The inhibition of Pseudomonas aeruginosa biofilm formation by micafungin and the enhancement of antimicrobial agent effectiveness in BALB/c mice

Micafungin inhibits biofilm formation by impeding 1,3-β-D-glucan synthesis in Candida albicans. Since Pseudomonas aeruginosa also has 1,3-β-D-glucan in its cell wall, this study assessed the effects of antibacterial agents in vitro and in vivo on micafungin-treated biofilm-forming P. aeruginosa isolates. After treatment with micafungin as well as with a panel of four antibacterial agents, biofilm production was significantly reduced as measured by spectrophotometry. The relative mRNA transcription levels for the genes encoding pellicles (pelC) and cell wall 1,3-β-D-glucan (ndvB), which were measured by quantitative reverse transcription PCR (qRT-PCR), significantly decreased with micafungin treatment. In vivo, the survival rates of P. aeruginosa-infected BALB/c mice significantly increased after combined treatment with micafungin and each of the antibacterial agents. Of these treatments, the combination of micafungin with levofloxacin had the highest survival rate; this combination was the most effective treatment against P. aeruginosa-induced infection.

Echinocandin antifungals: review and update

The echinocandins are a new and unique class of antifungal agents that act on the fungal cell wall by way of noncompetitive inhibition of the synthesis of 1,3-beta-glucans. All agents of this class are of parenteral formulation, with no oral preparations available. Caspofungin (Cancidas) was the first approved echinocandin, followed recently by micafungin (Mycamine) and anidulafungin (Eraxis). The precise role of the echinocandins in the antifungal armamentarium is still unfolding. Caspofungin is approved for the treatment of candidal esophagitis and candidemia, salvage therapy of Aspergillus infections and for empirical therapy of febrile neutropenia. Micafungin is likewise approved for candidal esophagitis, in addition to antifungal prophylaxis for hematopoietic stem cell transplant recipients. Anidulafungin is also approved for treatment of candidal esophagitis, as well as therapy of candidemia. There has been anecdotal use of these agents to treat less common fungal pathogens, as well as limited use as a component of combination antifungal therapy. The echinocandins are an important addition to the antifungal armamentarium in the treatment of fungal infections in both immunocompromised patients and those with normal immunity.

Protection by anti-beta-glucan antibodies is associated with restricted beta-1,3 glucan binding specificity and inhibition of fungal growth and adherence

Anti-β-glucan antibodies elicited by a laminarin-conjugate vaccine confer cross-protection to mice challenged with major fungal pathogens such as Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. To gain insights into protective β-glucan epitope(s) and protection mechanisms, we studied two anti-β-glucan monoclonal antibodies (mAb) with identical complementarity-determining regions but different isotypes (mAb 2G8, IgG2b and mAb 1E12, IgM). C. albicans, the most relevant fungal pathogen for humans, was used as a model.

Both mAbs bound to fungal cell surface and to the β1,3-β1,6 glucan of the fungal cell wall skeleton, as shown by immunofluorescence, electron-microscopy and ELISA. They were also equally unable to opsonize fungal cells in a J774 macrophage phagocytosis and killing assay. However, only the IgG2b conferred substantial protection against mucosal and systemic candidiasis in passive vaccination experiments in rodents. Competition ELISA and microarray analyses using sequence-defined glucan oligosaccharides showed that the protective IgG2b selectively bound to β1,3-linked (laminarin-like) glucose sequences whereas the non-protective IgM bound to β1,6- and β1,4-linked glucose sequences in addition to β1,3-linked ones. Only the protective IgG2b recognized heterogeneous, polydisperse high molecular weight cell wall and secretory components of the fungus, two of which were identified as the GPI-anchored cell wall proteins Als3 and Hyr1. In addition, only the IgG2b inhibited in vitro two critical virulence attributes of the fungus, hyphal growth and adherence to human epithelial cells.

Our study demonstrates that the isotype of anti-β-glucan antibodies may affect details of the β-glucan epitopes recognized, and this may be associated with a differing ability to inhibit virulence attributes of the fungus and confer protection in vivo. Our data also suggest that the anti-virulence properties of the IgG2b mAb may be linked to its capacity to recognize β-glucan epitope(s) on some cell wall components that exert critical functions in fungal cell wall structure and adherence to host cells.

Immunological actions of Sophy beta-glucan (beta-1,3-1,6 glucan), currently available commercially as a health food supplement

We examined the immunological actions of Sophy beta-glucan(Ikewaki N., et al. United States Patent 6956120 and Japan Patent 2004-329077), a type of beta-1,3-1,6 glucan produced by the black yeast Aureobasidium pullulans (A. pullulans) strain AFO-202, currently available commercially as a health food supplement, using different human in vitro experimental systems. Sophy beta-glucan significantly (P<0.01) stimulated the (3)H-thymidine incorporation rates (marker of DNA synthesis) in human peripheral blood mononuclear cells (PBMCs) obtained from normal adult donors, in vitro. Enzyme-linked immunoassays (EIAs) revealed that Sophy beta-glucan stimulated the production of interleukin-8 (IL-8) or soluble Fas (sFas), but not that of IL-1beta, IL-2, IL-6, IL-12 (p70+40), interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) or soluble Fas ligand (sFasL), in either cultured PBMCs or cells of the human monocyte-like cell line, U937. The induction by Sophy beta-glucan of DNA synthesis in PBMCs was completely blocked by the addition of monoclonal antibodies (mAbs) to CD11a, CD54, human leukocyte antigen-class II (HLA-class II), Toll-like receptor-2 (TLR-2), and Toll-like receptor-4 (TLR-4). In these blocking experiments using the mAbs, the main differences in the results between PBMCs and U937 cells were that the mAbs against TLR-2 and TLR-4 did not block the Sophy beta-glucan-induced production of IL-8 in the U937 cells. Furthermore, a mAb to the beta-glucan receptor, Dectin-1, significantly (P<0.05) blocked the Sophy beta-glucan induced DNA synthesis in the PBMCs, and Sophy beta-glucan-induced production of IL-8 in the U937 cells. The Sophy beta-glucan-induced production of IL-8 in the U937 cells was significantly (P<0.01) blocked by the conventional protein kinase C (PKC) inhibitor Go6976, the novel PKC inhibitor Rottlerin, the protein kinase A (PKA) inhibitor H-89, and the protein tyrosine kinase (PTK) inhibitor herbimycin A. Among these, the blocking effect of the novel PKC (PKC delta isoenzyme) inhibitor Rottlerin was the most pronounced. Studies employing reverse transcriptase-polymerase chain reaction (RT-PCR) showed that Sophy beta-glucan stimulated the expression of IL-8 mRNA in the U937 cells, and that this induction was inhibited by Rottlerin. Sophy beta-glucan also blocked the stimulator cell induction of DNA synthesis and IFN-gamma production in the responder cells in a one-way mixed lymphocyte reaction (MLR) using allogenic PBMCs. Interestingly, immunoglobulin G (IgG), but not IgM to Sophy beta-glucan was detected in the sera derived from normal adult donors and from the umbilical cord blood of neonates. Taken together, these findings strongly suggest that the Sophy beta-glucan may have unique immune regulatory or enhancing properties that could be exploited by the health food, medical and pharmaceutical industries.

Micafungin sodium, the second of the echinocandin class of antifungals: theory and practice

Micafungin is a new drug in the echinocandin class and is currently being investigated in Phase III clinical trials. Like other echinocandins, it inhibits 1,3-beta-D-glucan synthesis, thus achieving fungicidal activity against virtually all Candida spp., including those resistant to fluconazole, and fungistatic activity against Aspergillus spp. Micafungin sodium is available for intravenous administration only. It has a favorable safety and drug-drug interaction profile. Micafungin has been approved by the US FDA for treatment of esophageal candidiasis and for antifungal prophylaxis during the pre-engraftment phase in patients undergoing hematopoietic stem cell transplantation. Considering the competitive pricing as well as the good tolerability and efficacy, at present micafungin seems to be another choice for both of these indications. Current research has proven micafungin sodium to add a rational and effective option to the antifungal armamentarium, especially in esophageal candidiasis refractory to fluconazole treatment, in those intolerant to triazoles or in patients needing concomitant therapy interacting with triazoles. In addition to the current indications, recent uncontrolled clinical trials have demonstrated a marked success in the treatment of candidemia and invasive candidiasis. Results from in vitro studies, animal models, small clinical trials, as well as the obvious comparison with the more established caspofungin, hint at possible future indications such as invasive aspergillosis and empirical antifungal therapy. However, preclinical data on micafungin is inconsistent and published well-designed clinical studies are scarce. More controlled and sufficiently scaled trials are imperative in order to establish micafungin as a reliable and safe option in clinical practice.

Integrin engagement mediates the human polymorphonuclear leukocyte response to a fungal pathogen-associated molecular pattern

Extravasation of leukocytes from peripheral blood is required for an effective inflammatory response at sites of tissue infection. Integrins help mediate extravasation and navigate the leukocyte to the infectious source. A novel role for integrins in regulating the effector response to a cell wall component of fungal pathogens is the subject of the current study. Although phagocytosis is useful for clearance of unicellular fungi, the immune response against large, noningestible hyphae is not well-understood. Fungal beta-glucan, a pathogen-associated molecular pattern, activates production of superoxide anion in leukocytes without the need for phagocytosis. To model polymorphonuclear leukocyte (PMN) recognition of fungi under conditions in which phagocytosis cannot occur, beta-glucan was covalently immobilized onto tissue culture plastic. Plasma membrane-associated respiratory burst was measured by reduction of ferricytochrome C. Results show that the human PMN oxidative burst response to immobilized beta-glucan is suppressed by addition of beta(1) integrin ligands to the beta-glucan matrix. Suppression was dose dependent and steric hindrance was ruled out. beta(1) integrin ligands did not affect respiratory burst to ingestible beta-glucan-containing particles, phorbol esters or live yeast hyphae. Furthermore, in the absence of matrix, Ab activation of VLA3 or VLA5, but not other beta(1) integrins, also prevented beta-glucan-induced respiratory burst. beta(1)-induced suppression was blocked and burst response restored by treating neutrophils with either the cell-binding fragment of soluble human Fn, cyclic RGD peptide, or Ab specific to VLA3 or VLA5. Together these findings extend the functional role of beta(1) integrins to include modulating PMN respiratory burst to a pathogen-associated molecular pattern.

Blocking Effect of Anti-Dectin-1 Antibodies on the Anti-tumor Activity of 1,3-.BETA.-Glucan and the Binding of Dectin-1 to 1,3-.BETA.-Glucan

Schizophyllan (SPG) is used to treat cervical cancer in combination with irradiation to enhance the immunological surveillance system. Dectin-1 is a cell surface receptor for 1,3-beta-glucan. In this study, we prepared two anti-Dectin-1 monoclonal antibodies, 4B2 and SC30 having a K(D) of 7.04 x 10(-8) M and 1.55 x 10(-7) M, respectively, and evaluated the role of Dectin-1 in SPG-induced anti-tumor activity in mice. Expression of Dectin-1 on peritoneal macrophages and binding of SPG to the cells were decreased by administration of 4B2 and SC30. SPG-mediated anti-tumor activity was inhibited by 4B2 and SC30. 4B2 and SC30 inhibited the binding of SPG to splenocytes from mice. The binding of SPG-biotin to Dectin-1-transfected HEK293 cells was inhibited by 4B2, but not SC30. 4B2 and SC30 differ in their influence on Dectin-1 between primary cells and transduced cells, and Dectin-1 effects 1,3-beta-glucan-mediated anti-tumor activity in mice by binding to SPG.

Deletion of the CaBIG1 gene reduces beta-1,6-glucan synthesis, filamentation, adhesion, and virulence in Candida albicans

The human fungal pathogen Candida albicans is able to change its shape in response to various environmental signals. We analyzed the C. albicans BIG1 homolog, which might be involved in beta-1,6-glucan biosynthesis in Saccharomyces cerevisiae. C. albicans BIG1 is a functional homolog of an S. cerevisiae BIG1 gene, because the slow growth of an S. cerevisiae big1 mutant was restored by introduction of C. albicans BIG1. CaBig1p was expressed constitutively in both the yeast and hyphal forms. A specific localization of CaBig1p at the endoplasmic reticulum or plasma membrane similar to the subcellular localization of S. cerevisiae Big1p was observed in yeast form. The content of beta-1,6-glucan in the cell wall was decreased in the Cabig1Delta strain in comparison with the wild-type or reconstituted strain. The C. albicans BIG1 disruptant showed reduced filamentation on a solid agar medium and in a liquid medium. The Cabig1Delta mutant showed markedly attenuated virulence in a mouse model of systemic candidiasis. Adherence to human epithelial HeLa cells and fungal burden in kidneys of infected mice were reduced in the Cabig1Delta mutant. Deletion of CaBIG1 abolished hyphal growth and invasiveness in the kidneys of infected mice. Our results indicate that adhesion failure and morphological abnormality contribute to the attenuated virulence of the Cabig1Delta mutant.

Induction of human neutrophil chemotaxis by Candida albicans-derived -1,6-long glycoside side-chain-branched -glucan

Polysaccharide beta-1,3-D-glucans (beta-glucans) are components of the cell wall of various fungi and show immunomodulatory activities. beta-Glucans have been reported to enhance neutrophil accumulation during pathogenic fungi-induced lung inflammation. Therefore, we examined whether beta-glucans themselves possess chemotactic activities for human neutrophils. Among several kinds of beta-glucans, beta-1,6-long glucosyl side-chain-branched beta-glucan, isolated from Candida albicans [Candida soluble beta-D-glucan (CSBG)], dose-dependently induced neutrophil migration in a Boyden chamber system. In contrast, 1,6-monoglucosyl-branched beta-glucans, such as Sparassis crispa-derived beta-glucan (SCG) and grifolan (GRN), which were derived from nonpathogenic fungi, hardly induced neutrophil migration. Moreover, CSBG-induced neutrophil migration was inhibited completely by liposomes containing neutral glycosphingolipid lactosylceramide (LacCer; Galbeta1-4Glc-ceramide) but not NeuAcalpha2-3Galbeta1-4Glcbeta1-1'-Cer ganglioside. Furthermore, binding experiments demonstrated that CSBG bound to glycosphingolipids (such as LacCer) with a terminal galactose residue; however, SCG and GRN (1,6-monoglucosyl-branched beta-glucans) did not bind to LacCer. It is important that a Src kinase inhibitor protein phosphatase 1, a phosphatidylinositol-3 kinase (PI-3K) inhibitor wortmannin, and a Galpha(i/o) inhibitor pertussis toxin inhibited neutrophil migration toward CSBG. Taken together, our results suggest that beta-1,6-long glucosyl side-chain-branched beta-glucan CSBG binds to LacCer and induces neutrophil migration through the activation of Src family kinase/PI-3K/heterotrimeric G-protein signal transduction pathways.