Reactivity of Limulus amoebocyte lysate towards (1----3)-beta-D-glucans

Comparison of two β-D-glucan assays for detecting invasive fungal diseases in immunocompromised patients

(1-3)-β-D-glucan (BDG) is a major biomarker of invasive fungal diseases (IFDs), which are life-threatening for immunodeficient patients. We compared the clinical performance of two BDG-detection assays. The precision, linearity, reference interval, and limit of quantitation of the Wako BDG assay were analyzed and the performance was compared with that of the Goldstream BDG assay using 272 clinical serum samples. The repeatability, within-laboratory imprecision, and limit of quantitation of the Wako BDG assay were 3.8%, 5.9%, and 7.35 pg/mL, respectively (linearity, 23.8-557 pg/mL; R² = 0.998). The correlation coefficient, slope, and y-intercept for the Wako BDG assay versus Goldstream BDG assay were 0.29, 3.82, and 0.04, respectively. The sensitivity and specificity were 43.8% and 94.9% for the Wako BDG assay and 39.6% and 83.5% for the Goldstream BDG assay, respectively. In clinical settings, the Wako BDG assay is suitable for diagnosing patients with IFDs.

[Fungal Beta-glucans: Structure and Effect on Host Immune Responses]

Fungi are eukaryotic microorganisms that show complex life cycles, including both anamorph and teleomorph stages. Beta-1,3-1,6-glucans (BGs) are major cell wall components in fungi. BGs are also found in a soluble form and are secreted by fungal cells. Studies of fungal BGs extensively expanded from 1960 to 1990 due to their applications in cancer immunotherapy. However, progress in this field slowed down due to the low efficacy of such therapies. In the early 21st century, the discovery of C-type lectin receptors significantly enhanced the molecular understanding of innate immunity. Moreover, pathogen-associated molecular patterns (PAMPs) and pattern recognition receptors (PRRs) were also discovered. Soon, dectin-1 was identified as the PRR of BGs, whereas BGs were established as PAMPs. Then, studies on fungal BGs focused on their participation in the development of deep-seated mycoses and on their role as a source of functional foods. Fungal BGs may have numerous and complex linkages, making it difficult to systematize them even at the primary structure level. Moreover, elucidating the structure of BGs is largely hindered by the multiplicity of genes involved in cell wall biosynthesis, including those for BGs, and by fungal diversity. The present review mainly focused on the characteristics of fungal BGs from the viewpoint of structure and immunological activities.

Triple-helix polysaccharides: Formation mechanisms and analytical methods

Triple helix conformation of polysaccharides is generally believed to be associated with their biological activities. However, the formation mechanisms and analytical methods for the triple helix polysaccharides, to our best knowledge, have not been systematically investigated. This article reviews specifically the literature on the formation and characterization of triple-helix polysaccharides. The formation mechanisms and related structural-conformation-bioactivity relationships are discussed; various analytical methods for characterizing triple-helix polysaccharides are summarized. This review devotes to a better understanding of the formation of polysaccharides based triple-helix structure and related analytical methods. These could provide some insights and inspirations for their applications in both food and pharmaceutical industries.

Possibility of Japanese Cedar Pollen Causing False Positives in the Deep Mycosis Test

Because Japanese cedar pollen (JCP) contains beta-1,3-d-glucan (BG), there is concern that its lingering presence in the atmosphere, especially during its scattering period, may cause false positives in the factor-G-based Limulus amebocyte lysate (LAL) assay used to test for deep mycosis (i.e., G-test). Hence, we examined whether the LAL assay would react positively with substances contained in JCP by using the G-test to measure JCP particles and extracts. BG was purified from the JCP extract on a BG-specific affinity column, and the percentage extractability was measured using three different BG-specific quantitative methods. The G-test detected 0.4 pg BG in a single JCP particle and 10 fg from a single particle in the extract. The percentage extractability of JCP-derived BG was not significantly different among the three quantitative methods. As the JCP particles should technically have been removed during serum separation, they should be less likely to be a direct false-positive factor. However, given that the LAL-assay-positive substances in the JCP extract were not distinguishable by the three BG-specific quantitative methods, we conclude that they may cause the background to rise. Therefore, in Japan false positives arising from JCP contamination should be considered when testing patients for deep mycosis.

N-Terminal (1→3)-β-d-Glucan Recognition Proteins from Insects Recognize the Difference in Ultra-Structures of (1→3)-β-d-Glucan

Recognition of (1→3)-β-d-glucans (BGs) by invertebrate β-1,3-d-glucan recognition protein (BGRP) plays a significant role in the activation of Toll pathway and prophenoloxidase systems in insect host defense against fungal invasion. To examine the structure diversity of BGRPs for the recognition of physiochemically different BGs, the binding specificity of BGRPs cloned from four different insects to structure different BGs was characterized using ELISA. Recombinant BGRPs expressed as Fc-fusion proteins of human IgG1 bound to the solid phase of BGs. Based on the binding specificities, the BGRPs were categorized into two groups with different ultrastructures and binding characters; one group specifically binds BGs with triple-helical conformation, while the other group recognizes BGs with disordered conformations like single-helical or partially opened triple helix. The BGRPs from the silkworm and the Indian meal moth bound to the BGs with a triple-helical structure, whereas BGRPs from the red flour beetle and yellow mealworm beetle showed no binding to triple-helical BGs, but bound to alkaline-treated BGs that have a partially opened triple-helical conformation. This evidence suggests that the insect BGRPs can distinguish between different conformations of BGs and are equipped for determining the diversity of BG structures.

Is Endotoxemia in Stable Hemodialysis Patients an Artefact? Limitations of the Limulus Amebocyte Lysate Assay and Role of (1→3)-β-D Glucan

Background

Elevated blood endotoxin levels are frequently reported in the dialysis population and are strongly linked with inflammation, a major predictor of mortality. Virtually all studies have employed the Limulus Amoebocyte Lysate (LAL) assay to detect endotoxin. However this assay is not endotoxin-specific and can be activated by (1→3)-β-glucan (BG), a component of fungal cell walls leading to false positive signals. Very few studies have taken account of this. We examined the influence of BG-based activation of the LAL assay on the detection of endotoxemia in this setting.

Method

We measured plasma endotoxin levels in 50 hemodialysis patients with and without the use of BG-blocking buffers. These buffers inhibit BG activation of the LAL assay to ensure that any signal detected is endotoxin-specific. Blood samples were measured for BG, interleukin-6 (IL-6), tumor necrosis factor-alfa (TNF-α) to examine the association between endotoxin signals, BG and inflammation.

Results

Endotoxin signals were detected in 50% of patients. On repeat measurement with a BG-blocking buffer, all detected endotoxin signals were extinguished. No patient had detectable endotoxemia. Plasma BG levels were significantly elevated in 58% of patients and were higher in those with detectable endotoxin signals using the LAL assay without BG-blocking buffers (78vs.54pg/mL;p<0.001). Endotoxin signal and BG levels did not correlate with levels of TNF-α or IL-6.

Conclusion

Use of the LAL assay for blood endotoxin detection in dialysis patients has its limitations due to high blood BG. Endotoxemia frequently reported in non-infected hemodialysis patients may be artefactual due to BG interference.

Natural and modified (1-->3)-beta-D-glucans in health promotion and disease alleviation

A number of polysaccharides with beta-glycosidic linkage are widespread in nature in a variety of sources. All have a common structure and the (1-->3)-beta-D-glucan backbone is essential. They have attracted attention over the years because of their bioactive and medicinal properties. In many cases their functional role is a mystery, in others it is well established. Because of their insoluble chemical nature, particulate (1-->3)-beta-D-glucans are not suitable for many medical applications. Various methods of changing or modifying the beta-D-glucan chemical structure and transforming it to a soluble form have been published. The beta-D-glucan bioactive properties can be affected positively or negatively by such modifications. This review examines beta-glucan sources in nature, health effects and structure-activity relationships. It presents the current state of beta-D-glucan solubilization methods and discusses their effectiveness and application possibilities for the future.

The solubilization and biological activities ofAspergillusβ-(1→3)-d-glucan

We have recently demonstrated that the cell wall beta-glucan of Candida albicans could be solubilized by sodium hypochlorite, followed by dimethylsulfoxide-extraction (NaClO-DMSO method). In this study, applying this method to Aspergillus spp., we prepared mycelial cell wall beta-glucan and examined its physical properties and immunotoxicological activity. The acetone-dried mycelia of Aspergillus spp. were oxidized by the NaClO-DMSO method. An analysis of (13)C NMR spectra revealed the preparations to be composed of alpha-(1 --> 3) and beta-(1 --> 3)-D-glucan. Also, the proportion of alpha-(1 --> 3) and beta-(1 --> 3)-D-glucan varied. Furthermore, a solubilized Aspergillus beta-glucan (ASBG) was prepared from OX-Asp by urea-autoclave treatment. ASBG showed limulus activity similar to Candida solubilized beta-glucan (CSBG), and there was little difference in the activity of ASBG between various Aspergillus spp. ASBG affected the production of IL-8 by human peripheral blood mononuclear cells (PBMC). ASBG should be useful for analyzing the clinical role of beta-glucan.

Activation of macrophages by linear (1right-arrow3)-beta-D-glucans. Impliations for the recognition of fungi by innate immunity

Although (1-->3)-beta-d-glucans, which are one of major fungal cell wall components, are known to activate invertebrate innate immune systems, their activities on mammalian cells remain elusive. Here, we report their activities on mouse macrophages. Among the various (1-->3)-beta-d-glucans, curdlan, a linear (1-->3)-beta-d-glucan, although not branched beta-glucans, exhibits significant activity to stimulate nuclear factor-kappaB in macrophages. The activity of curdlan is dramatically enhanced by pretreatment with sodium hydroxide or dimethyl sulfoxide, which disrupts multiple-stranded helices of (1-->3)-beta-d-glucans, and is dose-dependently inhibited by a (1-->3)-beta-d-glucan-binding protein and by laminarioligosaccharides with (1-->3)-beta-d-glucosidic linkages. Intriguingly, the activity of curdlan is also augmented by incubation with zymolyase, which releases (1-->3)-beta-d-glucans with a single helical structure from the glucan-networks assembled by multiple-stranded helices. The activation of macrophages culminates in the production of inducible nitric-oxide synthase, tumor necrosis factor-alpha, and macrophage inflammatory protein-2. Furthermore, a dominant-negative mutant of MyD88, an adaptor protein mediating signaling through the Toll-like receptor/inerleukin-1 receptor-like (TIR) domain, inhibits the activation of macrophages by curdlan. These results strongly suggest that macrophages respond to linear (1-->3)-beta-d-glucans, possibly released from fungal cell walls, via a receptor(s) harboring the TIR domain, such as a Toll-like receptor, to induce inflammatory reactions.

Th1/Th2-Balancing immunomodulating activity of gel-forming (1-->3)-beta-glucans from fungi

The immunomodulating effects of various gel-forming (1-->3)-beta-glucans, grifolan (GRN), SSG, sonifilan (SPG) and alkaline-treated SPG (SPG-OH), on balancing helper T cell activity were examined in a murine model. Plasma from mice that were injected with GRN or SPG-OH and trinitrophenyl ovalbumin (TNP-OVA) contained TNP-specific antibodies of both IgG1 and IgG2a isotypes. Administration of SSG and TNP-OVA significantly augmented the synthesis of IgG2a antibodies, while the synthesis of IgG1 was reduced. However, SPG did not enhance the antibody response. In the culture supernatants of splenocytes obtained from GRN- or SPG-OH-administered mice, high levels of IgGI and low levels of IgG2a and IFN gamma were detected. In contrast, high levels of IgG2a and IFN gamma and low levels of IgGI were detected in the case of administration of SSG. Furthermore, it was shown by intracellular cytokine staining that the proportion of IFN gamma+CD4+ double-positive cells among the CD4+ cells from mice administered SSG was most strongly increased by addition of PMA and A23187. On the other hand, the expression of IL-12 p40 mRNA was more markedly elevated in splenocytes after combined administration of TNP-OVA plus SSG than after administration of TNP-OVA alone. The highest IFN gamma production was observed when adherent cells of mice administered TNP-OVA and SSG were cultured with TNP-primed lymphocytes. This effect of administration of SSG on IFN-y production was completely inhibited by addition of anti-IL-12 mAb. In conclusion, our study showed that beta-glucans have various effects on the Th1 or Th2-dependent antibody subclasses, in particular, SSG induces the development of Th1 cells via the IL-12 pathway.

Measurement of blood clearance time by Limulus G test of Candida-water soluble polysaccharide fraction, CAWS, in mice

The Limulus G test, responsive to beta-1,3-D-glucan, is a well-established method for the detection of invasive fungal infection. We have recently found that Candida albicans released a water-soluble polysaccharide fraction (CAWS) into synthetic medium (Uchiyama et al., FEMS Immunol. Med. Microbiol. 24 (1999) 411-420). CAWS was composed of a mannoprotein-beta-glucan complex and activated Limulus factor G, and thus would be similar to the Limulus active substance in patient's blood. In a preliminary investigation, we have found that CAWS is lethal when administered intravenously in a murine system. In this study, we examined the toxicity and then the fate of CAWS in mice. The lethal toxicity was strain-dependent and strain DBA/2 was the most resistant. The toxicity was, at least in part, reduced by salbutamol sulfate and prednisolone treatment in the sensitive strains. On intravenous administration, the half clearance time (t1/2) was approximately 40 min in mice (DBA/2). On intraperitoneal administration, CAWS appeared in the blood with a peak concentration at 1 h. In order to establish a treatment plan, it is important to demonstrate the onset and the termination of deep-seated mycosis. The Limulus G test is suitable for the above purpose; however, it is necessary to fully understand the fate of beta-1,3-D-glucan in patients' blood.

Gel clot LAL assay in the initial management of peritoneal dialysis patients with peritonitis: a retrospective study

BACKGROUND

Indiscriminate use of broad-spectrum antibiotic treatment of peritonitis in peritoneal dialysis patients may have either unwanted side-effects or contribute to the development of antibiotic resistance. This may be avoided by improved diagnosis at presentation. The Limulus amoebocyte lysate assay is a convenient test detecting bacterial endotoxins or fungal beta glucans. This study evaluates a qualitative Limulus amoebocyte lysate test as a diagnostic tool used at presentation of a peritoneal dialysis patient with peritonitis.

METHODS

One-hundred and eleven episodes of peritonitis in peritoneal dialysis patients have been analysed retrospectively. Limulus amoebocyte lysate results at presentation were compared with culture results. A Limulus amoebocyte lysate assay was performed using a commercial kit by incubating a mixture of dialysate effluent and Limulus amoebocyte lysate reagent at 37 degrees C. The development of a stable solid clot was considered positive. The specificity and sensitivity of the test were calculated.

RESULTS

The specificity of the Limulus amoebocyte lysate assay was found to be 98% and the sensitivity 74%. Limulus amoebocyte lysate assay was false-negative in 13 cases of Gram-negative peritonitis (22%). Limulus amoebocyte lysate was positive in three of seven cases of fungal peritonitis. The study included one case each with false-positive Limulus amoebocyte lysate and with culture-negative peritonitis.

CONCLUSIONS

The Limulus amoebocyte lysate assay is a convenient and valuable diagnostic tool for excluding Gram-positive peritonitis in peritoneal dialysis patients. This allows more specific antibiotic treatment at presentation and may avoid the development of bacterial resistance. A negative Limulus amoebocyte lysate test is not reliable for the exclusion of Gram-negative peritonitis. In the absence of a positive culture result 48 h after presentation, accompanied by a delayed response to treatment, a positive Limulus amoebocyte lysate assay may indicate the presence of fungus. This justifies early empiric antifungal treatment before definitive culture results are made available. Routine Limulus amoebocyte lysate assay of dialysate effluent from continuous ambulatory peritoneal dialysis patients presenting with peritonitis is recommended.

Gradual solubilization of Candida cell wall beta-glucan by oxidative degradation in mice

Candida spp. is a medically important fungi which induces disseminated candidiasis and candidemia in hospitalized immunocompromised patients. The cell wall of Candida is mainly composed of two polysaccharides, mannan and beta-glucan, and at least part of beta-glucan is basically insoluble in H2O or NaOH. We became interested in when and how particulate beta-glucan changes to the soluble form. However, the fate of wall components has not been examined in detail. In this study, modification and solubilization of the cell wall beta-glucan were analyzed in vivo and in vitro. Cells of Candida, intravenously administered to mice (1 mg/mouse), were immediately deposited mainly in liver as determined by 3H-labeled cells. Beta-Glucans were detected in these mice for at least for 6 months by the beta-glucan specific assay. During this period, the insoluble cell wall beta-glucan was gradually solubilized in these organs, probably by oxidative stress of macrophages. Candida cells and particulate beta-glucans were also gradually solubilized in vitro using sodium hypochlorite solution, but part of the cell wall beta-glucan was still insoluble even after treatment with concentrated hypochlorite solution for one day at room temperature. These findings strongly suggested that the fungal cell wall beta-glucans were quite resistant to oxidative metabolism in vivo and in vitro, and thus deposited for quite long period in the host.

Kupffer cells play important roles in the metabolic degradation of a soluble anti-tumor (1-->3)-beta-D-glucan, SSG, in mice

Metabolic degradation of a soluble highly branched (-->3)-beta-D-glucan, SSG, was examined in mice using a macrophage blocker, gadolinium chloride (GdCl3). Intraperitoneally administered SSG distributed in the liver was slowly degraded, and after 5 weeks about 30% of the SSG became anionic. In addition, it is suggested that the metabolites would contain fewer branching points as assessed by the reactivity to limulus factor G. On the other hand, in the spleen, the molecular weight and the degree of branching of SSG were not changed for at least 5 weeks. Blockade of Kupffer cells by GdCl3 did not significantly change the distribution ratio of SSG in the liver. However, the treatment significantly delayed the degradation of SSG. These results suggested that Kupffer cells play important roles, not in the distribution, but in the oxidative degradation of SSG in the liver. In addition, splenic macrophages did not significantly contribute to the metabolic degradation of SSG.

Blood clearance of (1-->3)-beta-D-glucan in MRL lpr/lpr mice

(1-->3)-beta-D-Glucans have a variety of biological and immunopharmacological properties, and they are used clinically as biological response modifiers (BRMs). Clinically, these glucans have often been used for long periods by multiple dosing. During studies on the clearance and metabolism of the glucans in mice, we have found that, in the case of a single dose, the glucan was cleared from blood eventually, and remained constant in the organs for at least one month. Here, we investigated the clearance of glucans from the blood following multiple dosing using MRL lpr/lpr mice with an autoimmune disease. Two kinds of glucans, GRN from Grifola frondosa and SSG from Sclerotinia sclerotiorum, were administered to the mice once a week for more than 35 weeks (250 micrograms/week/mouse by the intraperitoneal route). Examination of the blood clearance of the glucans in these mice revealed that the glucan concentrations were always high (about 20 micrograms/ml for GRN and 200 micrograms/ml for SSG). It is also shown that the glucans were significantly deposited in the liver and spleen of these mice. These findings suggest that administration of a large quantity of the glucan saturated the reticuloendothelial system, resulting in circulation of the glucan in the blood.

Detection of (1-3)-beta-D-glucan in a rat model of aspergillosis

The G test containing factor G, fractioned from the Limulus lysate, was used to detect (1-3)-beta-D-glucan in a rat model of aspergillosis. Aspergillus fumigatus strain MF-13, 1 x 10(4) conidia, were inoculated transtracheally into rats treated with cortisone acetate (100 mg/kg) and fed a low-protein (8%) diet. Increased serum (1-3)-beta-D-glucan was found on the sixth day after inoculation in concentrations of 370 +/- 178 pg/ml (mean +/- SD) in untreated controls, and 154 +/- 43 pg/ml in rats treated with 0.5 mg/kg of amphotericin B. On day 11 (1-3)-beta-D-glucan concentrations were 2,590 +/- 2,940 pg/ml and 448 +/- 442 pg/ml, respectively. The elevation in levels of (1-3)-beta-D-glucan increased in correlation with the elevation of galactomannan antigen titers; (1-3)-beta-D-glucan is thus measurable during experimental aspergillosis in rats.

Structure-function relationships in microbial exopolysaccharides

Sufficient well-characterized microbial exopolysaccharides are now available to permit extensive studies on the relationship between their chemical structure and their physical attributes. This is seen even in homopolysaccharides with relatively simple structures but is more marked when greater differences in structure exist, as are found in several heteropolysaccharides. The specific and sometimes unique properties have, in the case of several of these polymers, provided a range of commercial applications. The existence of "families" of structurally related polysaccharides also indicates the specific role played by certain structures and substituents; the characteristics of several of these microbial polysaccharide families will be discussed here. Thus, microbial exopolysaccharides frequently carry acyl groups which may profoundly affect their interactive properties although these groups often have relatively little effect on solution viscosity. Xanthan with or without acylation shows marked differences in synergistic gelling with plant gluco- and galacto-mannans, although the polysaccharides with different acylation patterns show similar viscosity. Similarly "gelrite" from the bacterium originally designated as Auromonas (Pseudomonas)elodea is of greater potential value after deacetylation, when it provides a valuable gelling agent, than it is as a viscosifier in the natural acylated form. The Klebsiella type 54 polysaccharide only forms gels when it, too, has been chemically deacetylated to give a structure equivalent to the Enterobacter XM6 polymer. Both these polysaccharides form gels due to the enhanced interaction with cations following deacylation and to the conformation adopted after removal of the acyl groups. Recent work in our laboratory suggests that deacetylation of certain bacterial alginates also significantly increases ion binding by these polysaccharides, making them more similar in their properties to algal alginates even although the alginates from some Pseudomonas species lack poly-L-guluronic acid sequences. The existence within families of polysaccharides of types in which monosaccharides are altered within a specific structure, or with varying side-chains, also gives an indication of the way in which such substituents affect the physical properties of the polymers in aqueous solution.

Inhibition of high-molecular-weight-(1-->3)-beta-D-glucan-dependent activation of a limulus coagulation factor G by laminaran oligosaccharides and curdlan degradation products

Extensive surveys for the effects of various beta-D-glucans on the coagulation cascade in horseshoe crab amebocyte lysates showed that low-mol-wt-(1-->3)-beta-D-glucans and laminaran oligosaccharides inhibit the activation of a limulus coagulation factor G by high-mol-wt-(1-->3)-beta-D-glucans. The inhibitory properties are exclusively dependent upon their number-average mol wt (Mn) in a range of 342-58,100, which correspond to a degree of polymerization (dp) range of 2-359. The most effective is a laminaran dextrin of Mn 5800 (dp of 35-36), which causes 50% inhibition of factor G activation at a concentration of 3.16 ng/mL. The inhibition of the activation of factor G proportional to the concentration of the inhibitor, and the adsorption of factor G by inhibitory beta-D-glucan-conjugated cellulose suggested a high affinity of the inhibitory saccharides for the activator-recognition site of factor G. Branched (1-->6), (1-->3)-beta-D-glucans, laminarans, mixed linkage (1-->3), (1-->4)-beta-D-glucans, and partially substituted curdlan and laminaran were found to be inhibitory, possibly owing to clusters of consecutive (1-->3)-beta-D-glucopyranosyl residues as intrachain units. The inhibition appears to be related to the inability of the inhibitory (1-->3)-beta-D-glucans to form ordered conformations and to their tendency to take a random-coil structure in aqueous solution.

Sensitivity of Limulus amebocyte lysate (LAL) to LAL-reactive glucans

The sensitivity of Limulus amebocyte lysate (LAL) to LAL-reactive glucans (LRGs) and lipid A was tested by using commercially available and experimentally formulated LAL reagents. The glucans included two kinds of beta-(1,3)-D-glucans, laminarin and curdlan, and cellulosic material, LAL-reactive material (LAL-RM), extracted from a hollow-fiber (Cuprophan) hemodialyzer. LAL-RM loses its LAL activity when it is digested with cellulase and thus appears to be a beta-(1,4)-D-glucan or a mixed glucan containing a substantial proportion of beta-(1,4) linkages. All LAL reagents tested were at least 1,000-fold more sensitive to endotoxin than to LRGs. The presence of the surfactant Zwittergent was shown to interfere with reactivity to LRGs; LAL reagents without added Zwittergent reacted more strongly to LRGs than did the same reagents containing Zwittergent. Chloroform extraction of LAL increased the reagents' sensitivity to both endotoxin and LRGs, but it was not responsible for LRG reactivity. The addition of Zwittergent significantly reduced the sensitivity of LAL reagents to lipid A. LAL without the surfactant was equally sensitive to endotoxin and lipid A. Both curdlan and LAL-RM amplified or enhanced the LAL response to endotoxin. Kinetic turbidimetric studies demonstrated that the enhancement was dependent on the glucan concentration.