammatory to proinflammatory cytokine production and resulting pathology in the host. While ectopic HuR expression alone is sufficient to clear LD^S infection, simultaneous upregulation of HuR and inhibition of PP2A is required to inhibit LD^R mediated infection. Therefore, tampering with miRNA pathway could be a new strategy to control infection caused by LD^R parasite.

Epigenetic Changes Associated With Interleukin-10

IL-10 is a regulator of inflammation and immunosuppression. IL-10 regulates a variety of immune cells to limit and stop the inflammatory response, and thus plays an important role in autoimmune diseases, inflammatory diseases and cancer. IL-10 is closely related to epigenetic modification, in which changes in DNA methylation of IL-10 gene can affect mRNA and protein levels of IL-10. In addition, changes in histone modifications, especially histone acetylation, can also lead to abnormal expression of IL-10 mRNA. At the same time, a handful of IL-10 related microRNAs (miRNAs) are found to be aberrantly expressed in multiple diseases. Besides, long non-coding RNA (lncRNA) growth arrest specific transcript 5 (GAS5) also inhibits IL-10 expression. Here, we reviewed the epigenetic changes related to IL-10 in various diseases, as well as the regulation of IL-10 gene expression in various diseases by epigenetic modifications such as DNA methylation, histone modification, miRNA, and lncRNA.

Functional Inhibition of Host Histone Deacetylases (HDACs) Enhances in vitro and in vivo Anti-mycobacterial Activity in Human Macrophages and in Zebrafish

The rapid and persistent increase of drug-resistant Mycobacterium tuberculosis (Mtb) infections poses increasing global problems in combatting tuberculosis (TB), prompting for the development of alternative strategies including host-directed therapy (HDT). Since Mtb is an intracellular pathogen with a remarkable ability to manipulate host intracellular signaling pathways to escape from host defense, pharmacological reprogramming of the immune system represents a novel, potentially powerful therapeutic strategy that should be effective also against drug-resistant Mtb. Here, we found that host-pathogen interactions in Mtb-infected primary human macrophages affected host epigenetic features by modifying histone deacetylase (HDAC) transcriptomic levels. In addition, broad spectrum inhibition of HDACs enhanced the antimicrobial response of both pro-inflammatory macrophages (Mϕ1) and anti-inflammatory macrophages (Mϕ2), while selective inhibition of class IIa HDACs mainly decreased bacterial outgrowth in Mϕ2. Moreover, chemical inhibition of HDAC activity during differentiation polarized macrophages into a more bactericidal phenotype with a concomitant decrease in the secretion levels of inflammatory cytokines. Importantly, in vivo chemical inhibition of HDAC activity in Mycobacterium marinum-infected zebrafish embryos, a well-characterized animal model for tuberculosis, significantly reduced mycobacterial burden, validating our in vitro findings in primary human macrophages. Collectively, these data identify HDACs as druggable host targets for HDT against intracellular Mtb.

Searching for drugs for Chagas disease, leishmaniasis and schistosomiasis: a review

Chagas disease, leishmaniasis and schistosomiasis are neglected diseases (NDs) and are a considerable global challenge. Despite the huge number of people infected, NDs do not create interest from pharmaceutical companies because the associated revenue is generally low. Most of the research on these diseases has been conducted in academic institutions. The chemotherapeutic armamentarium for NDs is scarce and inefficient and better drugs are needed. Researchers have found some promising potential drug candidates using medicinal chemistry and computational approaches. Most of these compounds are synthetic but some are from natural sources or are semi-synthetic. Drug repurposing or repositioning has also been greatly stimulated for NDs. This review considers some potential drug candidates and provides details of their design, discovery and activity.

Protective or Detrimental? Understanding the Role of Host Immunity in Leishmaniasis

The intracellular protozoan parasites of the genus Leishmania are the causative agents of leishmaniasis, a vector-borne disease of major public health concern, estimated to affect 12 million people worldwide. The clinical manifestations of leishmaniasis are highly variable and can range from self-healing localized cutaneous lesions to life-threatening disseminated visceral disease. Once introduced into the skin by infected sandflies, Leishmania parasites interact with a variety of immune cells, such as neutrophils, monocytes, dendritic cells (DCs), and macrophages. The resolution of infection requires a finely tuned interplay between innate and adaptive immune cells, culminating with the activation of microbicidal functions and parasite clearance within host cells. However, several factors derived from the host, insect vector, and Leishmania spp., including the presence of a double-stranded RNA virus (LRV), can modulate the host immunity and influence the disease outcome. In this review, we discuss the immune mechanisms underlying the main forms of leishmaniasis, some of the factors involved with the establishment of infection and disease severity, and potential approaches for vaccine and drug development focused on host immunity.

Sertraline Delivered in Phosphatidylserine Liposomes Is Effective in an Experimental Model of Visceral Leishmaniasis

Liposomes containing phosphatidylserine (PS) has been used for the delivery of drugs into the intramacrophage milieu. Leishmania (L.) infantum parasites live inside macrophages and cause a fatal and neglected viscerotropic disease, with a toxic treatment. Sertraline was studied as a free formulation (SERT) and also entrapped into phosphatidylserine liposomes (LP-SERT) against intracellular amastigotes and in a murine model of visceral leishmaniasis. LP-SERT showed a potent activity against intracellular amastigotes with an EC₅₀ value of 2.5 μM. The in vivo efficacy of SERT demonstrated a therapeutic failure. However, when entrapped into negatively charged liposomes (−58 mV) of 125 nm, it significantly reduced the parasite burden in the mice liver by 89% at 1 mg/kg, reducing the serum levels of the cytokine IL-6 and upregulating the levels of the chemokine MCP-1. Histopathological studies demonstrated the presence of an inflammatory infiltrate with the development of granulomas in the liver, suggesting the resolution of the infection in the treated group. Delivery studies showed fluorescent-labeled LP-SERT in the liver and spleen of mice even after 48 h of administration. This study demonstrates the efficacy of PS liposomes containing sertraline in experimental VL. Considering the urgent need for VL treatments, the repurposing approach of SERT could be a promising alternative.

Leishmania-Host Interactions-An Epigenetic Paradigm

Leishmaniasis is one of the major neglected tropical diseases, for which no vaccines exist. Chemotherapy is hampered by limited efficacy coupled with development of resistance and other side effects. Leishmania parasites elude the host defensive mechanisms by modulating their surface proteins as well as dampening the host's immune responses. The parasites use the conventional RNA polymerases peculiarly under different environmental cues or pressures such as the host's milieu or the drugs. The mechanisms that restructure post-translational modifications are poorly understood but altered epigenetic histone modifications are believed to be instrumental in influencing the chromatin remodeling in the parasite. Interestingly, the parasite also modulates gene expression of the hosts, thereby hijacking or dampening the host immune response. Epigenetic factor such as DNA methylation of cytosine residues has been incriminated in silencing of macrophage-specific genes responsible for defense against these parasites. Although there is dearth of information regarding the epigenetic alterations-mediated pathogenesis in these parasites and the host, the unique epigenetic marks may represent targets for potential anti-leishmanial drug candidates. This review circumscribes the epigenetic changes during Leishmania infection, and the epigenetic modifications they enforce upon the host cells to ensure a safe haven. The non-coding micro RNAs as post-transcriptional regulators and correlates of wound healing and toll-like receptor signaling, as well as prognostic biomarkers of therapeutic failure and healing time are also explored. Finally, we highlight the recent advances on how the epigenetic perturbations may impact leishmaniasis vaccine development as biomarkers of safety and immunogenicity.

HDAC11 is a regulator of diverse immune functions

Histone deacetylases deacetylate histone and non-histone protein targets. Aberrant HDAC expression and function have been observed in several diseases, which make these enzymes attractive treatment targets. Here, we summarize recent literature that addresses the roles of HDAC11 on the regulation of different immune cells including neutrophils, myeloid derived suppressor cells and T-cells. HDAC11 was initially identified as a negative regulator of the well-known anti-inflammatory cytokine IL-10. Hence, antagonizing HDAC11 activity may have anti-tumor potential, whereas activating HDAC11 may be useful to treat chronic inflammation or autoimmunity. However, to anticipate biological side-effects of HDAC11 modulators, more molecular insights will be required.

Mahanine exerts in vitro and in vivo antileishmanial activity by modulation of redox homeostasis

Earlier we have established a carbazole alkaloid (mahanine) isolated from an Indian edible medicinal plant as an anticancer agent with minimal effect on normal cells. Here we report for the first time that mahanine-treated drug resistant and sensitive virulent Leishmania donovani promastigotes underwent apoptosis through phosphatidylserine externalization, DNA fragmentation and cell cycle arrest. An early induction of reactive oxygen species (ROS) suggests that the mahanine-induced apoptosis was mediated by oxidative stress. Additionally, mahanine-treated Leishmania-infected macrophages exhibited anti-amastigote activity by nitric oxide (NO)/ROS generation along with suppression of uncoupling protein 2 and Th1-biased cytokines response through modulating STAT pathway. Moreover, we have demonstrated the interaction of a few antioxidant enzymes present in parasite with mahanine through molecular modeling. Reduced genetic and protein level expression of one such enzyme namely ascorbate peroxidase was also observed in mahanine-treated promastigotes. Furthermore, oral administration of mahanine in acute murine model exhibited almost complete reduction of parasite burden, upregulation of NO/iNOS/ROS/IL-12 and T cell proliferation. Taken together, we have established a new function of mahanine as a potent antileishmanial molecule, capable of inducing ROS and exploit antioxidant enzymes in parasite along with modulation of host's immune response which could be developed as an inexpensive and nontoxic therapeutics either alone or in combination.

The enemy within: Targeting host-parasite interaction for antileishmanial drug discovery

The state of antileishmanial chemotherapy is strongly compromised by the emergence of drug-resistant Leishmania. The evolution of drug-resistant phenotypes has been linked to the parasites’ intrinsic genome instability, with frequent gene and chromosome amplifications causing fitness gains that are directly selected by environmental factors, including the presence of antileishmanial drugs. Thus, even though the unique eukaryotic biology of Leishmania and its dependence on parasite-specific virulence factors provide valid opportunities for chemotherapeutical intervention, all strategies that target the parasite in a direct fashion are likely prone to select for resistance. Here, we review the current state of antileishmanial chemotherapy and discuss the limitations of ongoing drug discovery efforts. We finally propose new strategies that target Leishmania viability indirectly via mechanisms of host–parasite interaction, including parasite-released ectokinases and host epigenetic regulation, which modulate host cell signaling and transcriptional regulation, respectively, to establish permissive conditions for intracellular Leishmania survival.

The leishmanicidal activity of oleuropein is selectively regulated through inflammation- and oxidative stress-related genes

Background

Much research effort has been focused on investigating new compounds derived from low-cost sources, such as natural products, for treating leishmaniasis. Oleuropein derived from numerous plants, particularly from the olive tree, Olea europaea L. (Oleaceae), is a biophenol with many biological activities. Our previous findings showed that oleuropein exhibits leishmanicidal effects against three Leishmania spp. in vitro, and minimizes the parasite burden in L. donovani-infected BALB/c mice. The aim of the present study is to investigate the possible mechanism(s) that mediate this leishmanicidal activity.

Methods

We determined the efficacy of oleuropein in elevating ROS and NO production in L. donovani-infected J774A.1 macrophages and in explanted splenocytes and hepatocytes obtained from L. donovani-infected BALB/c mice. We also assessed the expression of genes that are related to inflammation, T-cell polarization and antioxidant defense, in splenocytes. Finally, we determined the ratios of specific IgG2a/IgG1 antibodies and DTH reactions in L. donovani-infected BALB/c mice treated with oleuropein.

Results

Oleuropein was able to elevate ROS production in both in vitro and in vivo models of visceral leishmaniasis and raised NO production in ex vivo cultures of splenocytes and hepatocytes. The extensive oxidative stress found in oleuropein-treated mice was obviated by the upregulation of the host’s antioxidant enzyme (mGCLC) and the simultaneous downregulation of the corresponding enzyme of the parasite (LdGCLC). Moreover, oleuropein was able to mount a significant Th1 polarization characterized by the expression of immune genes (IL-12β, IL-10, TGF-β1, IFN-γ) and transcription factors (Tbx21 and GATA3). Moreover, this immunomodulatory effect was also correlated with an inhibitory effect on IL-1β gene expression, rather than with the expression of IL-1α, IL-1rn and TNF-α. Furthermore, oleuropein-treated BALB/c mice mounted a delayed-type hypersensitivity (DTH) response and an elevated Leishmania-specific IgG2a/IgG1 ratio that clearly demonstrated an in vivo protective mechanism.

Conclusion

The ability of Oleuropein to promote a Th1 type immune response in L. donovani-infected BALB/c mice points towards the candidacy of this bioactive compound as an immunomodulatory agent that may complement therapeutic approaches to leishmaniasis.

The role of macrophages in anti-inflammatory activity of antidepressant drugs

Depression is a common disease influencing patients' quality of life, whose etiology involves complex interactions of environmental, genetic and immunological factors. The latter factors include proinflammatory activation of monocytes and macrophages and increased serum levels of proinflammatory cytokines, altogether formulated as the "macrophage theory of depression". Our current review summarizes the impact of the most commonly used antidepressant drugs on the immune response with special emphasis on the role of macrophages in the clinically observed effects. The anti-inflammatory action of antidepressants mainly results from their direct interaction with immune cells and from changes in the concentration and the relations of neurotransmitters sensed by these cells. The summarized data revealed that Mφs are one of the leading cell populations involved in drug-mediated immune effects that can be observed both in subjects with depression as well as in individuals not suffering from depression. Thus, currently reviewed immunomodulatory effects of the experimental use of different antidepressant drugs suggest the possibility of utilizing them in complex therapeutic strategies dedicated to various inflammatory and immune-mediated diseases. It is worth noting that an excessive inflammatory reaction is also associated with the pathogenesis of various cardiovascular, metabolic and neuro-endocrine diseases. Thus, the inclusion of antidepressants in the complex therapy of these disorders may have beneficial effects through the enhancement of the mood of the patient and alleviation of chronic inflammation. On the other hand, presented data suggest that the influence of chronically used antidepressants on anti-microbial and anti-tumor immunity could also be taken into consideration.

Regulatory IgDhi B Cells Suppress T Cell Function via IL-10 and PD-L1 during Progressive Visceral Leishmaniasis

During visceral leishmaniasis (VL), Th1-based inflammation is induced to control intracellular parasites. Inflammation-based pathology was shown to be dampened by IL-10 and eventual programmed death 1-mediated T cell exhaustion. Cell type(s) responsible for the initiation of T cell-produced IL-10 during VL are unknown. CD19(+), CD5(-), CD1d(-), IgD(hi) regulatory B cells from healthy controls produced IL-10 in the absence of infection or stimulation, in contrast to IgD(lo/neg) B cells. IgD(hi) B cells may have a de novo versus induced regulatory program. The population of IgD(hi) B cells increased 3-fold as VL progressed. B cells from VL dogs were necessary and sufficient to suppress Th1 cell effector function. IgD(hi) B cells induced IL-10 production by T cells and IgD(lo) B cells. Blockage of B cell-specific PD-L1 restored Th1 responses. IgD(hi) regulatory B cells represent a novel regulatory B cell that may precipitate T cell exhaustion during VL.

Antimony-Resistant Leishmania donovani Exploits miR-466i To Deactivate Host MyD88 for Regulating IL-10/IL-12 Levels during Early Hours of Infection

Infection with antimony-resistant Leishmania donovani (Sb(R)LD) induces aggressive pathology in the mammalian hosts as compared with ones with antimony-sensitive L. donovani (Sb(S)LD) infection. Sb(R)LD, but not Sb(S)LD, interacts with TLR2/TLR6 to induce IL-10 by exploiting p50/c-Rel subunits of NF-κB in infected macrophages (Mϕs). Most of the TLRs exploit the universal adaptor protein MyD88 to activate NF-κB. We now show that infection of Mϕs from MyD88(-/-) mice with Sb(R)LD gave rise to significantly higher intracellular parasite number coupled with elevated IL-10/IL-12 ratio in the culture supernatant as compared with infection in wild type (WT) Mϕs. Τhese attributes were not seen with Sb(S)LD in similar experiments. Further, Sb(R)LD infection upregulated miR-466i, which binds with 3'-untranslated region, leading to the downregulation of MyD88. Infection of MyD88(-/-) Mϕ or IL-12(-/-) Mϕ with Sb(R)LD induced IL-10 surge at 4 h, whereas the same in WT Mϕ started from 12 h. Thus, absence of IL-12 in MyD88(-/-) mice favored early binding of NF-κB subunits to the IL-10 promoter, resulting in IL-10 surge. Infection of MyD88(-/-) mice with Sb(R)LD showed significantly higher organ parasites coupled with ill-defined and immature hepatic granulomas, whereas in WT mice there were less organ parasites and the granulomas were well defined. From the survival kinetics it was observed that Sb(R)LD-infected MyD88(-/-) mice died by 60 d postinfection, whereas the WT mice continued to survive. Our results demonstrate that Sb(R)LD has evolved a unique strategy to evade host antileishmanial immune repertoire by manipulating host MyD88 to its advantage.