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

Antivirulence activities of retinoic acids against Staphylococcus aureus

Multidrug-resistant bacteria such as Staphylococcus aureus constitute a global health problem. Gram-positive S. aureus secretes various toxins associated with its pathogenesis, and its biofilm formation plays an important role in antibiotic tolerance and virulence. Hence, we investigated if the metabolites of vitamin A1 might diminish S. aureus biofilm formation and toxin production. Of the three retinoic acids examined, 13-cis-retinoic acid at 10 μg/mL significantly decreased S. aureus biofilm formation without affecting its planktonic cell growth (MIC >400 μg/mL) and also inhibited biofilm formation by Staphylococcus epidermidis (MIC >400 μg/mL), but less affected biofilm formation by a uropathogenic Escherichia coli strain, a Vibrio strain, or a fungal Candida strain. Notably, 13-cis-retinoic acid and all-trans-retinoic acid significantly inhibited the hemolytic activity and staphyloxanthin production by S. aureus. Furthermore, transcriptional analysis disclosed that 13-cis-retinoic acid repressed the expressions of virulence- and biofilm-related genes, such as the two-component arlRS system, α-hemolysin hla, nuclease (nuc1 and nuc2), and psmα (phenol soluble modulins α) in S. aureus. In addition, plant and nematode toxicity assays showed that 13-cis-retinoic acid was only mildly toxic at concentrations many folds higher than its effective antibiofilm concentrations. These findings suggest that metabolites of vitamin A1, particularly 13-cis-retinoic acid, might be useful for suppressing biofilm formation and the virulence characteristics of S. aureus.

The lectin from Schinus terebinthifolia leaf (SteLL) reduces immobility of mice on the tail suspension test dependent on the monoaminergic and nitric oxide signaling

Depression underlies a common psychiatric disorder that has been rising in the diagnosis of long-term disabilities worldwide. Natural products have been studied as an antidepressant and anxiolytic agents aiming to make available new options for the daily basis treatment of those psychological disorders. SteLL is a lectin extracted from Schinus terebinthifolia leaf that has been revealed as an antimicrobial, immunomodulatory, antitumor, and antinociceptive agent. Nonetheless, the efficacy of SteLL in the treatment of depression has not yet been explored. In view of this, the aim of this study was to investigate the effect of SteLL in an acute protocol for symptoms of depression using the tail suspension test (TST) to assess despair. Administration of SteLL (1, 2 e 4 mg/kg) significantly diminished the immobility time of animals in the TST and this anti-immobility action was dependent on the carbohydrate-recognizing domain (CRD) since the prior incubation with casein (an inhibitor of SteLL carbohydrate-binding property) blocked the effect. SteLL effect was also reversed by pre-treatment with pharmacological antagonists of α2-adrenoceptor, 5-HT2A/2C serotonin receptor, and D1 dopamine receptor as well as by a selective inhibitor of iNOS (aminoguanidine). l-arginine, a precursor of NO, potentiated SteLL anti-immobility effect. In a subacute evaluation, the anti-immobility effect of SteLL persisted after seven days of treatment. Our findings suggest a role of SteLL in the modulation of depression mostly through monoaminergic and nitric oxide signaling.

Essential Oils of Aromatic Plant Species from the Atlantic Rainforest Exhibit Extensive Chemical Diversity and Antimicrobial Activity

Microbial resistance, caused by the overuse or inadequate application of antibiotics, is a worldwide crisis, increasing the risk of treatment failure and healthcare costs. Plant essential oils (EOs) consist of hydrophobic metabolites with antimicrobial activity. The antimicrobial potential of the chemical diversity of plants from the Atlantic Rainforest remains scarcely characterized. In the current work, we determined the metabolite profile of the EOs from aromatic plants from nine locations and accessed their antimicrobial and biocidal activity by agar diffusion assays, minimum inhibitory concentration, time-kill and cell-component leakage assays. The pharmacokinetic properties of the EO compounds were investigated by in silico tools. More than a hundred metabolites were identified, mainly consisting of sesqui and monoterpenes. Individual plants and botanical families exhibited extensive chemical variations in their EO composition. Probabilistic models demonstrated that qualitative and quantitative differences contribute to chemical diversity, depending on the botanical family. The EOs exhibited antimicrobial biocidal activity against pathogenic bacteria, fungi and multiple predicted pharmacological targets. Our results demonstrate the antimicrobial potential of EOs from rainforest plants, indicate novel macromolecular targets, and contribute to highlighting the chemical diversity of native species.

Plant Lectins: A Review on their Biotechnological Potential Toward Human Pathogens

The indiscriminate use of antibiotics is associated with the appearance of bacterial resistance. In light of this, plant-based products treating infections are considered potential alternatives. Lectins are a group of proteins widely distributed in nature, capable of reversibly binding carbohydrates. Lectins can bind to the surface of pathogens and cause damage to their structure, thus preventing host infection. The antimicrobial activity of plant lectins results from their interaction with carbohydrates present in the bacterial cell wall and fungal membrane. The data about lectins as modulating agents of antibiotic activity, potentiates the effect of antibiotics without triggering microbial resistance. In addition, lectins play an essential role in the defense against fungi, reducing their infectivity and pathogenicity. Little is known about the antiviral activity of plant lectins. However, their effectiveness against retroviruses and parainfluenza is reported in the literature. Some authors still consider mannose/ glucose/N-Acetylglucosamine binding lectins as potent antiviral agents against coronavirus, suggesting that these lectins may have inhibitory activity against SARS-CoV-2. Thus, it was found that plant lectins are an alternative for producing new antimicrobial drugs, but further studies still need to decipher some mechanisms of action.

Schinus terebinthifolius Leaf Lectin (SteLL) Reduces the Bacterial and Inflammatory Burden of Wounds Infected by Staphylococcus aureus Promoting Skin Repair

Staphylococcus aureus is commonly found in wound infections where this pathogen impairs skin repair. The lectin isolated from leaves of Schinus terebinthifolius (named SteLL) has antimicrobial and antivirulence action against S. aureus. This study evaluated the effects of topical administration of SteLL on mice wounds infected by S. aureus. Seventy-two C57/BL6 mice (6−8 weeks old) were allocated into four groups: (i) uninfected wounds; (ii) infected wounds, (iii) infected wounds treated with 32 µg/mL SteLL solution; (iv) infected wounds treated with 64 µg/mL SteLL solution. The excisional wounds (64 mm2) were induced on the dorsum and infected by S. aureus 432170 (4.0 × 106 CFU/wound). The daily treatment started 1-day post-infection (dpi). The topical application of both SteLL concentrations significantly accelerated the healing of S. aureus-infected wounds until the 7th dpi, when compared to untreated infected lesions (reductions of 1.95−4.55-fold and 1.79−2.90-fold for SteLL at 32 µg/mL and 64 µg/mL, respectively). The SteLL-based treatment also amended the severity of wound infection and reduced the bacterial load (12-fold to 72-fold for 32 µg/mL, and 14-fold to 282-fold for 64 µg/mL). SteLL-treated wounds show higher collagen deposition and restoration of skin structure than other groups. The bacterial load and the levels of inflammatory markers (IL-6, MCP-1, TNF-α, and VEGF) were also reduced by both SteLL concentrations. These results corroborate the reported anti-infective properties of SteLL, making this lectin a lead candidate for developing alternative agents for the treatment of S. aureus-infected skin lesions.

The Anxiolytic Activity of Schinus terebinthifolia Leaf Lectin (SteLL) Is Dependent on Monoaminergic Signaling although Independent of the Carbohydrate-Binding Domain of the Lectin

The potential of plant lectins (carbohydrate-binding proteins) for the treatment of neurological disorders such as anxiety and depression has started to be reported in the last few years. Schinus terebinthifolia leaves contain a lectin called SteLL, which has displayed antimicrobial, immunomodulatory, antitumor, and analgesic activities. However, the effects of SteLL on the Central Nervous System (CNS) have not yet been determined. In this study, we investigated the in vivo anxiolytic effect of SteLL in mice using the open field (OF) and elevated plus maze (EPM) tests. In the OF, SteLL (1, 2, and 4 mg/kg, i.p.) did not interfere with the number of crossings but significantly reduced the number of rearings. In the EPM, SteLL 4 mg/kg and the combination SteLL (1 mg/kg) plus diazepam (1 mg/kg) significantly increased the time spent in the open arms while reducing the time spent in the closed arms. The anxiolytic effect of SteLL did not seem to be dependent on the carbohydrate-binding domain of the lectin. Nevertheless, the SteLL effect in the EPM was reversed by the pretreatment with the pharmacological antagonists of the α2-adrenoceptor, 5-HT2A/2C serotonin receptor, and the D1 dopamine receptor. Overall, our results suggest that the anxiolytic effect of SteLL is dependent on the monoaminergic signaling cascade.

Plant Lectins as Potent Anti-coronaviruses, Anti-inflammatory, Antinociceptive and Antiulcer Agents

Lectins are defined as carbohydrate-binding proteins/glycoproteins of none immune origin, they are ubiquitous in nature, exist from bacteria to human cells. And due to their carbohydrate-binding recognition capacity, they have been a useful biological tool for the purification of glycoproteins and their subsequent characterization. Some plant lectins have also been revealed to own antinociceptive, antiulcer, and anti-inflammatory properties, where these features, in many instances, depending on the lectin carbohydrate-binding site. Coronavirus disease of 2019 (COVID-19) is a respiratory disease that struck the entire world leaving millions of people dead and more infected. Although COVID-19 vaccines have been made available, and quite a large number of world populations have already been immunized, the viral infection rates remained in acceleration, which continues to provoke major concern about the vaccines' efficacy. The belief in the ineffectiveness of the vaccine has been attributed in part to the recurrent mutations that occur in the epitope determinant fragments of the virus. Coronavirus envelope surface is extensively glycosylated being covered by more than sixty N-linked oligomannose, composite, and hybrid glycans with a core of Man3GlcNAc2Asn. In addition some O–linked glycans are also detected. Of these glyco-chains, many have also been exposed to several mutations, and a few remained conserved. Therefore, numerous plant lectins with a specificity directed towards these viral envelope sugars have been found to interact preferentially with them and are suggested to be scrutinized as a possible future tool to combat coronaviruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through blocking the viral attachment to the host cells. In this review, we will discuss the possible applications of plant lectins as anti-coronaviruses including SARS-CoV-2, antinociceptive, anti-inflammatory, and antiulcer agents with the proposed mechanism of their actions.

Staphyloxanthin as a Potential Novel Target for Deciphering Promising Anti-Staphylococcus aureus Agents

Staphylococcus aureus is a fatal Gram-positive pathogen threatening numerous cases of hospital-admitted patients worldwide. The emerging resistance of the pathogen to several antimicrobial agents has pressurized research to propose new strategies for combating antimicrobial resistance. Novel strategies include targeting the virulence factors of S. aureus. One of the most prominent virulence factors of S. aureus is its eponymous antioxidant pigment staphyloxanthin (STX), which is an auspicious target for anti-virulence therapy. This review provides an updated outline on STX and multiple strategies to attenuate this virulence factor. The approaches discussed in this article focus on bioprospective and chemically synthesized inhibitors of STX, inter-species communication and genetic manipulation. Various inhibitor molecules were found to exhibit appreciable inhibitory effect against STX and hence would be able to serve as potential anti-virulence agents for clinical use.

Quantum dots conjugated to lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL) as potential fluorescent nanotools for investigating Cryptococcus neoformans

This study reports the development of conjugates based on quantum dots (QD)s and lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL). Cryptococcus neoformans cells were chosen to evaluate the efficiency of the conjugates. Lectins were conjugated to QDs via adsorption, and the optical parameters (emission and absorption) were monitored. Lectin stability in the conjugates towards denaturing agents was investigated via fluorometry. The conjugation was evaluated using fluorescence microplate (FMA) and hemagglutination (HA) assays. The labeling of the C. neoformans cell surface was quantified using flow cytometry and observed via fluorescence microscopy. The QDs-SteLL and QDs-PgTeL conjugates, obtained at pH 7.0 and 8.0, respectively, showed the maintenance of colloidal and optical properties. FMA confirmed the conjugation, and the HA assay indicated that the lectin carbohydrate-binding ability was preserved after conjugation. SteLL and PgTeL showed stability towards high urea concentrations and heating. Conjugates labeled over 90% of C. neoformans cells as observed via flow cytometry and confirmed through fluorescence microscopy. C. neoformans labeling by conjugates was inhibited by glycoproteins, suggesting specific interactions through the lectin carbohydrate-binding site. Thus, an effective protocol for the conjugation of SteLL or PgTeL with QDs was proposed, yielding new nanoprobes useful for glycobiological studies.

Immunomodulatory and anti-infective effects of Cratylia mollis lectin (Cramoll) in a model of wound infection induced by Staphylococcus aureus

This work evaluated the immunomodulatory and anti-infective effects of Cratylia mollis lectin (Cramoll) in a model of wound infection induced by S. aureus. Swiss mice were divided into 3 groups (n = 12/group): non-inoculated (Control group); inoculated with S. aureus (Sa group); inoculated with S. aureus and treated with Cramoll (Sa + Cramoll group). In each animal, one lesion (64 mm²) was induced on the back and contaminated with S. aureus (~4.0 × 10⁶ CFU/wound). The treatment with Cramoll (5 μg/animal/day) started 1-day post-infection (dpi) and extended for 10 days. Clinical parameters (wound size, inflammatory aspects, etc.) were daily recorded; while cytokines levels, bacterial load and histological aspects were determined in the cutaneous tissue at 4^th dpi or 11^th dpi. The mice infected with S. aureus exhibited a delay in wound contraction and the highest inflammatory scores. These effects were impaired by the treatment with Cramoll which reduced the release of key inflammatory mediators (TNF-α, NO, VEGF) and the bacterial load at wound tissue. Histological evaluations showed a restauration of skin structures in the animals treated with Cramoll. Taken together, these results provide more insights about the healing and immunomodulatory properties of Cramoll and suggest this lectin as a lead compound for treatment of wound infection.

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.

Potential Application of Combined Therapy with Lectins as a Therapeutic Strategy for the Treatment of Bacterial Infections

Antibiotic monotherapy may become obsolete mainly due to the continuous emergence of resistance to available antimicrobials, which represents a major uncertainty to human health. Taking into account that natural products have been an inexhaustible source of new compounds with clinical application, lectins are certainly one of the most versatile groups of proteins used in biological processes, emerging as a promising alternative for therapy. The ability of lectins to recognize carbohydrates present on the cell surface allowed for the discovery of a wide range of activities. Currently the number of antimicrobials in research and development does not match the rate at which resistance mechanisms emerge to an effective antibiotic monotherapy. A promising therapeutic alternative is the combined therapy of antibiotics with lectins to enhance its spectrum of action, minimize adverse effects, and reduce resistance to treatments. Thus, this review provides an update on the experimental application of antibiotic therapies based on the synergic combination with lectins to treat infections specifically caused by multidrug-resistant and biofilm-producing Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We also briefly discuss current strategies involving the modulation of the gut microbiota, its implications for antimicrobial resistance, and highlight the potential of lectins to modulate the host immune response against oxidative stress.

Interplay between ESKAPE Pathogens and Immunity in Skin Infections: An Overview of the Major Determinants of Virulence and Antibiotic Resistance

The skin is the largest organ in the human body, acting as a physical and immunological barrier against pathogenic microorganisms. The cutaneous lesions constitute a gateway for microbial contamination that can lead to chronic wounds and other invasive infections. Chronic wounds are considered as serious public health problems due the related social, psychological and economic consequences. The group of bacteria known as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter sp.) are among the most prevalent bacteria in cutaneous infections. These pathogens have a high level of incidence in hospital environments and several strains present phenotypes of multidrug resistance. In this review, we discuss some important aspects of skin immunology and the involvement of ESKAPE in wound infections. First, we introduce some fundamental aspects of skin physiology and immunology related to cutaneous infections. Following this, the major virulence factors involved in colonization and tissue damage are highlighted, as well as the most frequently detected antimicrobial resistance genes. ESKAPE pathogens express several virulence determinants that overcome the skin's physical and immunological barriers, enabling them to cause severe wound infections. The high ability these bacteria to acquire resistance is alarming, particularly in the hospital settings where immunocompromised individuals are exposed to these pathogens. Knowledge about the virulence and resistance markers of these species is important in order to develop new strategies to detect and treat their associated infections.

Antinociceptive activity of Schinus terebinthifolia leaf lectin (SteLL) in sarcoma 180-bearing mice

ETHNOPHARMACOLOGY RELEVANCE

Schinus terebinthifolia Raddi leaves have been used in folk medicine due to several properties, including antitumor and analgesic effects. The variable efficacy and adverse effects of analgesic drugs have motivated the search for novel antinociceptive agents. It has been reported that the S. terebinthifolia leaf lectin (SteLL) has antitumor activity against sarcoma 180 in mice.

AIM OF THE STUDY

This work aimed to evaluate whether SteLL would reduce cancer pain using an orthotopic tumor model.

MATERIALS AND METHODS

A sarcoma 180 cell suspension was inoculated into the right hind paws of mice, and the treatments (150 mM NaCl, negative control; 10 mg/kg morphine, positive control; or SteLL at 1 and 2 mg/kg) were administered intraperitoneally 24 h after cell inoculation up to 14 days. Spontaneous nociception, mechanical hyperalgesia, and hot-plate tests were performed. Further, the volume and weight of the tumor-bearing paws were measured.

RESULTS

SteLL (2 mg/kg) improved limb use during ambulation. The lectin (1 and 2 mg/kg) also inhibited mechanical hyperalgesia and increased the latency time during the hot-plate test. Naloxone was found to reverse this effect, indicating the involvement of opioid receptors. The tumor-bearing paws of mice treated with SteLL exhibited lower volume and weight.

CONCLUSION

SteLL reduced hyperalgesia due to sarcoma 180 in the paws of mice, and this effect can be related to its antitumor action.