Curdlan stimulates tissue mast cells to synthesize pro-inflammatory mediators, generate ROS, and migrate via Dectin-1 receptor

Preparation of Single-Helical Curdlan Hydrogel and Its Activation with Coagulation Factor G

β-1,3-glucans are a kind of natural polysaccharide with immunomodulatory, antitumor, and anti-inflammatory properties. Curdlan, as the simplest linear β-1,3-glucan, possesses a variety of biological activities and thermogelation properties. However, due to the complexity and variability of the conformations of curdlan, the exact structure-activity relationship remains unclear. We prepare a chemically crosslinked curdlan hydrogel with the unique single-helical skeleton (named S gel) in 0.4 wt% NaOH at 40 °C, confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). X-ray diffractometry (XRD) data show that S gel maintains the single-helical crystal structure, and the degree of crystallinity of the S gel is ~24%, which is slightly lower than that of the raw powder (~31%). Scanning electron microscopy (SEM) reveals that S gel has a continuous network structure, with large pores measuring 50-200 μm, which is consistent with its high swelling property. Using the 13C high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) method, we determine that most of the single-helical skeleton carbon signals in the swollen S gel are visible, suggesting that the single-helical skeleton of S gel exhibits fascinating mobility at room temperature. Finally, we reveal that the binding of S gel to coagulation Factor G from tachypleus amebocyte lysate increases and saturates at 20 μL tachypleus amebocyte lysate per mg of S gel. Our prepared S gel can avoid the transformation of curdlan conformations and retain the bioactivity of binding to coagulation Factor G, making it a valuable material for use in the food industry and the pharmaceutical field. This work deepens the understanding of the relationship between the single-helical structure and the activity of curdlan, promoting the development and application of β-1,3-glucans.

Comparative analyses of various IgE-mediated and non-IgE-mediated inducers of mast cell degranulation for in vitro study

In vitro investigations of mast cell (MC) degranulation are essential for studying many diseases, particularly allergy and urticaria. Many MC-degranulation inducers are currently available. However, there is no previous systematic comparative analysis of these available inducers in term of their efficacies to induce MC degranulation. Herein, we performed systematic comparisons of efficacies of five well-known and commonly used MC-degranulation inducers. RBL-2H3 cells were sensitized with 50 ng/ml anti-DNP IgE or biotinylated IgE followed by stimulation with 100 ng/ml DNP-BSA or streptavidin, respectively. For non-IgE-mediated inducers, the cells were treated with 5 µg/ml substance P, compound 48/80, or A23187. At 15-, 30-, 45- and 60-min post-induction, several common MC-degranulation markers (including intracellular [Ca2+], β-hexosaminidase release, tryptase expression by immunofluorescence staining, cellular tryptase level by immunoblotting, secretory tryptase level by immunoblotting, CD63 expression by immunofluorescence staining, and CD63 expression by flow cytometry) were evaluated. The data showed that all these markers significantly increased after activation by all inducers. Among them, A23187 provided the greatest degrees of increases in intracellular [Ca2+] and β-hexosaminidase release at all time-points and upregulation of CD63 at one time-point. These data indicate that all these IgE-mediated (anti-DNP IgE/DNP-BSA and biotinylated IgE/streptavidin) and non-IgE-mediated (substance P, compound 48/80, and A23187) inducers effectively induce MC degranulation, while A23187 seems to be the most effective inducer for MC degranulation.

Galectin 3 enhances platelet aggregation and thrombosis via Dectin-1 activation: a translational study

AIMS

Galectin-3, a β-galactoside-binding lectin, is abnormally increased in cardiovascular disease. Plasma Galectin-3 receives a Class II recommendation for heart failure management and has been extensively studied for multiple cellular functions. The direct effects of Galectin-3 on platelet activation remain unclear. This study explores the direct effects of Galectin-3 on platelet activation and thrombosis.

METHODS AND RESULTS

A strong positive correlation between plasma Galectin-3 concentration and platelet aggregation or whole blood thrombus formation was observed in patients with coronary artery disease (CAD). Multiple platelet function studies demonstrated that Galectin-3 directly potentiated platelet activation and in vivo thrombosis. Mechanistic studies using the Dectin-1 inhibitor, laminarin, and Dectin-1-/- mice revealed that Galectin-3 bound to and activated Dectin-1, a receptor not previously reported in platelets, to phosphorylate spleen tyrosine kinase and thus increased Ca2+ influx, protein kinase C activation, and reactive oxygen species production to regulate platelet hyperreactivity. TD139, a Galectin-3 inhibitor in a Phase II clinical trial, concentration dependently suppressed Galectin-3-potentiated platelet activation and inhibited occlusive thrombosis without exacerbating haemorrhage in ApoE-/- mice, which spontaneously developed increased plasma Galectin-3 levels. TD139 also suppressed microvascular thrombosis to protect the heart from myocardial ischaemia-reperfusion injury in ApoE-/- mice.

CONCLUSION

Galectin-3 is a novel positive regulator of platelet hyperreactivity and thrombus formation in CAD. As TD139 has potent antithrombotic effects without bleeding risk, Galectin-3 inhibitors may have therapeutic advantages as potential antiplatelet drugs for patients with high plasma Galectin-3 levels.

Medical Use of Polycatecholamines + Oxidoreductases-Modified Curdlan Hydrogels-Perspectives

Curdlan (β-1,3-glucan), as a biodegradable polymer, is still an underestimated but potentially attractive matrix for the production of dressing materials. However, due to its lack of susceptibility to functionalization, its use is limited. The proposed curdlan modification, using a functional polycatecholamine layer, enables the immobilization of selected oxidoreductases (laccase and peroxidase) on curdlan hydrogel. The following significant changes of biological and mechanical properties of polycatecholamines + oxidoreductases-modified matrices were observed: reduced response of human monocytes in contact with the hydrogels, modulated reaction of human blood, in terms of hemolysis and clot formation, and changed mechanical properties. The lack of toxicity towards human fibroblasts and the suppression of cytokines released by human monocytes in comparison to pristine curdlan hydrogel, seems to make the application of such modifications attractive for biomedical purposes. The obtained results could also be useful for construction of a wide range of biomaterials based on other polymer hydrogels.

Candidalysin, a Virulence Factor of Candida albicans, Stimulates Mast Cells by Mediating Cross-Talk Between Signaling Pathways Activated by the Dectin-1 Receptor and MAPKs

PURPOSE

Although mast cells (MCs) modulate the activity of effector cells during Candida albicans infection, their role in the pathogenesis of candidiasis remains unclear. Candidalysin, a C. albicans-derived peptide toxin, is a crucial factor in fungal infections. We aimed to investigate the effect of candidalysin on MC activation and the underlying molecular mechanism.

METHODS

Serum from candidalysin-immunized mice was used to measure candidalysin expression in patients infected with C. albicans. MC degranulation and migration were evaluated by β-hexosaminidase release assay and chemotaxis assay, respectively. EIA and ELISA were used to evaluate the production of eicosanoids and cytokines/chemokines, respectively. The production of nitric oxide (NO) was measured with a DAF-FM diacetate kit, while reactive oxygen species (ROS) production was analyzed by flow cytometry. MAPK activation was evaluated by Western blotting.

RESULTS

We detected high candidalysin expression in the lesions of patients infected with C. albicans, and the MC number was increased in these lesions. LL-37 colocalized with MCs in the lesions of candidiasis patients. Candidalysin-enhanced MC accumulation in mice and treating LAD2 and HMC-1 cells with candidalysin induced their degranulation, migration, and production of pro- and anti-inflammatory cytokines/chemokines, eicosanoids, ROS, NO, and LL-37. Interestingly, C. albicans strains lacking candidalysin failed to induce MC activation. Moreover, candidalysin increased dectin-1 expression, and the inhibition of dectin-1 decreased MC activation. Downstream dectin-1 signaling involved the MAPK pathways.

CONCLUSION

The finding that candidalysin causes cutaneous MC activation may improve our understanding of the role of MCs in the pathology of cutaneous C. albicans infection.

More Prominent Inflammatory Response to Pachyman than to Whole-Glucan Particle and Oat-β-Glucans in Dextran Sulfate-Induced Mucositis Mice and Mouse Injection through Proinflammatory Macrophages

(1→3)-β-D-glucans (BG) (the glucose polymers) are recognized as pathogen motifs, and different forms of BGs are reported to have various effects. Here, different BGs, including Pachyman (BG with very few (1→6)-linkages), whole-glucan particles (BG with many (1→6)-glycosidic bonds), and Oat-BG (BG with (1→4)-linkages), were tested. In comparison with dextran sulfate solution (DSS) alone in mice, DSS with each of these BGs did not alter the weight loss, stool consistency, colon injury (histology and cytokines), endotoxemia, serum BG, and fecal microbiome but Pachyman-DSS-treated mice demonstrated the highest serum cytokine elicitation (TNF-α and IL-6). Likewise, a tail vein injection of Pachyman together with intraperitoneal lipopolysaccharide (LPS) induced the highest levels of these cytokines at 3 h post-injection than LPS alone or LPS with other BGs. With bone marrow-derived macrophages, BG induced only TNF-α (most prominent with Pachyman), while LPS with BG additively increased several cytokines (TNF-α, IL-6, and IL-10); inflammatory genes (iNOS, IL-1β, Syk, and NF-κB); and cell energy alterations (extracellular flux analysis). In conclusion, Pachyman induced the highest LPS proinflammatory synergistic effect on macrophages, followed by WGP, possibly through Syk-associated interactions between the Dectin-1 and TLR-4 signal transduction pathways. Selection of the proper form of BGs for specific clinical conditions might be beneficial.

Do Mast Cells Contribute to the Antifungal Host Defense?

The fungal kingdom includes a group of microorganisms that are widely distributed in the environment, and therefore the exposure to them is almost constant. Furthermore, fungal components of the microbiome, i.e., mycobiome, could serve as a reservoir of potentially opportunistic pathogens. Despite close encounters with fungi, defense mechanisms that develop during fungal infections remain unexplored. The strategic location of mast cells (MCs) close to the external environment places them among the first cells to encounter pathogens along with the other innate immune cells. MCs are directly involved in the host defense through the ability to destroy pathogens or indirectly by activating other immune cells. Most available data present MCs’ involvement in antibacterial, antiviral, or antiparasitic defense mechanisms. However, less is known about their contribution in defense mechanisms against fungi. MCs may support immune responses to fungi or their specific molecules through initiated degranulation, synthesis and release of cytokines, chemokines, mediators, and generation of reactive oxygen species (ROS), as well as immune cells’ recruitment, phagocytosis, or provision of extracellular DNA traps. This review summarizes current knowledge on host defense mechanisms against fungi and MCs’ involvement in those processes. It also describes the effects of fungi or fungus-derived constituents on MCs’ activity.

Mast cell phenotypic plasticity and their activity under the influence of cathelicidin-related antimicrobial peptide (CRAMP) and IL-33 alarmins

Invading pathogens are contained/eliminated by orchestrated actions of different humoral components of the innate immune response. One of them is endogenous molecules called alarmins, which contribute to diverse processes from danger sense until the infection extinction. Considering the participation of mast cells (MCs) in many aspects of the body's defense and, on the other hand, the importance of alarmins as molecules that signal damage/danger, in this study, we evaluated the effect of alarmins on MC phenotype and activity. We found that cathelicidin CRAMP and cytokine IL-33 significantly affect the appearance of Dectin-1, Dectin-2, RIG-I, and NOD1 receptors in mature MCs and modulate their inflammatory response. We established that chosen alarmins might stimulate MCs to release pro-inflammatory and immunoregulatory mediators and induce a migratory response. In conclusion, our data highlight that alarmins CRAMP and IL-33 might strongly influence MC features and activity, mainly by strengthening their role in the inflammatory mechanisms and controlling the activity of cells participating in antimicrobial processes.

Mannan activates tissue native and IgE-sensitized mast cells to proinflammatory response and chemotaxis in TLR4-dependent manner

Mast cells take part in host defense against microorganisms as they are numerous at the portal of infection, exert several essential mechanisms of pathogen destruction, and they express pattern recognition receptors. Accumulating evidence indicates that these cells are involved in the control and clearance of bacterial, viral, or parasitic infections, but much less is known about their contribution in defense against fungi. The study was aimed to establish whether mannan, which comprises an outermost layer and major structural constituent of the fungal cell wall, may directly stimulate tissue mast cells to the antifungal response. Our findings indicate that mannan activates mast cells isolated from the rat peritoneal cavity to initiate the proinflammatory response. We found that mannan stimulates mast cells to release histamine and to generate cysteinyl leukotrienes, cytokines (IFN-γ, GM-CSF, TNF), and chemokines (CCL2, CCL3). It also increased the mRNA expression of various cytokines/chemokines. We also documented that mannan strongly activates mast cells to generate reactive oxygen species and serves as a potent chemoattractant for these cells. Furthermore, we established that mannan-induced activity of mast cells is mediated via TLR4 with the involvement of the spleen tyrosine kinase molecule. Taking together, our results clearly support the idea that mast cells act as sentinel cells and crucially determine the course of the immune response during fungal infection. Additionally, presented data on IgE-coated mast cells suggest that exposure to fungal mannan could influence the severity of IgE-dependent diseases, including allergic ones.

Comparative Study on Curcumin Loaded in Golden Pompano (Trachinotus blochii) Head Phospholipid and Soybean Lecithin Liposomes: Preparation, Characteristics and Anti-Inflammatory Properties

In this study, we compared the characteristics and in vitro anti-inflammatory effects of two curcumin liposomes, prepared with golden pompano head phospholipids (GPL) and soybean lecithin (SPC). GPL liposomes (GPL-lipo) and SPC liposomes (SPC-lipo) loaded with curcumin (CUR) were prepared by thin film extrusion, and the differences in particle size, ζ-potential, morphology, and storage stability were investigated. The results show that GPL-lipo and SPC-lipo were monolayer liposomes with a relatively small particle size and excellent encapsulation rates. However, GPL-lipo displayed a larger negative ζ-potential and better storage stability compared to SPC-lipo. Subsequently, the effects of phospholipids in regulating the inflammatory response of macrophages were evaluated in vitro, based on the synergistic effect with CUR. The results showed that both GPL and SPC exerted excellent synergistic effect with CUR in inhibiting the lipopolysaccharide (LPS)-induced secretion of nitric oxide (NO), reactive oxygen species (ROS), and pro-inflammatory genes (tumor necrosis factor (TNF)-α, interleukin 1β (IL-β), and interleukin 6 (IL-6)) in RAW264.7 cells. Interestingly, GPL-lipo displayed superior inhibitory effects, compared to SPC-lipo. The findings provide a new innovative bioactive carrier for development of stable CUR liposomes with good functional properties.

Native and IgE-primed rat peritoneal mast cells exert pro-inflammatory activity and migrate in response to yeast zymosan upon Dectin-1 engagement

Mast cells (MCs) play an essential role in host defense, primarily because of their location, their ability to pathogen destruction via several mechanisms, and the pattern recognition receptors they express. Even though most data is available regarding MC activation by various bacteria- or virus-derived molecules, those cells' activity in response to constituents associated with fungi is not recognized enough. Our research aimed to address whether Saccharomyces cerevisiae-derived zymosan, i.e., β-(1,3)-glucan containing mannan particles, impacts MC activity aspects. Overall, the obtained results indicate that zymosan has the potential to elicit a pro-inflammatory response of rat peritoneal MCs. For the first time ever, we provided evidence that zymosan induces fully mature MC migration, even in the absence of extracellular matrix (ECM) proteins. Moreover, the zymosan-induced migratory response of MCs is almost entirely a result of directional migration, i.e., chemotaxis. We found that zymosan stimulates MCs to degranulate and generate lipid mediators (cysLTs), cytokines (IFN-α, IFN-β, IFN-γ, GM-CSF, TNF), and chemokine (CCL2). Zymosan also upregulated mRNA transcripts for several cytokines/chemokines with pro-inflammatory/immunoregulatory activity. Moreover, we documented that zymosan activates MCs to produce reactive oxygen species (ROS). Lastly, we established that the zymosan-induced MC response is mediated through activation of the Dectin-1 receptor. In general, our results strongly support the notion that MCs contribute to innate antifungal immunity and bring us closer to elucidate their role in host-pathogenic fungi interactions. Besides, provided findings on IgE-sensitized MCs appear to indicate that exposure to fungal zymosan could affect the severity of IgE-dependent disorders, including allergic ones.

Understanding Pseudomonas aeruginosa-Host Interactions: The Ongoing Quest for an Efficacious Vaccine

Pseudomonas aeruginosa is a leading cause of chronic respiratory infections in people with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD), and acute infections in immunocompromised individuals. The adaptability of this opportunistic pathogen has hampered the development of antimicrobial therapies, and consequently, it remains a major threat to public health. Due to its antimicrobial resistance, vaccines represent an alternative strategy to tackle the pathogen, yet despite over 50 years of research on anti-Pseudomonas vaccines, no vaccine has been licensed. Nevertheless, there have been many advances in this field, including a better understanding of the host immune response and the biology of P. aeruginosa. Multiple antigens and adjuvants have been investigated with varying results. Although the most effective protective response remains to be established, it is clear that a polarised Th2 response is sub-optimal, and a mixed Th1/Th2 or Th1/Th17 response appears beneficial. This comprehensive review collates the current understanding of the complexities of P. aeruginosa-host interactions and its implication in vaccine design, with a view to understanding the current state of Pseudomonal vaccine development and the direction of future efforts. It highlights the importance of the incorporation of appropriate adjuvants to the protective antigen to yield optimal protection.