Laminarin, a soluble beta-glucan, inhibits macrophage phagocytosis of zymosan but has no effect on lipopolysaccharide mediated augmentation of phagocytosis

Human intestinal epithelial cells can internalize luminal fungi via LC3-associated phagocytosis

Background

Intestinal epithelial cells (IECs) are the first to encounter luminal microorganisms and actively participate in intestinal immunity. We reported that IECs express the β-glucan receptor Dectin-1, and respond to commensal fungi and β-glucans. In phagocytes, Dectin-1 mediates LC3-associated phagocytosis (LAP) utilizing autophagy components to process extracellular cargo. Dectin-1 can mediate phagocytosis of β-glucan-containing particles by non-phagocytic cells. We aimed to determine whether human IECs phagocytose β-glucan-containing fungal particles via LAP.

Methods

Colonic (n=18) and ileal (n=4) organoids from individuals undergoing bowel resection were grown as monolayers. Fluorescent-dye conjugated zymosan (β-glucan particle), heat-killed- and UV inactivated C. albicans were applied to differentiated organoids and to human IEC lines. Confocal microscopy was used for live imaging and immuno-fluorescence. Quantification of phagocytosis was carried out with a fluorescence plate-reader.

Results

zymosan and C. albicans particles were phagocytosed by monolayers of human colonic and ileal organoids and IEC lines. LAP was identified by LC3 and Rubicon recruitment to phagosomes and lysosomal processing of internalized particles was demonstrated by co-localization with lysosomal dyes and LAMP2. Phagocytosis was significantly diminished by blockade of Dectin-1, actin polymerization and NAPDH oxidases.

Conclusions

Our results show that human IECs sense luminal fungal particles and internalize them via LAP. This novel mechanism of luminal sampling suggests that IECs may contribute to the maintenance of mucosal tolerance towards commensal fungi.

Dialdehyde modification of laminarin for facile synthesis of ultrafine silver nanoparticles with excellent antibacterial and wound healing properties

Laminarin is a promising marine biopolymer that is abundant, non-toxic, and biodegradable. However, laminarin has a weak reduction potential for metal ions, resulting in the synthesis of a lower content of large-sized silver nanoparticles (AgNPs). Here, we showed that after the introduction of aldehyde groups, the reduction potential of laminarin increased, decreasing the synthesis time and increasing the density of AgNPs. ¹H NMR and FT-IR confirmed the addition of aldehyde groups on laminarin. The dialdehyde-modified laminarin (DLAM) showed in situ, simple, and rapid synthesis of ultrasmall-sized spherical AgNPs (<10 nm), as revealed by TEM images. The aldehyde and carboxyl groups of DLAM act as synchronized reducing and anchoring agents. The conversion of Ag ions into AgNPs-DLAM was confirmed by UV-Vis spectrophotometer, FTIR, XRD, and XPS analysis. The AgNPs-DLAM showed significantly enhanced antibacterial activities than silver ions against Escherichia coli and Staphylococcus aureus via causing morphological changes and pore formations in bacterial cells. The AgNPs-DLAM also inhibited bacterial biofilm formation. In contrast, the AgNPs-DLAM showed negligible toxicity toward human keratinocytes. Furthermore, AgNPs-DLAM increased the migration of human keratinocytes, indicating efficient wound healing properties. Thus, signifying the importance of AgNPs-DLAM in clinical applications.

Oral administration of botryosphaeran [(1 → 3)(1 → 6)-β-d-glucan] reduces inflammation through modulation of leukocytes and has limited effect on inflammatory nociception

Several biological activities of the fungal exopolysaccharide (1 → 3)(1 → 6)-β-d-glucan (botryosphaeran) have been described in the literature, but its effects on inflammation have not been evaluated. This study aimed to investigate the action of botryosphaeran on experimental mice models of carrageenan-induced acute pleurisy and acute paw edema, and complete Freund's adjuvant-induced persistent paw edema. All botryosphaeran doses tested (1.0, 2.5, 5.0, and 10.0 mg/kg birth weight [b.w.], orally administered) reduced leukocyte recruitment, nitric oxide (NO) levels, and protein extravasation in the pleural cavity. Botryosphaeran (5 mg/kg b.w.) did not diminish edema and mechanical hyperalgesia in the paw within 4 h; however, cold allodynia was alleviated within the first 2 h. In the persistent paw inflammation model, the effects of daily oral administration of botryosphaeran (5 mg/kg b.w.) were evaluated over 3 and 7 days. The fungal β-glucan significantly reduced the levels of the cytokines, tumor necrosis factor(TNF)-α, interleukin (IL)-6), and IL-10, in the paw homogenates in both protocols, while paw edema and the levels of advanced oxidation protein products (AOPP) only diminished on Day 7. No effect in mechanical hyperalgesia was observed. Oral treatment for 3 or 7 days also decreased the plasma levels of NO, AOPP, TNF-α, and IL-10. On Day 7, the number of leukocytes in the blood was also reduced by this treatment. Importantly, botryosphaeran did not induce inflammation in mice when administered alone over 7 days. This study demonstrated the anti-inflammatory and antinociceptive potential of botryosphaeran in these experimental models, making this fungal β-glucan a new possibility for complementary treating acute and chronic inflammation.

Protease-activated receptor 2 enhances innate and inflammatory mechanisms induced by lipopolysaccharide in macrophages from C57BL/6 mice

OBJECTIVE

This study was conducted to investigate the effects of the synthetic PAR2 agonist peptide (PAR2-AP) SLIGRL-NH₂ on LPS-induced inflammatory mechanisms in peritoneal macrophages.

METHODS

Peritoneal macrophages obtained from C57BL/6 mice were incubated with PAR2-AP and/or LPS, and the phagocytosis of zymosan fluorescein isothiocyanate (FITC) particles; nitric oxide (NO), reactive oxygen species (ROS), and cytokine production; and inducible NO synthase (iNOS) expression in macrophages co-cultured with PAR-2-AP/LPS were evaluated.

RESULTS

Co-incubation of macrophages with PAR2AP (30 µM)/LPS (100 ng/mL) enhanced LPS-induced phagocytosis; production of NO, ROS, and the pro-inflammatory cytokines interleukin (IL)-1β, tumour necrosis factor (TNF)-α, IL-6, and C-C motif chemokine ligand (CCL)2; and iNOS expression and impaired the release of the anti-inflammatory cytokine IL-10 after 4 h of co-stimulation. In addition, PAR2AP increased the LPS-induced translocation of the p65 subunit of the pro-inflammatory transcription factor nuclear factor kappa B (NF-κB) and reduced the expression of inhibitor of NF-κB.

CONCLUSION

This study provides evidence of a role for PAR2 in macrophage response triggered by LPS enhancing the phagocytic activity and NO, ROS, and cytokine production, resulting in the initial and adequate macrophage response required for their innate response mechanisms.

Protease-activated receptor 4 plays a role in lipopolysaccharide-induced inflammatory mechanisms in murine macrophages

The role of protease-activated receptor (PAR)4 in thrombin-induced platelet aggregation has been studied, and PAR4 blockade is thought to be useful as a new and promising approach in antiplatelet therapy in humans. In recent years, studies have been conducted to clarify the role of PAR4 in the host defense against invading microorganisms and pathogen-induced inflammation; however, to date, the role of PAR4 in mediating the LPS-induced inflammatory repertoire in macrophages remains to be elucidated. Here, we investigated the effects of the synthetic PAR4 agonist peptide (PAR4-AP) AYPGKF-NH₂ on the phagocytosis of zymosan-FITC particles; NO, ROS, and iNOS expression; and cytokine production in C57/BL6 macrophages cocultured with PAR4-AP/LPS. The PAR4-AP impaired LPS-induced and basal phagocytosis, which was restored by pharmacological PAR4 blockade. Coincubation with the PAR4-AP/LPS enhanced NO and ROS production and iNOS expression; decreased IL-10, but not TNF-α, in the culture supernatant; and increased translocation of the p65 subunit of the proinflammatory gene transcription factor NF-κ-B. Our results provide evidence for a complex mechanism and new approach by which PAR4 mediates the macrophage response triggered by LPS through counter-regulating the phagocytic activity of macrophages and innate response mechanisms implicated in the killing of invading pathogens.

Biomedical applications of laminarin

The ocean is par excellence a fertile territory of biodiversity on our planet. Marine-derived polysaccharides have been applied as functional materials in biomedicine due to their attractive bioactive properties, safety, high availability and low-cost production. Laminarin (or laminaran), a low molecular weight β-glucan storage polysaccharide present in brown algae, can be (bio-) chemically modified to enhance its biological activity and employed in cancer therapies, drug/gene delivery, tissue engineering, antioxidant and anti-inflammatory functions. This review provides a brief overview on laminarin characteristics, modification strategies and highlights its pivotal biomedical applications.

Overview of &#946;-Glucans from Laminaria spp.: Immunomodulation Properties and Applications on Biologic Models

Glucans are a group of glucose polymers that are found in bacteria, algae, fungi, and plants. While their properties are well known, their biochemical and solubility characteristics vary considerably, and glucans obtained from different sources can have different applications. Research has described the bioactivity of β-glucans extracted from the algae of the Laminaria genus, including in vivo and in vitro studies assessing pro- and anti-inflammatory cytokines, vaccine production, inhibition of cell proliferation, and anti- and pro-oxidant activity. Thus, the objective of this article was to review the potential application of β-glucans from Laminaria spp. in terms of their immunomodulatory properties, microorganism host interaction, anti-cancer activity and vaccine development.

Characterization of C-type lectins reveals an unexpectedly limited interaction between Cryptococcus neoformans spores and Dectin-1

Phagocytosis by innate immune cells is an important process for protection against multiple pathologies and is particularly important for resistance to infection. However, phagocytosis has also been implicated in the progression of some diseases, including the dissemination of the human fungal pathogen, Cryptococcus neoformans. Previously, we identified Dectin-1 as a likely phagocytic receptor for C. neoformans spores through the use of soluble components in receptor-ligand blocking experiments. In this study, we used gain-of-function and loss-of-function assays with intact cells to evaluate the in vivo role of Dectin-1 and other C-type lectins in interactions with C. neoformans spores and discovered stark differences in outcome when compared with previous assays. First, we found that non-phagocytic cells expressing Dectin-1 were unable to bind spores and that highly sensitive reporter cells expressing Dectin-1 were not stimulated by spores. Second, we determined that some phagocytes from Dectin-1^-/- mice interacted with spores differently than wild type (WT) cells, but the effects varied among assays and were modest overall. Third, while we detected small but statistically significant reductions in phagocytosis by primary alveolar macrophages from Dectin-1^-/- mice compared to WT, we found no differences in survival between WT and Dectin-1^-/- mice challenged with spores. Further analyses to assess the roles of other C-type lectins and their adapters revealed very weak stimulation of Dectin-2 reporter cells by spores and modest differences in binding and phagocytosis by Dectin-2^-/- bone marrow-derived phagocytes. There were no discernable defects in binding or phagocytosis by phagocytes lacking Mannose Receptor, Mincle, Card-9, or FcRγ. Taken together, these results lead to the conclusion that Dectin-1 and other C-type lectins do not individually play a major roles in phagocytosis and innate defense by phagocytes against C. neoformans spores and highlight challenges in using soluble receptor/ligand blocking experiments to recapitulate biologically relevant interactions.

Effects of Toll-like receptor ligands on RAW 264.7 macrophage morphology and zymosan phagocytosis

In this study we compared the effects of the Toll-like receptor (TLR) ligands lipopolysaccharide (LPS), flagellin, the synthetic bacterial triacylated lipopeptide Pam3-Cys-Ser-Lys4 (Pam3CSK4), Polyinosinic:polycytidylic acid (Poly I:C), and macrophage-activating lipopeptide (MALP-2), which are TLR4, TLR5, TLR1/2, TLR3, and TLR2/6 agonists, respectively, on cell morphology and phagocytosis of zymosan particles, derived from Saccharomyces cerevisiae, and rich in fungal PAMPs including beta-glucan, mannose, and chitin. LPS, Pam3CSK4, and MALP-2 induced an activated macrophage phenotype and enhanced zymosan phagocytosis. In contrast, flagellin and Poly I:C, respectively, had little effect on cell morphology and phagocytosis. We examined the role of scavenger receptor A (SR-A) on zymosan phagocytosis. Cells cultured in medium alone expressed SR-A, and LPS induced further expression of the receptor. We also observed inhibitory effects of scavenger receptor antagonists fucoidan, dextran sulphate, and Polyinosinic (Poly I), respectively, on zymosan phagocytosis of cells in medium alone and those pre-treated with LPS. We conclude that exposure to specific TLR ligands impacts both cellular morphology and phagocytic capacity, and that scavenger receptors contribute to zymosan ingestion as well as LPS-induced augmentation of phagocytosis.

Lipopolysaccharide-mediated enhancement of zymosan phagocytosis by RAW 264.7 macrophages is independent of opsonins, laminarin, mannan, and complement receptor 3

BACKGROUND

Fungal and bacterial coinfections are common in surgical settings; however, little is known about the effects of polymicrobial interactions on the cellular mechanisms involved in innate immune recognition and phagocytosis.

MATERIALS AND METHODS

Zymosan particles, cell wall derivatives of the yeast Saccharomyces cerevisiae, are used to model fungal interactions with host immune cells since they display carbohydrates, including beta-glucan, that are characteristic of fungal pathogens. Using in vitro cell culture, RAW 264.7 macrophages were challenged with zymosan, and phagocytosis determined via light microscopy. The effects of different concentrations of lipopolysaccharide (LPS) on zymosan phagocytosis were assessed. In addition, the transfer of supernatant from LPS-treated cells to naïve cells, the effects of soluble carbohydrates laminarin, mannan, or galactomannan, and the impact of complement receptor 3 (CR3) inhibition on phagocytosis were also determined.

RESULTS

LPS enhanced phagocytosis of zymosan in a dose-dependent manner. Transfer of supernatants from LPS-primed cells to naïve cells had no effect on phagocytosis. Laminarin inhibited zymosan phagocytosis in naïve cells but not in LPS-primed cells. Neither mannan, galactomannan, nor CR3 inhibition had a significant effect on ingestion of unopsonized zymosan in naïve or LPS-treated cells.

CONCLUSIONS

Zymosan recognition by naïve cells is inhibited by laminarin, but not mannan, galactomannan, or CR3 inhibition. LPS enhancement of phagocytosis is laminarin insensitive and not mediated by supernatant factors or zymosan engagement by the mannose or CR3 receptors. Our data suggest alternative mechanisms of zymosan recognition in the presence and absence of LPS.

Laminarin-induced apoptosis in human colon cancer LoVo cells

A number of scientific studies have revealed that laminarin has antitumor effects. Therefore, the aim of the present study was to investigate the apoptosis of LoVo cells and the underlying mechanisms induced by laminarin. LoVo cells were treated with various concentrations of laminarin and fluorescence-inverted microscopy was used to observe the morphology of LoVo cells treated with laminarin. In addition, western blotting was performed to analyze the expression levels of death receptor (DR)4, DR5, TNF-related apoptosis-inducing ligand (TRAIL), Fas-associated protein with death domain (FADD), caspase-8, caspase-3, Bid and tBid. Flow cytometry was conducted to analyze the expressions of Bcl-2 and Bax, and spectrophotometry was performed to quantify the activity of caspases-8, -3, -6 and -7. Following the treatment of LoVo cells with laminarin for 24 h, the expression levels of DR4, DR5, TRAIL, FADD, Bid, tBid and Bax were observed to be upregulated, whereas the expression levels of pro-caspase-8, pro-caspase-3 and Bcl-2 were downregulated. In addition, the activities of casapse-8, -3, -6 and -7 were observed to increase, which was a significant difference when compared with those of the control group. Therefore, laminarin is considered to induce the apoptosis of LoVo cells, which may occur via a DR pathway, suggesting that laminarin may be a potent agent for cancer treatment.

Immunomodulatory glycan lacto-N-fucopentaose III requires clathrin-mediated endocytosis to induce alternative activation of antigen-presenting cells

The mechanism of alternative activation of antigen-presenting cells (APCs) is largely unknown. Lacto-N-fucopentaose III (LNFPIII) is a biologically conserved pentasaccharide that contains the Lewis(x) trisaccharide. LNFPIII conjugates and schistosome egg antigens, which contain the Lewis(x) trisaccharide, drive alternative activation of APCs and induce anti-inflammatory responses in vivo, preventing inflammation-based diseases, including psoriasis, transplant organ rejection, and metabolic disease. In this study, we show that LNFPIII conjugates and schistosome egg antigens interact with APCs via a receptor-mediated process, requiring internalization of these molecules through a clathrin/dynamin-dependent but caveolus-independent endocytic pathway. Using inhibitors/small interfering RNA (siRNA) against dynamin and clathrin, we show for the first time that endocytosis of Lewis(x)-containing glycans is required to drive alternative maturation of antigen-presenting cells and Th2 immune responses. We identified mouse SIGNR-1 as a cell surface receptor for LNFPIII conjugates. Elimination of SIGNR-1 showed no effect on uptake of LNFPIII conjugates, suggesting that other receptors bind to and facilitate uptake of LNFPIII conjugates. We demonstrate that disruption of actin filaments partially prevented the entry of LNFPIII conjugates into APCs and that LNFPIII colocalizes with both early and late endosomal markers and follows the classical endosomal pathway leading to lysosome maturation. The results of this study show that the ability of LNFPIII to induce alternative activation utilizes a receptor-mediated process that requires a dynamin-dependent endocytosis. Thus, key steps have been defined in the previously unknown mechanism of alternative activation that ultimately leads to induction of anti-inflammatory responses.

Biodegradable microparticles covalently linked to surface antigens of the scuticociliate parasite P. dicentrarchi promote innate immune responses in vitro

The histiophagous scuticociliate endoparasite Philasterides dicentrarchi is an emerging pathogen that infects the turbot Scophthalmus maximus and thus causes important economic losses in turbot aquaculture. This in vitro study investigated the adjuvant capacity of biodegradable microspheres (MS) composed of two polymers (chitosan and Gantrez(®)) covalently coupled to surface antigens (Ag) of P. dicentrarchi. The coupled MS-Ag significantly stimulated the phagocytic response of both murine macrophages (RAW 264.7 cells) and leukocytes from the anterior kidney of turbot (HLK), at a level similar to that induced by zymosan A. The MS-Ag also significantly increased production of reactive oxygen and nitrogen species, as shown by the increased O(2) consumption and stimulation of the respiratory burst and nitric oxide production by murine and in particular by turbot HLK. The MS-Ag stimulated the production of the proinflammatory cytokine tumour necrosis factor alpha (TNFα) by murine and turbot HLK. The results confirm the high adjuvant capacity of biodegradable MS covalently bound to Ag as regards stimulating the innate immune response, and they justify the use of MS in the production of safe and effective vaccines against fish pathogens.

Laminarin induces apoptosis of human colon cancer LOVO cells through a mitochondrial pathway

Many scientific studies have shown that laminarin has anti-tumor effects, but the anti-tumor mechanism was unclear. The purpose of this study was to investigate the effect of laminarin on the induction of apoptosis in human colon cancer LOVO cells and the molecular mechanism involved. LOVO cells were treated with different concentrations of laminarin at different times. Morphology observations were performed to determine the effects of laminarin on apoptosis of LOVO cells. Flow cytometry (FCM) was used to detect the level of intracellular reactive oxygen species (ROS) and pH. Laser scanning confocal microscope (LSCM) was used to analyze intracellular calcium ion concentration, mitochondrion permeability transition pore (MPTP) and mitochondrial membrane potential (MMP). Western blotd were performed to analyze the expressions of Cyt-C, Caspase-9 and -3. The results showed the apoptosis morphology, which showed cell protuberance, concentrated cytoplasm and apoptotic bodies, was obvious after 72 h treatment. Laminarin treatment for 24 h increased the intracellular level of ROS and Ca²⁺; decreased pH value; activated intracellular MPTP and decreased MMP in dose-dependent manners. It also induced the release of Cyt-C and the activation of Caspase-9 and -3. In conclusion, laminarin induces LOVO cell apoptosis through a mitochondrial pathway, suggesting that it could be a potent agent for cancer prevention and treatment.