Crotoxin stimulates an M1 activation profile in murine macrophages during Leishmania amazonensis infection

Crotoxin modulates Encephalitozoon cuniculi-infected macrophages toward the M1 microbicidal profile

Crotoxin (CTX), a bioactive extract from the snake Crotalus durissus terrificus, has antibacterial, antitumor, and anti-inflammatory properties. Microsporidia are opportunistic, obligate intracellular fungi that infect vertebrates and invertebrates and are highly resistant to conventional drugs. They can also subvert the microbicidal activity of M1 macrophages to an M2 profile, which is more favorable for the pathogen. Thus, in this study, we evaluated the effects of CTX on the viability of spores of the microsporidium Encephalitozoon cuniculi, as well as on the microbicidal activity of macrophages in vitro. E. cuniculi spores were treated with two concentrations of CTX (2.4 and 4.8 μg/mL) and cultivated in RK-13 cells for viability analysis. Additionally, peritoneal adherent cells (APerC), obtained from peritoneal washes of BALB/c mice, were infected with spores of E. cuniculi for 1 h and treated with CTX for 3 h. The profile of macrophages, cytokine production, viability of macrophages, and proliferative capacity of spores were subsequently evaluated. Treatment of E. cuniculi spores with CTX had no fungicidal or fungistatic effects. Compared to the macrophages in the control group, macrophages infected with E. cuniculi and treated with 2.4 μg/mL CTX presented an increase in the M1 profile, more necrosis, and greater production of the cytokines TNF-α and IL-6, and the spores obtained from these macrophages presented a reduction in proliferative capacity. These results indicated that CTX modulated the M1 profile of macrophages infected with E. cuniculi, resulting in greater production of proinflammatory cytokines and stronger microbicidal activity.

Molecular interaction assays in silico of crotapotin from Crotalus durissus terrificus against the molecular target trypanothione reductase from Leishmania braziliensis

Background

Leishmaniasis is a neglected disease that mainly affects impoverished populations and receives limited attention from governments and research institutions. Current treatments are based on antimonial therapies, which present high toxicity and cause significant side effects, such as cardiotoxicity and hepatotoxicity. This study proposes using crotapotin, isolated from Crotalus durissus terrificus venom, as a potential inhibitor of the enzyme trypanothione reductase from Leishmania braziliensis (LbTR).

Methods

In silico assays were conducted to evaluate the interaction of crotapotin with LbTR using molecular docking and molecular dynamics techniques. Recombinant LbTR was expressed in E. coli, and its enzymatic activity was confirmed. The inhibitory action of crotapotin on LbTR was then tested in enzymatic assays.

Results

The stability of these interactions was confirmed over 200 ns molecular dynamics simulations, with a clustering analysis using the GROMACS method revealing a total of 12 distinct clusters. The five most representative clusters showed low RMSD values, indicating high structural stability of the LbTR-crotapotin complex. In particular, cluster 1, with 3,398 frames and an average RMSD of 0.189 nm from the centroid, suggests a dominant stable conformation of the complex. Additional clusters maintained average RMSD values between 0.173 nm and 0.193 nm, further reinforcing the robustness of the complex under physiological conditions. Recombinant LbTR expression was successful, yielding 4.8 mg/L with high purity, as verified by SDS-PAGE. In the enzymatic assays, crotapotin partially inhibited LbTR activity, with an IC50 of 223.4 μM.

Conclusion

The in silico findings suggest a stable and structured interaction between crotapotin and LbTR, with low structural fluctuation, although the inhibition observed in in vitro assays was moderate. These results indicate the potential of crotapotin as a promising basis for developing specific LbTR inhibitors, contributing to the bioprospecting of new antiparasitic agents.

Antischistosomal Potential of Animal-Derived Natural Products and Compounds

Schistosomiasis is a neglected tropical disease that affects over 240 million people worldwide. Currently, praziquantel is the only drug recommended by the World Health Organization for treatment. However, cases of drug resistance have been reported, which indicates an urgent need for new therapeutics. In this context, natural compounds represent valuable sources of pharmacological substances. Plant-derived natural products have been greatly explored for their potential antischistosomal activity, while animal-derived compounds have received little attention. Recent advances in the biotechnology field allow the wide exploration of animal-derived compounds in drug discovery, which may represent a cost-effective option to find bioactive molecules also against Schistosoma mansoni and other parasites. This review highlights the research into animal-derived products and compounds that have already been tested against schistosomes. Phenotypic effects on schistosomes have been observed upon incubation with some of these substances, which may, therefore, represent possible candidates to be used in the development of new drugs. Overall, these studies advance the discovery of antischistosomal compounds by exploring a yet understudied natural resource. The present review also discusses the challenges of testing animal-derived products and provides examples of the experimental in vitro testing of different selected animal natural products against S. mansoni.

In vitro immunomodulatory effects of Caryocar villosum oil on murine macrophages

Macrophages undergo activation in response to multiple stimuli, including pathogens, growth factors and natural products. The inflammatory response and oxidative stress play critical roles in such macrophage activation. Some natural products reportedly promote immunoregulatory effects and the control of macrophage activation. Caryocar villosum (Cv), a native amazon plant, contains compounds that are an important source of molecules capable of macrophage activation. Herein, we demonstrate the immunomodulatory effects of oil obtained from Caryocar villosum (CvO) on macrophages. Macrophages were treated with varying concentrations of CvO, and resulting cellular morphological and functional changes were evaluated, including the production of nitric oxide (NO), reactive oxygen species (ROS), cytokines and phagocytic activity. Treatment of cells with 50 and 100 μg/mL CvO induced morphological and physiological alterations in the macrophages, such as increased cell surface and phagocytic activity. Additionally, treatment increased the productions of inflammatory cytokines (INF-γ, TNF-α, IL-6) and anti-inflammatory cytokines (IL-17 and IL-10) by macrophages, and significantly decreased ROS levels. In conclusion, these data suggest that, due to molecular diversity, CvO promoted an immunomodulatory effect on macrophages, mediated by an increased production of cytokines, and inhibition of ROS generation and phagocytic activity. Thus, CvO presents potential as a therapeutic agent for the treatment of inflammatory and non-inflammatory diseases.

Unlocking the potential of snake venom-based molecules against the malaria, Chagas disease, and leishmaniasis triad

Malaria, leishmaniasis and Chagas disease are vector-borne protozoal infections with a disproportionately high impact on the most fragile societies in the world, and despite malaria-focused research gained momentum in the past two decades, both trypanosomiases and leishmaniases remain neglected tropical diseases. Affordable effective drugs remain the mainstay of tackling this burden, but toxicicty, inneficiency against later stage disease, and drug resistance issues are serious shortcomings. One strategy to overcome these hurdles is to get new therapeutics or inspiration in nature. Indeed, snake venoms have been recognized as valuable sources of biomacromolecules, like peptides and proteins, with antiprotozoal activity. This review highlights major snake venom components active against at least one of the three aforementioned diseases, which include phospholipases A2, metalloproteases, L-amino acid oxidases, lectins, and oligopeptides. The relevance of this repertoire of biomacromolecules and the bottlenecks in their clinical translation are discussed considering approaches that should increase the success rate in this arduous task. Overall, this review underlines how venom-derived biomacromolecules could lead to pioneering antiprotozoal treatments and how the drug landscape for neglected diseases may be revolutionized by a closer look at venoms. Further investigations on poorly studied venoms is needed and could add new therapeutics to the pipeline.

Crotoxin modulates inflammation and macrophages' functions in a murine sepsis model

Sepsis is a syndrome of physiological and biochemical abnormalities induced by an infection that represents a major public health concern. It involves the early activation of inflammatory responses. Crotoxin (CTX), the major toxin of the South American rattlesnake Crotalus durissus terrificus venom, presents longstanding anti-inflammatory properties. Since immune system modulation may be a strategic target in sepsis management, and macrophages' functional and secretory activities are related to the disease's progression, we evaluated the effects of CTX on macrophages from septic animals. Balb/c male mice submitted to cecal ligation and puncture (CLP) were treated with CTX (0.9 μg/animal, subcutaneously) 1 h after the procedure and euthanized after 6 h. We used plasma samples to quantify circulating cytokines and eicosanoids. Bone marrow differentiated macrophages (BMDM) were used to evaluate the CTX effect on macrophages' functions. Our data show that CTX administration increased the survival rate of the animals from 40% to 80%. Septic mice presented lower plasma concentrations of IL-6 and TNF-α after CTX treatment, and higher concentrations of LXA₄, PGE_2, and IL-1β. No effect was observed in IL-10, IFN-γ, and RD1 concentrations. BMDM from septic mice treated with CTX presented decreased capacity of E. coli phagocytosis, but sustained NO and H₂O₂ production. We also observed higher IL-6 concentration in the culture medium of BMDM from septic mice, and CTX induced a significant reduction. CTX treatment increased IL-10 production by macrophages as well. Our data show that the protective effect of CTX in sepsis mortality involves modulation of macrophage functions and inflammatory mediators' production.

Effect of Isolated Proteins from Crotalus Durissus Terrificus Venom on Leishmania (Leishmania) Amazonensis-Infected Macrophages

BACKGROUND

Cutaneous and mucocutaneous leishmaniasis are parasitic diseases characterized by skin manifestations. In Brazil, Leishmania (Leishmania) amazonensis is one of the etiological agents of cutaneous leishmaniasis. The therapeutic arsenal routinely employed to treat infected patients is unsatisfactory, especially for pentavalent antimonials, as they are often highly toxic, poorly tolerated and of variable effectiveness. This study aimed to evaluate in vitro the leishmanicidal activity of toxins isolated from Crotalus durissus terrificus venom as a new approach for the treatment of leishmaniasis.

METHODS

The comparative effects of crotamine, crotoxin, gyrotoxin, convulxin and PLA2 on bone marrow-derived macrophages infected with L. (L.) amazonensis as well as the release of TGF-β from the treated macrophages were studied.

RESULTS AND DISCUSSION

Crotamine had the strongest inhibitory effect on parasite growth rate (IC50: 25.65±0.52 μg/mL), while convulxin showed the weakest inhibitory effect (IC50: 52.7±2.21 μg/mL). In addition, TGF-β was significantly reduced after the treatment with all toxins evaluated.

CONCLUSION

The Crotalus durissus terrificus toxins used in this study displayed significant activity against L. (L.) amazonensis, indicating that all of them could be a potential alternative for the treatment of cutaneous leishmaniasis.

Effects of crotoxin, a neurotoxin from Crotalus durissus terrificus snake venom, on human endothelial cells

Vascular endothelium plays an important modulatory role due to the production of molecules that mediate vasomotricity, inflammation, and leukocyte adhesion and rolling. Here we addressed whether crotoxin (25-200 μg/mL) - the main component of Crotalus durissus terrificus snake venom - interferes with cell viability, apotosis/necrosis, and cell response to oxidative stress in human umbilical vein endothelial cells (HUVEC) in vitro. We also examined whether crotoxin alters the levels of interleukins, adhesion molecules, and endothelial vasoactive factors in HUVEC cells treated or not with lipopolysaccharide (LPS; 1 μg/mL; 24 h). Crotoxin was not cytotoxic towards HUVEC cells, and downregulated the LPS-induced production of adhesion molecules (VCAM-1, ICAM-1, and E-selectin), vasoactive factors (endothelin-1 and prostaglandin I2), and interleukins (IL-6, IL-8, and IL1β), as well as protected cells against H₂O₂-induced oxidative stress. Hence, crotoxin played anti-inflammatory, antioxidant, immunomodulating, and vasoactive actions on HUVEC cells, in vitro. Considering that the initial stages of atherosclerosis is characterized by vasoconstriction, increased levels of adhesion molecules, inflammatory cytokines, and oxidative stress in the vascular endothelium; and crotoxin downmodulated all these events, our findings indicate that the actions of crotoxin here demonstrated suggest that it may have an anti-atherogenic action in vivo, which deserves to be tested in future studies.

Intradermal Application of Crotamine Induces Inflammatory and Immunological Changes In Vivo

Crotamine is a single-chain polypeptide with cell-penetrating properties, which is considered a promising molecule for clinical use. Nevertheless, its biosafety data are still scarce. Herein, we assessed the in vivo proinflammatory properties of crotamine, including its local effect and systemic serum parameters. Sixty male Wistar rats were intradermically injected with 200, 400 and 800 µg crotamine and analyzed after 1, 3 and 7 days. Local effect of crotamine was assessed by determination of MPO and NAG activities, NO levels and angiogenesis. Systemic inflammatory response was assessed by determination of IL-10, TNF-α, CRP, NO, TBARS and SH groups. Crotamine induced macrophages and neutrophils chemotaxis as evidenced by the upregulation of both NAG (0.5–0.6 OD/mg) and MPO (0.1–0.2 OD/mg) activities, on the first and third day of analysis, respectively. High levels of NO were observed for all concentrations and time-points. Moreover, 800 μg crotamine resulted in serum NO (64.7 μM) and local tissue NO (58.5 μM) levels higher or equivalent to those recorded for their respective histamine controls (55.7 μM and 59.0 μM). Crotamine also induced a significant angiogenic response compared to histamine. Systemically, crotamine induced a progressive increase in serum CRP levels up to the third day of analysis (22.4–45.8 mg/mL), which was significantly greater than control values. Crotamine (400 μg) also caused an increase in serum TNF-α, in the first day of analysis (1095.4 pg/mL), however a significant increase in IL-10 (122.2 pg/mL) was also recorded for the same time-point, suggesting the induction of an anti-inflammatory effect. Finally, crotamine changed the systemic redox state by inducing gradual increase in serum levels of TBARS (1.0–1.8 μM/mL) and decrease in SH levels (124.7–19.5 μM/mL) throughout the experimental period of analysis. In summary, rats intradermally injected with crotamine presented local and systemic acute inflammatory responses similarly to histamine, which limits crotamine therapeutic use on its original form.

Macrophage Polarization in Leishmaniasis: Broadening Horizons

Leishmaniasis is a vector-borne neglected tropical disease that affects more than 700,000 people annually. Leishmania parasites cause the disease, and different species trigger a distinct immune response and clinical manifestations. Macrophages are the final host cells for the proliferation of Leishmania parasites, and these cells are the key to a controlled or exacerbated response that culminates in clinical manifestations. M1 and M2 are the two main macrophage phenotypes. M1 is a pro-inflammatory subtype with microbicidal properties, and M2, or alternatively activated, is an anti-inflammatory/regulatory subtype that is related to inflammation resolution and tissue repair. The present review elucidates the roles of M1 and M2 polarization in leishmaniasis and highlights the role of the salivary components of the vector and the action of the parasite in the macrophage plasticity.

Biochanin a Enhances the Defense Against Salmonella enterica Infection Through AMPK/ULK1/mTOR-Mediated Autophagy and Extracellular Traps and Reversing SPI-1-Dependent Macrophage (MΦ) M2 Polarization

A novel treatment regimen for bacterial infections is the pharmacological enhancement of the host's immune defenses. We demonstrated that biochanin A (BCA), an isoflavone constituent in some plants, could enhance both intra- and extracellular bactericidal activity of host cells. First, BCA could induce a complete autophagic response in nonphagocytic cells (HeLa) or macrophages (MΦ) via the AMPK/ULK1/mTOR pathway and Beclin-1-dependent manner, and BCA enhanced the killing of invading Salmonella by autophagy through reinforcing ubiquitinated adapter protein (LRSAM1, NDP52 and p62)-mediated recognition of intracellular bacteria and through the formation of autophagolysosomes. Second, we demonstrated that BCA could enhance the release of MΦ extracellular traps (METs) to remove extracellular Salmonella also via the AMPK/ULK1/mTOR pathway, not through reactive oxygen species (ROS) pathway. Furtherly, in a Salmonella-infected mouse model, BCA treatment increased intra- and extracellular bactericidal activity through the strengthening autophagy and MET production, respectively, in peritoneal MΦ, liver and spleen tissue. Additionally, our findings showed that BCA downregulated SPI-1 (Salmonella pathogenicity island 1) expression during Salmonella infection in vitro and in vivo to reverse the MΦ M2 polarization, which was different from the MΦ M1 phenotype caused by most of bacteria infection. Together, these findings suggest that BCA has an immunomodulatory effect on Salmonella-infected host cells and enhances their bactericidal activity in vitro and in vivo through autophagy, extracellular traps and regulation of MΦ polarization.

In vitro antileishmanial effects of Physalis angulata root extract on Leishmania infantum

OBJECTIVE

In the present study, we evaluated the effects of the aqueous extract of Physalis angulata root (AEPa) on Leishmania infantum proliferation, morphology, and the driving mechanism in leishmanicidal activity and modulatory action on macrophages.

METHODS

L. infantum promastigotes were treated with 50 and 100 µg/mL AEPa for 72 h and then antipromastigote assay was performed by counts in a Newbauer chamber, morphological changes were analyzed by transmission electron microscopy and the mechanism of the leishmanicidal activity was detected. In addition, macrophages were infected with L. infantum and were used to evaluate anti-amastigote activity of AEPa and effects of AEPa on cytokine secretion after 72-hour treatment.

RESULTS

Treatment with AEPa reduced the numbers of L. infantum promastigotes (50% inhibitory concentration (IC₅₀) = 65.9 μg/mL; selectivity index (SI) = 22.1) and amastigotes (IC₅₀ = 37.9 μg/mL; SI = 38.5) compared with the untreated control. Amphotericin B reduced 100% of the promastigote numbers after 72 h of treatment (IC₅₀ = 0.2 μg/mL). AEPa induced several morphological changes and increased the production of reactive oxygen species and apoptotic death in promastigotes after treating for 72 h. AEPa (100 μg/mL) promoted tumor necrosis factor-α secretion in macrophages infected with L. infantum after 72 h of treatment, but did not induce an increase in this cytokine in noninfected macrophages. In addition, AEPa showed no cytotoxic effect on J774-A1 cells (50% cytotoxic concentration >1000 μg/mL).

CONCLUSION

AEPa presented antileishmanial activity against the promastigotes and amastigotes of L. infantum without macrophage cytotoxicity; these results show that natural products such as P. angulata have leishmanicidal potential and in the future may be an alternative treatment for leishmaniasis.