Trypanosomatid Infections: How Do Parasites and Their Excreted-Secreted Factors Modulate the Inducible Metabolism of l-Arginine in Macrophages?

Traditional Chinese medicine in regulating macrophage polarization in immune response of inflammatory diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Numerous studies have demonstrated that various traditional Chinese medicines (TCMs) exhibit potent anti-inflammatory effects against inflammatory diseases mediated through macrophage polarization and metabolic reprogramming.

AIM OF THE STUDY

The objective of this review was to assess and consolidate the current understanding regarding the pathogenic mechanisms governing macrophage polarization in the context of regulating inflammatory diseases. We also summarize the mechanism action of various TCMs on the regulation of macrophage polarization, which may contribute to facilitate the development of natural anti-inflammatory drugs based on reshaping macrophage polarization.

MATERIALS AND METHODS

We conducted a comprehensive review of recently published articles, utilizing keywords such as "macrophage polarization" and "traditional Chinese medicines" in combination with "inflammation," as well as "macrophage polarization" and "inflammation" in conjunction with "natural products," and similar combinations, to search within PubMed and Google Scholar databases.

RESULTS

A total of 113 kinds of TCMs (including 62 components of TCMs, 27 TCMs as well as various types of extracts of TCMs and 24 Chinese prescriptions) was reported to exert anti-inflammatory effects through the regulation of key pathways of macrophage polarization and metabolic reprogramming.

CONCLUSIONS

In this review, we have analyzed studies concerning the involvement of macrophage polarization and metabolic reprogramming in inflammation therapy. TCMs has great advantages in regulating macrophage polarization in treating inflammatory diseases due to its multi-pathway and multi-target pharmacological action. This review may contribute to facilitate the development of natural anti-inflammatory drugs based on reshaping macrophage polarization.

Leishmaniasis: Immune Cells Crosstalk in Macrophage Polarization

Leishmaniasis is a complex infectious parasitic disease caused by protozoa of the genus Leishmania, belonging to a group of neglected tropical diseases. It establishes significant global health challenges, particularly in socio-economically disadvantaged regions. Macrophages, as innate immune cells, play a crucial role in initiating the inflammatory response against the pathogens responsible for this disease. Macrophage polarization, the process of differentiating macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, is essential for the immune response in leishmaniasis. The M1 phenotype is associated with resistance to Leishmania infection, while the M2 phenotype is predominant in susceptible environments. Notably, various immune cells, including T cells, play a significant role in modulating macrophage polarization by releasing cytokines that influence macrophage maturation and function. Furthermore, other immune cells can also impact macrophage polarization in a T-cell-independent manner. Therefore, this review comprehensively examines macrophage polarization's role in leishmaniasis and other immune cells' potential involvement in this intricate process.

Comparative transcriptomic analysis of the larval and adult stages of Dibothriocephalus dendriticus (Cestoda: Diphyllobothriidea)

Tapeworms of the genus Dibothriocephalus are widely distributed throughout the world, some of which are agents of human diphyllobothriasis, one of the most important fish-borne zoonoses caused by a cestode parasite. Genomic and transcriptomic data can be used to develop future diagnostic tools and epidemiological studies. The present work focuses on a comparative analysis of the transcriptomes of adult and plerocercoid D. dendriticus and the identification of their differentially expressed genes (DEGs). Transcriptome assembly and analysis yielded and annotated 35,129 unigenes, noting that 16,568 (47%) unigenes were not annotated in known databases, which may indicate a unique set of expressed transcripts for D. dendriticus. A total of 8022 differentially expressed transcripts were identified, including 3225 upregulated and 4797 downregulated differentially expressed transcripts from the plerocercoid and adult animals. The analysis of DEGs has shown that among the most differentially expressed genes, there are important genes characteristic of each stage. Thus, several genes are characteristic of D. dendriticus plerocercoids, including fatty acid-binding protein and ferritin. Among the most highly expressed DEGs of the adult stage of D. dendriticus is the Kunitz-type serine protease inhibitor, in two putative isoforms. The analyses of GO and KEGG metabolic pathways revealed that a large number of the DEGs of D. dendriticus are associated with the biosynthesis of various substances such as arginine and folate, as well as with various metabolic pathways such as galactose metabolism, selenocompound metabolism, and phosphonate and phosphinate metabolism. This will contribute to further research aimed at identifying targets for new generation drugs and the development of specific vaccines.

Induction of Autophagy by Ursolic Acid Promotes the Elimination of Trypanosoma cruzi Amastigotes From Macrophages and Cardiac Cells

Chagas disease, caused by the parasite Trypanosoma cruzi, is an infectious illness endemic to Latin America and still lacks an effective treatment for the chronic stage. In a previous study in our laboratory, we established the protective role of host autophagy in vivo during T. cruzi infection in mice and proposed this process as one of the mechanisms involved in the innate immune response against this parasite. In the search for an autophagy inducer that increases the anti-T. cruzi response in the host, we found ursolic acid (UA), a natural pentacyclic triterpene with many biological actions including autophagy induction. The aim of this work was to study the effect of UA on T. cruzi infection in vitro in the late infection stage, when the nests of intracellular parasites are forming, in both macrophages and cardiac cells. To test this effect, the cells were infected with T. cruzi for 24 h and then treated with UA (5–10 µM). The data showed that UA significantly decreased the number of amastigotes found in infected cells in comparison with non-treated cells. UA also induced the autophagy response in both macrophages and cardiac cells under the studied conditions, and the inhibition of this pathway during UA treatment restored the level of infection. Interestingly, LC3 protein, the main marker of autophagy, was recruited around amastigotes and the acidic probe LysoTracker localized with them, two key features of xenophagy. A direct cytotoxic effect of UA was also found on trypomastigotes of T. cruzi, whereas epimastigotes and amastigotes displayed more resistance to this drug at the studied concentrations. Taken together, these data showed that this natural compound reduces T. cruzi infection in the later stages by promoting parasite damage through the induction of autophagy. This action, in addition to the effect of this compound on trypomastigotes, points to UA as an interesting lead for Chagas disease treatment in the future.

Unique thiol metabolism in trypanosomatids: Redox homeostasis and drug resistance

Trypanosomatids are mainly responsible for heterogeneous parasitic diseases: Leishmaniasis, Sleeping sickness, and Chagas disease and control of these diseases implicates serious challenges due to the emergence of drug resistance. Redox-active biomolecules are the endogenous substances in organisms, which play important role in the regulation of redox homeostasis. The redox-active substances like glutathione, trypanothione, cysteine, cysteine persulfides, etc., and other inorganic intermediates (hydrogen peroxide, nitric oxide) are very useful as defence mechanism. In the present review, the suitability of trypanothione and other essential thiol molecules of trypanosomatids as drug targets are described in Leishmania and Trypanosoma. We have explored the role of tryparedoxin, tryparedoxin peroxidase, ascorbate peroxidase, superoxide dismutase, and glutaredoxins in the anti-oxidant mechanism and drug resistance. Up-regulation of some proteins in trypanothione metabolism helps the parasites in survival against drug pressure (sodium stibogluconate, Amphotericin B, etc.) and oxidative stress. These molecules accept electrons from the reduced trypanothione and donate their electrons to other proteins, and these proteins reduce toxic molecules, neutralize reactive oxygen, or nitrogen species; and help parasites to cope with oxidative stress. Thus, a better understanding of the role of these molecules in drug resistance and redox homeostasis will help to target metabolic pathway proteins to combat Leishmaniasis and trypanosomiases.

Panacea within a Pandora's box: the antiparasitic effects of phospholipases A2 (PLA2s) from snake venoms

Parasitic diseases affect millions of individuals worldwide, mainly in low-income regions. There is no cure for most of these diseases, and the treatment relies on drugs that have side effects and lead to drug resistance, emphasizing the urgency to find new treatments. Snake venom has been gaining prominence as a rich source of molecules with antiparasitic potentials, such as phospholipases A₂ (PLA₂s). Here, we compile the findings involving PLA₂s with antiparasitic activities against helminths, Plasmodium, Toxoplasma, and trypanosomatids. We indicate their molecular features, highlighting the possible antiparasitic mechanisms of action of these proteins. We also demonstrate interactions between PLA₂s and some parasite membrane components, shedding light on potential targets for drug design that may provide better treatment for the illnesses caused by parasites.

Trypanosomatid-Caused Conditions: State of the Art of Therapeutics and Potential Applications of Lipid-Based Nanocarriers

Trypanosomatid-caused conditions (African trypanosomiasis, Chagas disease, and leishmaniasis) are neglected tropical infectious diseases that mainly affect socioeconomically vulnerable populations. The available therapeutics display substantial limitations, among them limited efficacy, safety issues, drug resistance, and, in some cases, inconvenient routes of administration, which made the scenarios with insufficient health infrastructure settings inconvenient. Pharmaceutical nanocarriers may provide solutions to some of these obstacles, improving the efficacy-safety balance and tolerability to therapeutic interventions. Here, we overview the state of the art of therapeutics for trypanosomatid-caused diseases (including approved drugs and drugs undergoing clinical trials) and the literature on nanolipid pharmaceutical carriers encapsulating approved and non-approved drugs for these diseases. Numerous studies have focused on the obtention and preclinical assessment of lipid nanocarriers, particularly those addressing the two currently most challenging trypanosomatid-caused diseases, Chagas disease, and leishmaniasis. In general, in vitro and in vivo studies suggest that delivering the drugs using such type of nanocarriers could improve the efficacy-safety balance, diminishing cytotoxicity and organ toxicity, especially in leishmaniasis. This constitutes a very relevant outcome, as it opens the possibility to extended treatment regimens and improved compliance. Despite these advances, last-generation nanosystems, such as targeted nanocarriers and hybrid systems, have still not been extensively explored in the field of trypanosomatid-caused conditions and represent promising opportunities for future developments. The potential use of nanotechnology in extended, well-tolerated drug regimens is particularly interesting in the light of recent descriptions of quiescent/dormant stages of Leishmania and Trypanosoma cruzi, which have been linked to therapeutic failure.

Apoferritin and Apoferritin-Capped Metal Nanoparticles Inhibit Arginine Kinase of Trypanosoma brucei

The aim of this study was to explore the inhibitory potential of apoferritin or apoferritin-capped metal nanoparticles (silver, gold and platinum) against Trypanosomabrucei arginine kinase. The arginine kinase activity was determined in the presence and absence of apoferritin or apoferritin-capped metal nanoparticles. In addition, kinetic parameters and relative inhibition of enzyme activity were estimated. Apoferritin or apoferritin-capped metal nanoparticles’ interaction with arginine kinase of T. brucei led to a >70% reduction in the enzyme activity. Further analysis to determine kinetic parameters suggests a mixed inhibition by apoferritin or apoferritin-nanoparticles, with a decrease in V_max. Furthermore, the K_m of the enzyme increased for both ATP and L-arginine substrates. Meantime, the inhibition constant (K_i) values for the apoferritin and apoferritin-nanoparticle interaction were in the submicromolar concentration ranging between 0.062 to 0.168 nM and 0.001 to 0.057 nM, respectively, for both substrates (i.e., L-arginine and ATP). Further kinetic analyses are warranted to aid the development of these nanoparticles as selective therapeutics. Also, more studies are required to elucidate the binding properties of these nanoparticles to arginine kinase of T. brucei.

Involvement of lipids from Leishmania braziliensis promastigotes and amastigotes in macrophage activation

Leishmania are obligate protozoan parasites responsible for substantial public health problems in tropical and subtropical regions around the world, with L. braziliensis being one of the causative agents of American Tegumentary Leishmaniasis. Macrophages, fundamental cells in the innate inflammatory response against Leishmania, constitute a heterogeneous group with multiple activation phenotypes and functions. The outcome of this infection depends largely on the activation status of macrophages, the first line of mammalian defense and the major target cells for parasite replication. The importance of lipids, the major components of cell membranes, goes beyond their basic structural functions. Lipid bioactive molecules have been described in Leishmania spp., and in the recent years the knowledge about the biological relevance of lipids in particular and their relationship with the immune response is expanding. The present work analyzes the biological effects of L. braziliensis lipids from lysed promastigotes (PRO) to mimic rapid modulatory processes that could occur in the initial steps of infection or the effects of lipids from lysed and incubated promastigotes (PROinc), simulating the parasite lipid degradation processes triggered after parasite lysis that might occur in the mammalian host. To perform these studies, lipid profiles of PRO and PROinc were compared with lipids from amastigotes under similar conditions (AMA and AMAinc), and the effect of these lipid extracts were analyzed on the induction of an inflammatory response in murine peritoneal macrophages: LB induction, COX-2, iNOS and Arginase expression, TNF-α, IL-10 and NO production, Arginase activity and M1/M2 markers mRNA induction.

Pathogens MenTORing Macrophages and Dendritic Cells: Manipulation of mTOR and Cellular Metabolism to Promote Immune Escape

Myeloid cells, including macrophages and dendritic cells, represent an important first line of defense against infections. Upon recognition of pathogens, these cells undergo a metabolic reprogramming that supports their activation and ability to respond to the invading pathogens. An important metabolic regulator of these cells is mammalian target of rapamycin (mTOR). During infection, pathogens use host metabolic pathways to scavenge host nutrients, as well as target metabolic pathways for subversion of the host immune response that together facilitate pathogen survival. Given the pivotal role of mTOR in controlling metabolism and DC and macrophage function, pathogens have evolved strategies to target this pathway to manipulate these cells. This review seeks to discuss the most recent insights into how pathogens target DC and macrophage metabolism to subvert potential deleterious immune responses against them, by focusing on the metabolic pathways that are known to regulate and to be regulated by mTOR signaling including amino acid, lipid and carbohydrate metabolism, and autophagy.

The outcome of arginase activity inhibition in BALB/c mice hosting Leishmania tropica

Two species of Leishmania (L), L. tropica and L. major, are among the main causative agents of cutaneous leishmaniasis. Arginase (ARG) is an essential enzyme for cell growth, thus an attractive drug target. In this study, we tried to survey the inhibitory impact of ARG by nor-NOHA (N-ω-hydroxy-L-nor-arginine) on in vivo infection caused by L. tropica. BALB/c mice were inoculated with L. tropica^EGFP-LUC (Ltrop) or L. major^EGFP-LUC (Lmj) and then were treated by nor-NOHA. ARG inhibitor only indicated a delay in generation of a cutaneous lesion in inoculated footpad with nor-NOHA-Ltrop and nor-NOHA-Lmj. ARG activity has been significantly reduced in nor-NOHA-Ltrop group. In this group, ARG activity inhibition correlated with increased levels of nitric oxide (NO). In both inoculated mice with Ltrop or Lmj, parasite load showed a significant decrease at later steps during the CL course post-treatment. In vivo bioluminescence intensity did not show any ARG's inhibitory effect on treated-Ltrop. The findings verified that the ARG activity may partially control the L. tropica infection in BALB/c mice through reduction of parasite proliferation and parasite killing through NO generation. This effect is dose-dependent.

Immunosuppression in Experimental Chagas Disease Is Mediated by an Alteration of Bone Marrow Stromal Cell Function During the Acute Phase of Infection

After infection with Trypanosoma cruzi, the etiologic agent of Chagas disease, immunosuppression, and apoptosis of mature lymphocytes contribute to the establishment of the parasite in the host and thereby to persistence and pathology in the chronic stage of infection. In a systemic mouse model of experimental Chagas disease, we have demonstrated a strong depletion of mature B cells in the spleen during the first 2 weeks of infection. Remarkably, the decrease in this cell population commenced already in the bone marrow from infected mice and was a concomitant of an increased apoptosis in pro- and pre-B cell populations. Pro- and pre-B cells in the bone marrow showed a significant reduction accompanied by a functional disturbance of bone marrow-derived stromal cells resulting in diminished levels of IL-7, an essential factor for the development of B cell precursors. Ex vivo, stromal cells isolated from the bone marrow of infected mice had a strikingly impaired capacity to maintain the development of pro- and pre-B cells obtained from uninfected animals. Together, the reduction of an active humoral immune response during acute Chagas disease suggests to be an initial immune evasion mechanism of the parasite to establish persistent infection. Therefore, prevention of B cell depletion by rescuing the stromal cells during this early phase, could give rise to new therapeutic approaches.