Plant lectins ConBr and CFL modulate expression toll-like receptors, pro-inflammatory cytokines and reduce the bacterial burden in macrophages infected with Salmonella enterica serovar Typhimurium

Reference genes for gene expression profiling in mouse models of Listeria monocytogenes infection

RT-qPCR dissects transcription-based processes but requires reference genes (RGs) for data normalization. This study prospected RGs for mouse macrophages (pMØ) and spleen infected with Listeria monocytogenes. The pMØ were infected in vitro with L. monocytogenes or vehicle for 4 h. Mice were injected with L. monocytogenes (or vehicle) and euthanized 24 h post-injection. The RGs came from a multispecies primer set, from the literature or designed here. The RG ranking relied on GeNorm, NormFinder, BestKeeper, Delta-CT and RefFinder. B2m-H3f3a-Ppia were the most stable RGs for pMØ, albeit RG indexes fine-tuned estimations of cytokine relative expression. Actβ-Ubc-Ppia were the best RGs for spleen but modestly impacted the cytokine relative expression. Hence, mouse models of L. monocytogenes require context-specific RGs for RT-qPCR, thus reinforcing its paramount contribution to accurate gene expression profiling.

Plant lectins: A new antimicrobial frontier

Pathogenic bacteria, viruses, fungi, parasites, and other microbes constantly change to ensure survival. Several pathogens have adopted strict and intricate strategies to fight medical treatments. Many drugs, frequently prescribed to treat these pathogens, are becoming obsolete and ineffective. Because pathogens have gained the capacity to tolerate or resist medications targeted at them, hence the term antimicrobial resistance (AMR), in that regard, many natural compounds have been routinely used as new antimicrobial agents to treat infections. Thus, plant lectins, the carbohydrate-binding proteins, have been targeted as promising drug candidates. This article reviewed more than 150 published papers on plant lectins with promising antibacterial and antifungal properties. We have also demonstrated how some plant lectins could express a synergistic action as adjuvants to boost the efficacy of obsolete or abandoned antimicrobial drugs. Emphasis has also been given to their plausible mechanism of action. The study further reports on the immunomodulatory effect of plant lectins and how they boost the immune system to curb or prevent infection.

Anti-infective activity of Cratylia argentea lectin (CFL) against experimental infection with virulent Listeria monocytogenes in Swiss mice

BACKGROUND

The lectin from Cratylia argentea (CFL) is able to modulate the immune system response and is thus a potential phytotherapeutic substance.

HYPOTHESIS/PURPOSE

In this study, we investigated the role of CFL on control of bacterial infection caused by Listeria monocytogenes, the causative agent of human listeriosis.

STUDY DESIGN

Swiss mice were infected with L. monocytogenes and then treated with CFL.

METHODS

Adult Swiss mice weighing with 30-40 g were infected intraperitoneally with a bacterial suspension (0.2 ml; 1 × 10⁷ CFU/ml). After 30 min, the mice were treated with CFL intravenously at concentrations of 0.1 or 10 mg/kg. Control mice received phosphate-buffered saline (PBS). The animals were euthanized 24 h after infection.

RESULTS

We observed that i.v. administration of CFL to Swiss mice did not cause acute toxicity, and reduced the leukocyte counts in the bloodstream 24 h after infection with virulent L. monocytogenes. There was a reduction in the bacterial burden within peritoneal macrophages after infection in CFL-treated mice. Accordingly, the bacterial counts in the bloodstream, spleen and liver also decreased in comparison with the PBS group. Histological damage in the spleen and liver was lower in mice that received CFL treatment. In vitro antimicrobial assays demonstrated that CFL does not inhibit the growth of L. monocytogenes. The mRNA expression of the anti-inflammatory cytokine IL-10 was enhanced with CFL treatment after infection.

CONCLUSION

The lectin from C. argentea (CFL) has immunomodulatory and anti-infective properties of pharmacological interest for control of infectious diseases.

Mechanistic insight into immunomodulatory effects of food-functioned plant secondary metabolites

Medicinally important plant-foods offer a balanced immune function, which is essential for protecting the body against antigenic invasion, mainly by microorganisms. Immunomodulators play pivotal roles in supporting immune function either suppressing or stimulating the immune system's response to invading pathogens. Among different immunomodulators, plant-based secondary metabolites have emerged as high potential not only for immune defense but also for cellular immunoresponsiveness. These natural immunomodulators can be developed into safer alternatives to the clinically used immunosuppressants and immunostimulant cytotoxic drugs which possess serious side effects. Many plants of different species have been reported to possess strong immunomodulating properties. The immunomodulatory effects of plant extracts and their bioactive metabolites have been suggested due to their diverse mechanisms of modulation of the complex immune system and their multifarious molecular targets. Phytochemicals such as alkaloids, flavonoids, terpenoids, carbohydrates and polyphenols have been reported as responsible for the immunomodulatory effects of several medicinal plants. This review illustrates the potent immunomodulatory effects of 65 plant secondary metabolites, including dietary compounds and their underlying mechanisms of action on cellular and humoral immune functions in in vitro and in vivo studies. The clinical potential of some of the compounds to be used for various immune-related disorders is highlighted.

Antiinflammatory and antiinfective effect of caffeine in a mouse model of disseminated salmonellosis

Caffeine has been reported for its antiinflammatory properties by stimulating phagocytosis. In this study, we investigated the antiinflammatory and antiinfective potential of caffeine in murine macrophage cell cultures and Swiss mice infected with virulent Salmonella enterica serotype typhimurium. Peritoneal macrophages (pMØ) were treated with caffeine on 96-well plates for 24 hr and then infected with Salmonella for 4 hr. In another experiment, the pMØ were first infected with the bacterium for 4 hr and then treated with caffeine for 24 hr. In addition, Swiss mice were inoculated, intraperitoneally, with S. typhimurium and then received caffeine intravenously. Control groups received phosphate-buffered saline (PBS) or dexamethasone. We found that treatments with caffeine increased the macrophage cell viability and reduced the intracellular bacterial load. The administration of caffeine to Swiss mice reduced the infiltration of leukocytes into the peritoneal cavity after the bacterial challenge. Furthermore, the bacterial burdens in the peritoneal fluid, bloodstream, spleen, and liver were decreased by caffeine treatment. The expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), IL-6, and inducible nitric oxide synthase (iNOs) were down-regulated after infection in caffeine-treated mice. We can conclude that caffeine has both antiinflammatory and antiinfective properties that can be useful for management of bacterial infections along with antibiotics.

Immunomodulatory Effects of Jacalin, a Dietary Plant Lectin on the Peripheral Blood Mononuclear Cells (PBMCs)

The tumor microenvironment that refers to the tumor's surroundings is a key modulator of tumor growth and invasion. The tumor-derived signals are known to downregulate the anti-tumor effects of the effector cells present in the TME. Thus, the cross-talk between the tumor cells with the surrounding immune cells helps in evading the tumor surveillance as well as aiding in tumor growth and proliferation. Hence, knowledge regarding the effects of drugs/compound on the tumor-stromal interactions is gaining importance. In the present study, the effects of jacalin, a dietary lectin on the proliferation and cytokine production of peripheral blood mononuclear cells (PBMCs), are investigated. Jacalin was shown to act as a mitogen of PBMCs, the key cytokine secreting immune cells. Also, jacalin initially induced increased mRNA expression of pro-inflammatory cytokine IFN-γ; however, prolonged stimulation of PBMCs resulted in increased expression of anti-inflammatory cytokine, mainly TGF-β. Furthermore, 6 h jacalin prestimulated PBMCs (Jac-PBMCs) were shown to inhibit HeLa cell proliferation while 24 h Jac-PBMCs were found to favor tumor growth. Thus, it may be postulated that while jacalin initially polarizes the PBMCs to hinder the tumor growth, after a stipulated time point, interaction of jacalin with PBMCs can lead to an immunosuppressive TME that may probably assist in tumor growth and progression.

Anti-inflammatory activity of caffeine (1,3,7-trimethylxanthine) after experimental challenge with virulent Listeria monocytogenes in Swiss mice

BACKGROUND

Immunomodulatory therapies are claimed to enhance antimicrobial immunity and counterbalance antimicrobial resistance mechanisms of pathogenic bacteria.

PURPOSE

To investigate whether caffeine can be useful for control of inflammation derived from experimental systemic infection with Listeria monocytogenes.

METHODS

Peritoneal macrophages (pMØ) from Swiss mice were cultured with caffeine in 96-well plates, and then infected with virulent L. monocytogenes 619. In another experiment, the pMØ were first infected with the bacterium and then treated with caffeine. Swiss mice were inoculated intraperitoneally with L. monocytogenes and then treated intravenously with caffeine (0.05; 0.5 or 5 mg/Kg).

RESULTS

Caffeine did not exert direct antibacterial activity in vitro against L. monocytogenes. Macrophages exposed to caffeine before or after infection with L. monocytogenes had increased cell viability, although the intracellular bacterial loads were similar to the control groups. Caffeine treatments of Swiss mice reduced leukocyte infiltration into the peritoneal cavity after L. monocytogenes infection. However, the bacterial burden was reduced in the spleen and liver. The mRNA expressions of IL-1β, IL-6 and the enzyme inducible nitric oxide synthase (iNOS) were reduced whereas IL-10 was increased.

CONCLUSION

Caffeine has an anti-infectious potential and ameliorated infection-derived inflammation following experimental infection with L. monocytogenes.

Exploring lectin-glycan interactions to combat COVID-19: Lessons acquired from other enveloped viruses

The emergence of a new human coronavirus (SARS-CoV-2) has imposed great pressure on the health system worldwide. The presence of glycoproteins on the viral envelope opens a wide range of possibilities for application of lectins to address some urgent problems involved in this pandemic. In this work, we discuss the potential contributions of lectins from non-mammalian sources in the development of several fields associated with viral infections, most notably COVID-19. We review the literature on the use of non-mammalian lectins as a therapeutic approach against members of the Coronaviridae family, including recent advances in strategies of protein engineering to improve their efficacy. The applications of lectins as adjuvants for antiviral vaccines are also discussed. Finally, we present some emerging strategies employing lectins for the development of biosensors, microarrays, immunoassays and tools for purification of viruses from whole blood. Altogether, the data compiled in this review highlights the importance of structural studies aiming to improve our knowledge about the basis of glycan recognition by lectins and its repercussions in several fields, providing potential solutions for complex aspects that are emerging from different health challenges.

Perspectives for the use of latex peptidases from Calotropis procera for control of inflammation derived from Salmonella infections

BACKGROUND

Anti-inflammatory properties have been attributed to latex proteins of the medicinal plant Calotropis procera.

PURPOSE

A mixture of cysteine peptidases (LPp2) from C. procera latex was investigated for control of inflammatory mediators and inflammation in a mouse model of Salmonella infection.

METHODS

LPp2 peptidase activity was confirmed by the BANA assay. Cytotoxicity assays were conducted with immortalized macrophages. Peritoneal macrophages (pMØ) from Swiss mice were stimulated with lipopolysaccharide (LPS) in 96-well plates and then cultured with nontoxic concentrations of LPp2. Swiss mice intravenously received LPp2 (10 mg/kg) and then were challenged intraperitoneally with virulent Salmonella enterica Ser. Typhimurium.

RESULTS

LPp2 was not toxic at dosages lower than 62.2 μg/mL. LPp2 treatments of pMØ stimulated with LPS impaired mRNA expression of pro-inflammatory cytokines IL-1β, TNF-α, IL-6 and IL-10. LPp2 increased the intracellular bacterial killing in infected pMØ. Mice given LPp2 had a lower number of leukocytes in the peritoneal cavity in comparison to control groups 6 h after infection. The bacterial burden and histological damage were widespread in target organs of mice receiving LPp2.

CONCLUSION

We conclude that LPp2 contains peptidases with strong anti-inflammatory properties, which may render mice more susceptible to early disseminated infection caused by Salmonella.

ConBr lectin modulates MAPKs and Akt pathways and triggers autophagic glioma cell death by a mechanism dependent upon caspase-8 activation

Glioblastoma multiforme is the most aggressive type of glioma, with limited treatment and poor prognosis. Despite some advances over the last decade, validation of novel and selective antiglioma agents remains a challenge in clinical pharmacology. Prior studies have shown that leguminous lectins may exert various biological effects, including antitumor properties. Accordingly, this study aimed to evaluate the mechanisms underlying the antiglioma activity of ConBr, a lectin extracted from the Canavalia brasiliensis seeds. ConBr at lower concentrations inhibited C6 glioma cell migration while higher levels promoted cell death dependent upon carbohydrate recognition domain (CRD) structure. ConBr increased p38^MAPK and JNK and decreased ERK1/2 and Akt phosphorylation. Moreover, ConBr inhibited mTORC1 phosphorylation associated with accumulation of autophagic markers, such as acidic vacuoles and LC3 cleavage. Inhibition of early steps of autophagy with 3-methyl-adenine (3-MA) partially protected whereas the later autophagy inhibitor Chloroquine (CQ) had no protective effect upon ConBr cytotoxicity. ConBr also augmented caspase-3 activation without affecting mitochondrial function. Noteworthy, the caspase-8 inhibitor IETF-fmk attenuated ConBr induced autophagy and C6 glioma cell death. Finally, ConBr did not show cytotoxicity against primary astrocytes, suggesting a selective antiglioma activity. In summary, our results indicate that ConBr requires functional CRD lectin domain to exert antiglioma activity, and its cytotoxicity is associated with MAPKs and Akt pathways modulation and autophagy- and caspase-8- dependent cell death.

Schinus terebinthifolia leaf lectin (SteLL) has anti-infective action and modulates the response of Staphylococcus aureus-infected macrophages

Staphylococcus aureus is recognized as an important pathogen causing a wide spectrum of diseases. Here we examined the antimicrobial effects of the lectin isolated from leaves of Schinus terebinthifolia Raddi (SteLL) against S. aureus using in vitro assays and an infection model based on Galleria mellonella larvae. The actions of SteLL on mice macrophages and S. aureus-infected macrophages were also evaluated. SteLL at 16 µg/mL (8 × MIC) increased cell mass and DNA content of S. aureus in relation to untreated bacteria, suggesting that SteLL impairs cell division. Unlike ciprofloxacin, SteLL did not induce the expression of recA, crucial for DNA repair through SOS response. The antimicrobial action of SteLL was partially inhibited by 50 mM N-acetylglucosamine. SteLL reduced staphyloxathin production and increased ciprofloxacin activity towards S. aureus. This lectin also improved the survival of G. mellonella larvae infected with S. aureus. Furthermore, SteLL induced the release of cytokines (IL-6, IL-10, IL-17A, and TNF-α), nitric oxide and superoxide anion by macrophagens. The lectin improved the bactericidal action of macrophages towards S. aureus; while the expression of IL-17A and IFN-γ was downregulated in infected macrophages. These evidences suggest SteLL as important lead molecule in the development of anti-infective agents against S. aureus.

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

Edwardsiella piscicida Type III Secretion System Effector EseK Inhibits Mitogen-Activated Protein Kinase Phosphorylation and Promotes Bacterial Colonization in Zebrafish Larvae

Bacteria utilize type III secretion systems (T3SS) to deliver effectors directly into host cells. Hence, it is very important to identify the functions of bacterial (T3SS) effectors to understand host-pathogen interactions. Edwardsiella piscicida encodes a functional T3SS effector, EseK, which can be translocated into host cells and affect bacterial loads. Here, it was demonstrated that an eseK mutant (the ΔeseK mutant) significantly increased the phosphorylation levels of p38α, c-Jun NH₂-terminal kinases (JNK), and extracellular signal-regulated protein kinases 1/2 (ERK1/2) in HeLa cells. Overexpression of EseK directly inhibited mitogen-activated protein kinase (MAPK) signaling pathways in HEK293T cells. The ΔeseK mutant consistently promoted the phosphorylation of MAPKs in zebrafish larva infection models. Further, it was shown that the ΔeseK mutant increased the expression of tumor necrosis factor alpha (TNF-α) in an MAPK-dependent manner. Importantly, the EseK-mediated inhibition of MAPKs in vivo attenuated bacterial clearance in larvae. Taken together, this work reveals that the E. piscicida T3SS effector EseK promotes bacterial infection by inhibiting MAPK activation, which provides insights into the molecular pathogenesis of E. piscicida in fish.

Lectins as Promising Therapeutics for the Prevention and Treatment of HIV and Other Potential Coinfections

Human immunodeficiency virus-acquired immunodeficiency syndrome (HIV/AIDS) remains a global health problem. Current therapeutics specifically target the viral pathogen at various stages of its life cycle, although complex interactions between HIV and other pathogenic organisms are evident. Targeting HIV and concomitant infectious pathogens simultaneously, both by therapeutic regimens and in prevention strategies, would help contain the AIDS pandemic. Lectins, a ubiquitous group of proteins that specifically bind glycosylated molecules, are interesting compounds that could be used for this purpose, with demonstrated anti-HIV properties. In addition, potential coinfecting pathogens, including other enveloped viruses, bacteria, yeasts and fungi, and protozoa, display sugar-coated macromolecules on their surfaces, making them potential targets of lectins. This review summarizes the currently available findings suggesting that lectins should be further developed to simultaneously fight the AIDS pandemic and concomitant infections in HIV infected individuals.

Targeting the Immune System with Plant Lectins to Combat Microbial Infections

The arsenal of drugs available to treat infections caused by eukaryotic and prokaryotic microbes has been declining exponentially due to antimicrobial resistance phenomenon, leading to an urgent need to develop new therapeutic strategies. Host-directed immunotherapy has been reported as an attractive option to treat microbial infections. It consists in the improvement of host defenses by increasing the expression of inflammatory mediators and/or controlling of inflammation-induced tissue injury. Although the in vitro antimicrobial and immunomodulatory activities of lectins have been extensively demonstrated, few studies have evaluated their in vivo effects on experimental models of infections. This review aims to highlight the experimental use of immunomodulatory plant lectins to improve the host immune response against microbial infections. Lectins have been used in vivo both prophylactically and therapeutically resulting in the increased survival of mice under microbial challenge. Other studies successfully demonstrated that lectins could be used in combination with parasite antigens in order to induce a more efficient immunization. Therefore, these plant lectins represent new candidates for management of microbial infections. Furthermore, immunotherapeutic studies have improved our knowledge about the mechanisms involved in host–pathogen interactions, and may also help in the discovery of new drug targets.