Linoleic Acid Inhibits the Release of Leishmania donovani Derived Microvesicles and Decreases Its Survival in Macrophages

Computational and experimental approaches manifest the leishmanicidal potential of α-mangostin resourced from Garcinia cowa

Owing to the persistent number of parasitic deaths, Visceral leishmaniasis continues to haunt several economically weaker sections of India. The disease causes over 30,000 deaths and threatens millions annually on a global scale. The standard pentavalent antimonials, on the other hand, are associated with health adversities and disease relapse. The current study is focused on the search for the most potential natural bioactive phytocompound from the bark extract of the Northeastern Indian plant, Garcinia cowa, that shows potent anti-leishmanial properties. The High Resonance Liquid Chromatography followed by Mass Spectrometry (HR-LCMS) study followed by an in silico molecular docking using computational tools revealed that α-mangostin might potentially possess antiparasitic activity. To validate the anti-leishmanial efficacy of the compound, a cell viability assay was performed, which demonstrated the parasite-specific inhibitory activity of α-mangostin; with IC50 values ranging from 4.95 - 7.37 µM against the different forms of Leishmania donovani parasite. The flow cytometric analysis of the phytocompound treated parasites indicated an oxidative and nitrosative stress-mediated apoptotic cell death in the parasites, by the suggestive surge in nuclear fragmentation and mitochondrial dysfunction. Simultaneously, a cytokine profiling study suggested approximate two-to-three-fold upregulated levels of pro-inflammatory cytokines post-compound treatment, which is predicted to actively contribute to parasite-killing. α-mangostin was also found to reduce the chances of parasite survival by inhibiting arginase enzyme activity, which in favorable conditions facilitates its sustenance. This study thereby substantiates that α-mangostin significantly possesses anti-leishmanial potentiality that can be developed into a cure for this infectious disease.

Retinoic acid shows direct parasiticidal activity by targeting ergosterol pathway in Leishmania donovani: a potential therapeutic advancement

Visceral leishmaniasis (VL) is an infectious disease caused by Leishmania donovani parasite in Indian subcontinent and is life-threatening. It primarily inflicts the malnourished population. There is little therapeutic advancement in the last one decade or more, as the available drugs show adverse effects, complex long treatment, high cost and drug resistance. Here, in a concerted approach, we intended to address the malnutrition as well as the parasite load with a single modality. Our earlier findings show the protective effects of retinoic acid (RA) in controlling the parasite load in infected macrophages (mφ) and restores their M1 phenotype. RA also restores the levels of cellular cholesterol in infected mφ. In this process, we observed loss of ergosterol in the parasite upon treatment with RA. Hence, we hypothesized that RA, besides boosting the parasiticidal mechanism in mφ, may also target the sterol pathway in the parasite by targeting sterol 24-C methyltransferase (SMT). SMT plays an essential role in the formation of ergosterol, required for growth and viability in Leishmania species. Therefore, we predicted as well as validated the 3D structure of SMT protein and performed the quality check. RA showed -9.9 free binding energy towards SMT which is higher than any of its derivatives. The molecular dynamics showed stable conjugate and the in vitro testing showed a reduction by ∼ twofold in the parasite number upon RA treatment. Importantly, it showed a loss of ergosterol possibly due to the inhibition of SMT protein. Our finding showed direct parasiticidal function of RA which is of significance in terms of therapeutic advancement.Communicated by Ramaswamy H. Sarma.

Organ-specific immune profiling of Leishmania donovani-infected hamsters

Visceral leishmaniasis (VL) is a neglected disease with a broad spectrum of clinical manifestations and involvement of visceral organs. Organ-specific immune response against the Leishmania donovani (Ld) complex is not yet understood due to the unavailability of an appropriate experimental model. In reference to our recent work on comparing the hamster model with VL patients, it is now possible to understand immune profiling in different visceral organs. This may offer an answer to varying parasite loads in different visceral organs in the same host. Herein, we analysed a panel of immune markers (Th-2/Th-1) in visceral organs of Ld-infected hamsters and quantified parasitic load in the same tissues using qPCR assay. In spleen, liver, bone marrow and lymph node (mesenteric) from Ld-infected hamsters, the parasite burden was quantified along with mRNA expression of a panel of Th-2 and Th-1 type immune markers, namely IL-10, IL-4, Arginase-I, GATA-3, SOCS-3, IL-12, IFN-γ, iNOS, T-bet and SOCS-5. A clear dichotomy was absent between Th-2 and Th-1 type immune markers and the major players of this immune response were IFN-γ, IL-10, T-bet, GATA-3, SOCS-5 and SOCS-3.

Fatty Acid Composition and Metabolism in Leishmania Parasite Species: Potential Biomarkers or Drug Targets for Leishmaniasis?

Fatty acids have received growing interest in Leishmania biology with the characterization of the enzymes allowing the complete fatty acid synthesis of this trypanosomatid parasite. This review presents a comparative analysis of the fatty acid profiles of the major classes of lipids and phospholipids in different species of Leishmania with cutaneous or visceral tropism. Specificities relating to the parasite forms, resistance to antileishmanial drugs, and host/parasite interactions are described as well as comparisons with other trypanosomatids. Emphasis is placed on polyunsaturated fatty acids and their metabolic and functional specificities, in particular, their conversion into oxygenated metabolites that are inflammatory mediators able to modulate metacyclogenesis and parasite infectivity. The impact of lipid status on the development of leishmaniasis and the potential of fatty acids as therapeutic targets or candidates for nutritional interventions are discussed.

Phytochemical composition, bioactive properties, and toxicological profile of Tetrapleura tetraptera

The use of medicinal plants has gained renewed wide popularity in Africa, Asia, and most parts of the world because of the decreasing efficacy of synthetic drugs. Thus, natural products serve as a potent source of alternative remedy. Tetrapleura tetraptera is a medicinal plant with cultural and traditional significance in West Africa. In addition to the plant being commonly used as a spice in the preparation of traditional spicy food for postpartum care it is also widely used to constitute herbal concoctions and decoctions for treatment of diseases. This review aimed to provide an up-to-date information on the ethnomedicinal uses, pharmacological activities and phytoconstituents of T. tetraptera. Preclinical studies regarding the plant's toxicity profile were also reviewed. For this updated review, literature search was done on PubMed, Science Direct, Wiley, and Google Scholar databases using the relevant keywords. The review used a total of 106 papers that met the inclusion criteria from January 1989 - February 2022 and summarised the bioactivities that have been reported for the rich phytoconstituents of T. tetraptera studied using various chemical methods. Considering the huge report, the review focused on the antimicrobial and antiinflammatory activities of the plant extracts and isolated compounds. Aridan, aridanin and several bioactive compounds of T. tetraptera have shown pharmacological activities though their mechanisms of action are yet to be fully understood. This study also highlighted the influence of plant parts and extraction solvents on its biological activities. It also presented data on the toxicological profile of the plant extracts using different models. From cultural uses to modern pharmacological research the bioactive compounds of T. tetraptera have proved effective in infectious disease management. We hope that this paper provided a robust summary of the biological activities and toxicological profile of T. tetraptera, thus calling for more research into the pharmacological and pharmacokinetic activities of natural products to help combat the growing threat of drug resistance and provide guidelines for their ethnomedicinal uses.

Retinoic Acid Increases Cellular Cholesterol in Leishmania donovani-Infected Macrophages in an mTOR-Independent Manner

Infection with Leishmania donovani reduces cellular cholesterol and thus deprives the host cells by inhibiting its synthesis and uptake. Changes in cholesterol levels increase the chance of attachment and internalization of L. donovani in macrophages (Mϕ). Retinoic acid (RA), an important micronutrient, restores the lysosomal uptake of cholesterol in L. donovani-infected Mϕ. Importantly, mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1) increases the cellular cholesterol level by increasing expression of sterol regulatory element-binding protein 2 (SREBP2). Whether the efficacy of RA in L. donovani-infected Mϕ is mediated by mTOR is not yet established. Moreover, there are contradicting reports suggesting potential activation and inhibition of mTOR in L. donovani-infected Mϕ. Intrigued by this, we attempted to understand the RA-mediated restoration of cholesterol as well as the possible roles of mTORC1, if any. Our findings suggest that L. donovani infection impairs the synthesis of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), uptake of low-density lipoprotein receptor (LDLR), and secretion of ATP-binding cassette transporter (ABCA1) in Mϕ. L. donovani infection possibly impairs mTORC1 formation, as it inhibits the expression of regulatory-associated protein of mammalian target of rapamycin (RAPTOR). Importantly, all these are restored upon RA supplementation. RA also restores the levels of SREBP2 in L. donovani-infected Mϕ, resulting in increased cellular cholesterol and thus reducing the parasite burden. When mTORC1 was inhibited, RA exerted a similar response in L. donovani-infected Mϕ; i.e., it restored cholesterol levels and reduced the parasite burden. In summary, RA restores cholesterol levels in L. donovani-infected Mϕ and reduces the parasite burden in an mTOR-independent manner. IMPORTANCE People who reside in regions where leishmaniasis is endemic and who lack proteins, iron, zinc, and vitamin A in their diet are more prone to develop visceral leishmaniasis (VL) as a full-blown disease. Vitamin A deficiency favors the development of a parasitic infection in the human host, and the WHO recommends administering 200,000-IU doses to VL patients on admission. Additionally, Leishmania entry and its survival inside the host are achieved by utilizing host cholesterol, as all trypanosomatids lack de novo synthesis of sterol. We have already shown that RA regulates cellular cholesterol levels associated with an efficient immune response. A deficiency of retinoic acid (RA) favors the parasite in Leishmania donovani-infected macrophages by downregulating the immune response. In the present work, we observed that RA restores cellular cholesterol levels in Leishmania donovani-infected macrophages. This study proposes using RA as an immune potentiator along with standard therapy.

Human Lung Cancer (A549) Cell Line Cytotoxicity and Anti-Leishmania major Activity of Carissa macrocarpa Leaves: A Study Supported by UPLC-ESI-MS/MS Metabolites Profiling and Molecular Docking

Lung cancer and cutaneous leishmaniasis are critical diseases with a relatively higher incidence in developing countries. In this research, the activity of Carissa macrocarpa leaf hydromethanolic extract and its solvent-fractions (n-hexane, EtOAc, n-butanol, and MeOH) against the lung adenocarcinoma cell line (A549) and Leishmania major was investigated. The MeOH fraction exhibited higher cytotoxic activity (IC₅₀ 1.57 ± 0.04 μg/mL) than the standard drug, etoposide (IC₅₀ 50.8 ± 3.16 μg/mL). The anti-L. major results revealed strong growth inhibitory effects of the EtOAc fraction against L. major promastigotes (IC₅₀ 27.52 ± 0.7 μg/mL) and axenic amastigotes (29.33 ± 4.86% growth inhibition at 100 μg/mL), while the butanol fraction exerted moderate activity against promastigotes (IC₅₀ 73.17 ± 1.62), as compared with miltefosine against promastigotes (IC₅₀ 6.39 ± 0.29 μg/mL) and sodium stibogluconate against axenic amastigotes (IC₅₀ 22.45 ± 2.22 μg/mL). A total of 102 compounds were tentatively identified using UPLC-ESI-MS/MS analysis of the total extract and its fractions. The MeOH fraction was found to contain several flavonoids and flavan-3-ol derivatives with known cytotoxic properties, whereas the EtOAc fractions contained triterpene, hydroxycinnamoyl, sterol, and flavanol derivatives with known antileishmanial activity. Molecular docking of various polyphenolics of the MeOH fraction with HDAC6 and PDK3 enzymes demonstrates high binding affinity of the epicatechin 3-O-β-D-glucopyranoside and catechin-7-O-β-D-glucopyranoside toward HDAC6, and procyanidin C2, procyanidin B5 toward PDK3. These results are promising and encourage the pursuit of preclinical research using C. macrocarpa's MeOH fraction as anti-lung cancer and the EtOAc fraction as an anti-L. major drug candidates.

Retinoic acid increases the cellular cholesterol predominantly in a mTOR-independent manner

Retinoic acid (RA) plays a role in the mounting immune response and controls several functions of the human body, including cholesterol homeostasis. The synthesis, uptake, and efflux of cellular cholesterol are significantly linked to the mammalian target of rapamycin complex-1 (mTORC1). Activation of mTORC1 promotes the synthesis and uptake of the cholesterol and suppresses its efflux, thus causing accumulation of cellular cholesterol. It is intriguing to know the effect of a high dose of RA on cholesterol accumulation in macrophages (mφ) and whether it is via mTOR activation. It is important to note that the long-term treatment of RA in humans is safe. Therefore, we chose a high dose of RA to observe its effect, which may be implicated in diseases like visceral leishmaniasis, where cholesterol deficiency is established. In the present study, we found the increased expression of RAPTOR, a regulatory component of the mTORC1 complex, in mφ upon treatment with RA. We observed the increased expression of SREBP2, LDLR, and PCSK9 in RA-treated mφ under sufficient cholesterol conditions, which further increased cellular cholesterol levels. Notably, their expressions were decreased when the mTOR pathway was inhibited by rapamycin. However, treatment with rapamycin did not result in the loss of cellular cholesterol in RA-treated mφ. Comparison with rapamycin-treated mφ suggests that RA induces cellular cholesterol levels in a mTORC1-independent manner.

Tissue Specific Dual RNA-Seq Defines Host-Parasite Interplay in Murine Visceral Leishmaniasis Caused by Leishmania donovani and Leishmania infantum

Visceral leishmaniasis is associated with hepato-splenomegaly and altered immune and hematological parameters in both preclinical animal models and humans. We studied mouse experimental visceral leishmaniasis caused by Leishmania infantum and Leishmania donovani in BALB/c mice using dual RNA-seq to investigate the transcriptional response of host and parasite in liver and spleen. We identified only 4 species-specific parasite expressed genes (SSPEGs; log2FC >1, FDR <0.05) in the infected spleen, and none in the infected liver. For the host transcriptome, we found 789 differentially expressed genes (DEGs; log2FC >1, FDR <0.05) in the spleen that were common to both infections, with IFNγ signaling and complement and coagulation cascade pathways highly enriched, and an additional 286 and 186 DEGs that were selective to L. donovani and L. infantum infection, respectively. Among those, there were network interactions between genes of amino acid metabolism and PPAR signaling in L. donovani infection and increased IL1β and positive regulation of fatty acid transport in L. infantum infection, although no pathway enrichment was observed. In the liver, there were 1,939 DEGs in mice infected with either L. infantum or L. donovani in comparison to uninfected mice, and the most enriched pathways were IFNγ signaling, neutrophil mediated immunity, complement and coagulation, cytokine-chemokine responses, and hemostasis. Additionally, 221 DEGs were selective in L. donovani and 429 DEGs in L. infantum infections. These data show that the host response for these two visceral leishmaniasis infection models is broadly similar, and ∼10% of host DEGs vary in infections with either parasite species. IMPORTANCE Visceral leishmaniasis (VL) is caused by two species of Leishmania parasites, L. donovani in the Old World and L. infantum in the New World and countries bordering the Mediterranean. Although cardinal features such as hepato-splenomegaly and alterations in blood and immune function are evident, clinical presentation may vary by geography, with for example severe bleeding often associated with VL in Brazil. Although animal models of both L. donovani and L. infantum have been widely used to study disease pathogenesis, a direct side-by-side comparison of how these parasites species impact the infected host and/or how they might respond to the stresses of mammalian infection has not been previously reported. Identifying common and distinct pathways to pathogenesis will be important to ensure that new therapeutic or prophylactic approaches will be applicable across all forms of VL.

Retinoic acid restores the levels of cellular cholesterol in Leishmania donovani infected macrophages by increasing npc1 and npc2 expressions

Visceral leishmaniasis (VL) is a fatal form among all forms of leishmaniasis and is caused by visceralization of the Leishmania donovani (Ld) parasite to the critical organs. Mild to severe malnutrition is common in VL patients and the deficiency of retinoic acid (RA), an important micronutrient, results in a compromised state of immune response in macrophages (mφ) leading to the increased parasite load. In the continuation of our earlier work, we observed loss of cellular cholesterol in infected mφ in the absence of RA i.e., upon inhibition of RALDH pathway. Moreover, the Leishmania utilizes host cholesterol for the establishment of infection and causes a decrease in the expressions of Niemann-Pick C2 (npc2) and Niemann-Pick C1 (npc1) genes involved in the uptake of extracellular cholesterol. This results in reduced levels of cellular cholesterol in infected mφ. Intrigued by this, as the first sign of our hypothesis, we investigated the presence of RA Response Element (RARE) sequences in the upstream of npc1 and npc2 genes. To functionally confirm this, we measured their expressions and the levels of cellular cholesterol in Ld infected mφ in the absence (i.e., using an inhibitor of RALDH pathway) and presence of RA. We found restoration of the levels of cellular cholesterol in infected mφ under the supplementation of RA resulting in the decreased parasite load. Hence, the supplementation of RA with the standard therapy and/or preventive use of RA could be potentially an advancement in the treatment and cure of VL patients.

Fecal metabolomic analysis of rabbits infected with Eimeria intestinalis and Eimeria magna based on LC-MS/MS technique

Rabbit coccidiosis is a common parasitic disease leading to economic losses in the rabbit industry. The intestinal flora plays a key role in pathogenesis of coccidiosis, and fecal metabolome mediates host-microbiome interactions as a functional readout of the gut microbiome. In this study, the E. intestinalis-infected and E. magna-infected rabbit models were established to investigate metabolic alterations and metabolic pathways based on LC-MS/MS technique for the first time. Multivariate OPLS-DA analysis was performed to explore differential metabolites. In total, 288 metabolites were detected from infected and uninfected rabbits. The level of 33 metabolites increased and 4 decreased in rabbits infected with E. intestinalis. Eight pathways were significantly perturbed during E. intestinalis infection including biosynthesis of unsaturated fatty acids, fatty acid biosynthesis, etc. After rabbits infected with E. magna, 13 metabolites were altered and 7 metabolic pathways were dysregulated. These metabolites and metabolic pathways were mainly involved in tuberculosis, parathyroid hormone synthesis, etc. Besides, 25 metabolites differed in abundance between E. intestinalis infection group and E. magna infection group, the major perturbed metabolic pathways were lipid metabolism and endocrine system, respectively. In general, it is confirmed that E. intestinalis and E. magna infection destroyed the intestinal flora, which caused corresponding changes in metabolites, and provide novel insights into the molecular mechanisms of rabbit-parasite interactions.

Long Chain Fatty Acids as Modulators of Immune Cells Function: Contribution of FFA1 and FFA4 Receptors

Long-chain fatty acids are molecules that act as metabolic intermediates and constituents of membranes; however, their novel role as signaling molecules in immune function has also been demonstrated. The presence of free fatty acid (FFA) receptors on immune cells has contributed to the understanding of this new role of long-chain fatty acids (LCFAs) in immune function, showing their role as anti-inflammatory or pro-inflammatory molecules and elucidating their intracellular mechanisms. The FFA1 and FFA4 receptors, also known as GPR40 and GPR120, respectively, have been described in macrophages and neutrophils, two key cells mediating innate immune response. Ligands of the FFA1 and FFA4 receptors induce the release of a myriad of cytokines through well-defined intracellular signaling pathways. In this review, we discuss the cellular responses and intracellular mechanisms activated by LCFAs, such as oleic acid, linoleic acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), in T-cells, macrophages, and neutrophils, as well as the role of the FFA1 and FFA4 receptors in immune cells.

Metabolomic Profiles in the Intestine of Shrimp Infected by White Spot Syndrome Virus and Antiviral Function of the Metabolite Linoleic Acid in Shrimp

White spot syndrome virus (WSSV) is a threatening pathogenic virus in shrimp culture, and at present, no effective strategy can prevent and control the disease. Intestinal flora and its metabolites are important for the resistance of shrimp to lethal pathogenic viruses. However, the changes of metabolites in the shrimp intestines after WSSV infection remain unclear. We established an artificial oral infection method to infect shrimp with WSSV and analyzed the metabolites in intestinal content of shrimp by HPLC and tandem mass spectrometry. A total of 78 different metabolites and five different metabolic pathways were identified. Among them, we found that the content of linoleic acid, an unsaturated fatty acid, increased significantly after WSSV infection, indicating that linoleic acid might be involved in antiviral immunity in shrimp. Further study showed that, after oral administration of linoleic acid, WSSV proliferation decreased evidently in the shrimp, and survival rate of the shrimp increased significantly. Mechanical analysis showed that linoleic acid directly bound to WSSV virions and inhibited the viral replication. Linoleic acid also promoted the expression of antimicrobial peptides and IFN-like gene Vago5 by activating the ERK-NF-κB signaling pathway. Our results indicated that WSSV infection caused metabolomic transformation of intestinal microbiota and that the metabolite linoleic acid participated in the immune response against WSSV in shrimp.