Exploiting Mannuronan C-5 Epimerases in Commercial Alginate Production.

Alginates are one of the major polysaccharide constituents of marine brown algae in commercial manufacturing. However, the content and composition of alginates differ according to the distinct parts of these macroalgae and have a direct impact on the concentration of guluronate and subsequent commercial value of the final product. The Azotobacter vinelandii mannuronan C-5 epimerases AlgE1 and AlgE4 were used to determine their potential value in tailoring the production of high guluronate low-molecular-weight alginates from two sources of high mannuronic acid alginates, the naturally occurring harvested brown algae (Ascophyllum nodosum, Durvillea potatorum, Laminaria hyperborea and Lessonia nigrescens) and a pure mannuronic acid alginate derived from fermented production of the mutant strain of Pseudomonas fluorescens NCIMB 10,525. The mannuronan C-5 epimerases used in this study increased the content of guluronate from 32% up to 81% in both the harvested seaweed and bacterial fermented alginate sources. The guluronate-rich alginate oligomers subsequently derived from these two different sources showed structural identity as determined by proton nuclear magnetic resonance (1H NMR), high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and size-exclusion chromatography with online multi-angle static laser light scattering (SEC-MALS). Functional identity was determined by minimum inhibitory concentration (MIC) assays with selected bacteria and antibiotics using the previously documented low-molecular-weight guluronate enriched alginate OligoG CF-5/20 as a comparator. The alginates produced using either source showed similar antibiotic potentiation effects to the drug candidate OligoG CF-5/20 currently in development as a mucolytic and anti-biofilm agent. These findings clearly illustrate the value of using epimerases to provide an alternative production route for novel low-molecular-weight alginates.

Cellulose Nanofibril Formulations Incorporating a Low-Molecular-Weight Alginate Oligosaccharide Modify Bacterial Biofilm Development.

Cellulose nanofibrils (CNFs) from wood pulp are a renewable material possessing advantages for biomedical applications because of their customizable porosity, mechanical strength, translucency, and environmental biodegradability. Here, we investigated the growth of multispecies wound biofilms on CNF formulated as aerogels and films incorporating the low-molecular-weight alginate oligosaccharide OligoG CF-5/20 to evaluate their structural and antimicrobial properties. Overnight microbial cultures were adjusted to 2.8 × 109 colony-forming units (cfu) mL-1 in Mueller Hinton broth and growth rates of Pseudomonas aeruginosa PAO1 and Staphylococcus aureus 1061A monitored for 24 h in CNF dispersions sterilized by γ-irradiation. Two CNF formulations were prepared (20 g m-2) with CNF as air-dried films or freeze-dried aerogels, with or without incorporation of an antimicrobial alginate oligosaccharide (OligoG CF-5/20) as a surface coating or bionanocomposite, respectively. The materials were structurally characterized by scanning electron microscopy (SEM) and laser profilometry (LP). The antimicrobial properties of the formulations were assessed using single- and mixed-species biofilms grown on the materials and analyzed using LIVE/DEAD staining with confocal laser scanning microscopy (CLSM) and COMSTAT software. OligoG-CNF suspensions significantly decreased the growth of both bacterial strains at OligoG concentrations >2.58% (P < 0.05). SEM showed that aerogel-OligoG bionanocomposite formulations had a more open three-dimensional structure, whereas LP showed that film formulations coated with OligoG were significantly smoother than untreated films or films incorporating PEG400 as a plasticizer (P < 0.05). CLSM of biofilms grown on films incorporating OligoG demonstrated altered biofilm architecture, with reduced biomass and decreased cell viability. The OligoG-CNF formulations as aerogels or films both inhibited pyocyanin production (P < 0.05). These novel CNF formulations or bionanocomposites were able to modify bacterial growth, biofilm development, and virulence factor production in vitro. These data support the potential of OligoG and CNF bionanocomposites for use in biomedical applications where prevention of infection or biofilm growth is required.

Alginate Oligosaccharide-Induced Modification of the lasI-lasR and rhlI-rhlR Quorum-Sensing Systems in Pseudomonas aeruginosa.

Pseudomonas aeruginosa plays a major role in many chronic infections. Its ability to readily form biofilms contributes to its success as an opportunistic pathogen and its resistance/tolerance to antimicrobial/antibiotic therapy. A low-molecular-weight alginate oligomer (OligoG CF-5/20) derived from marine algae has previously been shown to impair motility in P. aeruginosa biofilms and disrupt pseudomonal biofilm assembly. As these bacterial phenotypes are regulated by quorum sensing (QS), we hypothesized that OligoG CF-5/20 may induce alterations in QS signaling in P. aeruginosa QS regulation was studied by using Chromobacterium violaceum CV026 biosensor assays that showed a significant reduction in acyl homoserine lactone (AHL) production following OligoG CF-5/20 treatment (≥2%; P < 0.05). This effect was confirmed by liquid chromatography-mass spectrometry analysis of C4-AHL and 3-oxo-C12-AHL production (≥2%; P < 0.05). Moreover, quantitative PCR showed that reduced expression of both the las and rhl systems was induced following 24 h of treatment with OligoG CF-5/20 (≥0.2%; P < 0.05). Circular dichroism spectroscopy indicated that these alterations were not due to steric interaction between the AHL and OligoG CF-5/20. Confocal laser scanning microscopy (CLSM) and COMSTAT image analysis demonstrated that OligoG CF-5/20-treated biofilms had a dose-dependent decrease in biomass that was associated with inhibition of extracellular DNA synthesis (≥0.5%; P < 0.05). These changes correlated with alterations in the extracellular production of the pseudomonal virulence factors pyocyanin, rhamnolipids, elastase, and total protease (P < 0.05). The ability of OligoG CF-5/20 to modify QS signaling in P. aeruginosa PAO1 may influence critical downstream functions such as virulence factor production and biofilm formation.

A Low-Molecular-Weight Alginate Oligosaccharide Disrupts Pseudomonal Microcolony Formation and Enhances Antibiotic Effectiveness.

In chronic respiratory disease, the formation of dense, 3-dimensional "microcolonies" by Pseudomonas aeruginosa within the airway plays an important role in contributing to resistance to treatment. An in vitro biofilm model of pseudomonal microcolony formation using artificial-sputum (AS) medium was established to study the effects of low-molecular-weight alginate oligomers (OligoG CF-5/20) on pseudomonal growth, microcolony formation, and the efficacy of colistin. The studies employed clinical cystic fibrosis (CF) isolates (n = 3) and reference nonmucoid and mucoid multidrug-resistant (MDR) CF isolates (n = 7). Bacterial growth and biofilm development and disruption were studied using cell viability assays and image analysis with scanning electron and confocal laser scanning microscopy. Pseudomonal growth in AS medium was associated with increased ATP production (P < 0.05) and the formation (at 48 h) of discrete (>10-µm) microcolonies. In conventional growth medium, colistin retained an ability to inhibit growth of planktonic bacteria, although the MIC was increased (0.1 to 0.4 µg/ml) in AS medium compared to Mueller-Hinton (MH) medium. In contrast, in an established-biofilm model in AS medium, the efficacy of colistin was decreased. OligoG CF-5/20 (≥2%) treatment, however, induced dose-dependent biofilm disruption (P < 0.05) and led to colistin retaining its antimicrobial activity (P < 0.05). While circular dichroism indicated that OligoG CF-5/20 did not change the orientation of the alginate carboxyl groups, mass spectrometry demonstrated that the oligomers induced dose-dependent (>0.2%; P < 0.05) reductions in pseudomonal quorum-sensing signaling. These findings reinforce the potential clinical significance of microcolony formation in the CF lung and highlight a novel approach to treat MDR pseudomonal infections.

OligoG CF-5/20 normalizes cystic fibrosis mucus by chelating calcium.

The goal of this study was to determine whether the guluronate (G) rich alginate OligoG CF-5/20 (OligoG) could detach cystic fibrosis (CF) mucus by calcium chelation, which is also required for normal mucin unfolding. Since bicarbonate secretion is impaired in CF, leading to insufficient mucin unfolding and thereby attached mucus, and since bicarbonate has the ability to bind calcium, we hypothesized that the calcium chelating property of OligoG would lead to detachment of CF mucus. Indeed, OligoG could compete with the N-terminus of the MUC2 mucin for calcium binding as shown by microscale thermophoresis. Further, effects on mucus thickness and attachment induced by OligoG and other alginate fractions of different length and composition were evaluated in explants of CF mouse ileum mounted in horizontal Ussing-type chambers. OligoG at 1.5% caused effective detachment of CF mucus and the most potent alginate fraction tested, the poly-G fraction of about 12 residues, had similar potency compared to OligoG whereas mannuronate-rich (M) polymers had minimal effect. In conclusion, OligoG binds calcium with appropriate affinity without any overt harmful effect on the tissue and can be exploited for treating mucus stagnation.

OligoG CF-5/20 Disruption of Mucoid Pseudomonas aeruginosa Biofilm in a Murine Lung Infection Model.

Biofilm growth is a universal survival strategy for bacteria, providing an effective and resilient approach for survival in an otherwise hostile environment. In the context of an infection, a biofilm provides resistance and tolerance to host immune defenses and antibiotics, allowing the biofilm population to survive and thrive under conditions that would destroy their planktonic counterparts. Therefore, the disruption of the biofilm is a key step in eradicating persistent bacterial infections, as seen in many types of chronic disease. In these studies, we used both in vitro minimum biofilm eradication concentration (MBEC) assays and an in vivo model of chronic biofilm infection to demonstrate the biofilm-disrupting effects of an alginate oligomer, OligoG CF-5/20. Biofilm infections were established in mice by tracheal instillation of a mucoid clinical isolate of Pseudomonas aeruginosa embedded in alginate polymer beads. The disruption of the biofilm by OligoG CF-5/20 was observed in a dose-dependent manner over 24 h, with up to a 2.5-log reduction in CFU in the infected mouse lungs. Furthermore, in vitro assays showed that 5% OligoG CF-5/20 significantly reduced the MBEC for colistin from 512 µg/ml to 4 µg/ml after 8 h. These findings support the potential for OligoG CF-5/20 as a biofilm disruption agent which may have clinical value in reducing the microbial burden in chronic biofilm infections.

A New Class of Safe Oligosaccharide Polymer Therapy To Modify the Mucus Barrier of Chronic Respiratory Disease.

The host- and bacteria-derived extracellular polysaccharide coating of the lung is a considerable challenge in chronic respiratory disease and is a powerful barrier to effective drug delivery. A low molecular weight 12-15-mer alginate oligosaccharide (OligoG CF-5/20), derived from plant biopolymers, was shown to modulate the polyanionic components of this coating. Molecular modeling and Fourier transform infrared spectroscopy demonstrated binding between OligoG CF-5/20 and respiratory mucins. Ex vivo studies showed binding induced alterations in mucin surface charge and porosity of the three-dimensional mucin networks in cystic fibrosis (CF) sputum. Human studies showed that OligoG CF-5/20 is safe for inhalation in CF patients with effective lung deposition and modifies the viscoelasticity of CF-sputum. OligoG CF-5/20 is the first inhaled polymer therapy, represents a novel mechanism of action and therapeutic approach for the treatment of chronic respiratory disease, and is currently in Phase IIb clinical trials for the treatment of CF.

A nanoscale characterization of the interaction of a novel alginate oligomer with the cell surface and motility of Pseudomonas aeruginosa.

Pseudomonas aeruginosa (PA) biofilm-associated infections are a common cause of morbidity in chronic respiratory disease and represent a therapeutic challenge. Recently, the ability of a novel alginate oligomer (OligoG) to potentiate the effect of antibiotics against gram-negative, multi-drug-resistant bacteria and inhibit biofilm formation in vitro has been described. Interaction of OligoG with the cell surface of PA was characterized at the nanoscale using atomic force microscopy (AFM), zeta potential measurement (surface charge), and sizing measurements (dynamic light scattering). The ability of OligoG to modify motility was studied in motility assays. AFM demonstrated binding of OligoG to the bacterial cell surface, which was irreversible after exposure to hydrodynamic shear (5,500 × g). Zeta potential analysis (pH 5-9; 0.1-0.001 M NaCl) demonstrated that binding was associated with marked changes in the bacterial surface charge (-30.9 ± 0.8 to -47.0 ± 2.3 mV; 0.01 M NaCl [pH 5]; P < 0.001). Sizing analysis demonstrated that alteration of surface charge was associated with cell aggregation with a 2- to 3-fold increase in mean particle size at OligoG concentrations greater than 2% (914 ± 284 to 2599 ± 472 nm; 0.01 M NaCl [pH 5]; P < 0.001). These changes were associated with marked dose-dependent inhibition in bacterial swarming motility in PA and Burkholderia spp. The ability of OligoG to bind to a bacterial surface, modulate surface charge, induce microbial aggregation, and inhibit motility represents important direct mechanisms by which antibiotic potentiation and biofilm disruption is affected. These results highlight the value of combining multiple nanoscale technologies to further our understanding of the mechanisms of action of novel antibacterial therapies.

A chemo-enzymatic method for preparation of saturated oligosaccharides from alginate and other uronic acid-containing polysaccharides.

Oligosaccharides from uronic acid-containing polysaccharides can be produced either by chemical or enzymatic degradation. The benefit of using enzymes, called lyases, is their high specificity for various glycosidic linkages. Lyases cleave the polysaccharide chain by an ß-elimination reaction, yielding oligosaccharides with an unsaturated sugar (4-deoxy-l-erythro-hex-4-enepyranosyluronate) at the non-reducing end. In this work we have systematically studied acid degradation of unsaturated uronic acid oligosaccharides. Based on these findings, a method for preparing saturated oligosaccharides by enzymatic degradation of uronic acid-containing polysaccharides was developed. This results in oligosaccharides with a pre-defined distribution and proportion of sugar residues compared to the products of chemical degradation, while maintaining the chemical structure of the non-reducing end. The described method was demonstrated for generating saturated oligosaccharides of alginate, heparin and polygalacturonic acid. In the case of alginate, the ratio of hydrolysis rate of Δ-G and Δ-M linkages to that of G-G and M-M linkages, respectively, was found to be approximately 65 and 43, at pH* 3.4, 90 °C. Finally, this method has been demonstrated to be superior in the production of α-l-guluronate oligosaccharides with a lower content of ß-d-mannuronate residues compared to what can be achieved using chemical depolymerization alone.

Alginate oligosaccharides enhance the antifungal activity of nystatin against candidal biofilms.

Background: The increasing prevalence of invasive fungal infections in immuno-compromised patients is a considerable cause of morbidity and mortality. With the rapid emergence of antifungal resistance and an inadequate pipeline of new therapies, novel treatment strategies are now urgently required. Methods: The antifungal activity of the alginate oligosaccharide OligoG in conjunction with nystatin was tested against a range of Candida spp. (C. albicans, C. glabrata, C. parapsilosis, C. auris, C. tropicalis and C. dubliniensis), in both planktonic and biofilm assays, to determine its potential clinical utility to enhance the treatment of candidal infections. The effect of OligoG (0-6%) ± nystatin on Candida spp. was examined in minimum inhibitory concentration (MIC) and growth curve assays. Antifungal effects of OligoG and nystatin treatment on biofilm formation and disruption were characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and ATP cellular viability assays. Effects on the cell membrane were determined using permeability assays and transmission electron microscopy (TEM). Results: MIC and growth curve assays demonstrated the synergistic effects of OligoG (0-6%) with nystatin, resulting in an up to 32-fold reduction in MIC, and a significant reduction in the growth of C. parapsilosis and C. auris (minimum significant difference = 0.2 and 0.12 respectively). CLSM and SEM imaging demonstrated that the combination treatment of OligoG (4%) with nystatin (1 µg/ml) resulted in significant inhibition of candidal biofilm formation on glass and clinical grade silicone surfaces (p < 0.001), with increased cell death (p < 0.0001). The ATP biofilm disruption assay demonstrated a significant reduction in cell viability with OligoG (4%) alone and the combined OligoG/nystatin (MIC value) treatment (p < 0.04) for all Candida strains tested. TEM studies revealed the combined OligoG/nystatin treatment induced structural reorganization of the Candida cell membrane, with increased permeability when compared to the untreated control (p < 0.001). Conclusions: Antimicrobial synergy between OligoG and nystatin against Candida spp. highlights the potential utility of this combination therapy in the prevention and topical treatment of candidal biofilm infections, to overcome the inherent tolerance of biofilm structures to antifungal agents.

Structure-Activity Relationships of Low Molecular Weight Alginate Oligosaccharide Therapy against Pseudomonas aeruginosa.

Low molecular weight alginate oligosaccharides have been shown to exhibit anti-microbial activity against a range of multi-drug resistant bacteria, including Pseudomonas aeruginosa. Previous studies suggested that the disruption of calcium (Ca2+)-DNA binding within bacterial biofilms and dysregulation of quorum sensing (QS) were key factors in these observed effects. To further investigate the contribution of Ca2+ binding, G-block (OligoG) and M-block alginate oligosaccharides (OligoM) with comparable average size DPn 19 but contrasting Ca2+ binding properties were prepared. Fourier-transform infrared spectroscopy demonstrated prolonged binding of alginate oligosaccharides to the pseudomonal cell membrane even after hydrodynamic shear treatment. Molecular dynamics simulations and isothermal titration calorimetry revealed that OligoG exhibited stronger interactions with bacterial LPS than OligoM, although this difference was not mirrored by differential reductions in bacterial growth. While confocal laser scanning microscopy showed that both agents demonstrated similar dose-dependent reductions in biofilm formation, OligoG exhibited a stronger QS inhibitory effect and increased potentiation of the antibiotic azithromycin in minimum inhibitory concentration and biofilm assays. This study demonstrates that the anti-microbial effects of alginate oligosaccharides are not purely influenced by Ca2+-dependent processes but also by electrostatic interactions that are common to both G-block and M-block structures.

Alginate oligosaccharides enhance diffusion and activity of colistin in a mucin-rich environment.

In a number of chronic respiratory diseases e.g. cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), the production of viscous mucin reduces pulmonary function and represents an effective barrier to diffusion of inhaled therapies e.g. antibiotics. Here, a 2-compartment Transwell model was developed to study impaired diffusion of the antibiotic colistin across an artificial sputum (AS) matrix/medium and to quantify its antimicrobial activity against Pseudomonas aeruginosa NH57388A biofilms (alone and in combination with mucolytic therapy). High-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) revealed that the presence of AS medium significantly reduced the rate of colistin diffusion (> 85% at 48 h; p < 0.05). Addition of alginate oligosaccharide (OligoG CF-5/20) significantly improved colistin diffusion by 3.7 times through mucin-rich AS medium (at 48 h; p < 0.05). Increased diffusion of colistin with OligoG CF-5/20 was shown (using confocal laser scanning microscopy and COMSTAT image analysis) to be associated with significantly increased bacterial killing (p < 0.05). These data support the use of this model to study drug and small molecule delivery across clinically-relevant diffusion barriers. The findings indicate the significant loss of colistin and reduced effectiveness that occurs with mucin binding, and support the use of mucolytics to improve antimicrobial efficacy and lower antibiotic exposure.

Evaluating the alginate oligosaccharide (OligoG) as a therapy for Burkholderia cepacia complex cystic fibrosis lung infection.

OligoG has previously shown potentiation of aztreonam against Burkholderia cepacia complex (Bcc) through biofilm disruption. A randomized, double-blind, placebo-controlled cross-over design was used to evaluate safety and efficacy of inhaled OligoG as a therapy for Bcc-infected CF patients taking aztreonam. Subjects received OligoG (1050 mg daily) or matching placebo for 28-days. Of 14 subjects completing the study, 8 showed a mean decrease in total bacterial CFU's (0.82 log10) after OligoG treatment. There was a reduction in mean Bcc CFU's (2.19 log10) after OligoG treatment but this was not statistically significant. Rheology analysis showed improvements in phase-angle after OligoG, but there was no statistically significant improvement in lung function parameters. Six out of 12 QoL summary scores showed relative improvement after OligoG treatment compared to placebo. There was a favourable safety profile for OligoG. Potential for reducing Bcc warrants further investigation of OligoG for the treatment of infection in CF.

Implementation of microbiota analysis in clinical trials for cystic fibrosis lung infection: Experience from the OligoG phase 2b clinical trials.

Culture-independent microbiota analysis is widely used in research and being increasingly used in translational studies. However, methods for standardisation and application of these analyses in clinical trials are limited. Here we report the microbiota analysis that accompanied two phase 2b clinical trials of the novel, non-antibiotic therapy OligoG CF-5/20 for cystic fibrosis (CF) lung infection. Standardised protocols (DNA extraction, PCR, qPCR and 16S rRNA gene sequencing analysis) were developed for application to the Pseudomonas aeruginosa (NCT02157922) and Burkholderia cepacia complex (NCT02453789) clinical trials involving 45 and 13 adult trial participants, respectively. Microbiota analysis identified that paired sputum samples from an individual participant, taken within 2 h of each other, had reproducible bacterial diversity profiles. Although culture microbiology had identified patients as either colonised by P. aeruginosa or B. cepacia complex species at recruitment, microbiota analysis revealed patient lung infection communities were not always dominated by these key CF pathogens. Microbiota profiles were patient-specific and remained stable over the course of both clinical trials (6 sampling points over the course of 140 days). Within the Burkholderia trial, participants were infected with B. cenocepacia (n = 4), B. multivorans (n = 6), or an undetermined species (n = 3). Colonisation with either B. cenocepacia or B. multivorans influenced the overall bacterial community structure in sputum. Overall, we have shown that sputum microbiota in adults with CF is stable over a 2 h time-frame, suggesting collection of a single sample on a collection day is sufficient to capture the microbiota diversity. Despite the uniform pathogen culture-positivity status at recruitment, trial participants were highly heterogeneous in their lung microbiota. Understanding the microbiota profiles of individuals with CF ahead of future clinical trials would be beneficial in the context of patient stratification and trial design.

Phenotypic and Genotypic Adaptations in Pseudomonas aeruginosa Biofilms following Long-Term Exposure to an Alginate Oligomer Therapy.

Chronic Pseudomonas aeruginosa lung infections in cystic fibrosis (CF) evolve to generate environmentally adapted biofilm communities, leading to increased patient morbidity and mortality. OligoG CF-5/20, a low-molecular-weight inhaled alginate oligomer therapy, is currently in phase IIb/III clinical trials in CF patients. Experimental evolution of P. aeruginosa in response to OligoG CF-5/20 was assessed using a bead biofilm model allowing continuous passage (45 days; ∼245 generations). Mutants isolated after OligoG CF-5/20 treatment typically had a reduced biofilm-forming ability and altered motility profile. Genotypically, OligoG CF-5/20 provided no selective pressure on genomic mutations within morphotypes. Chronic exposure to azithromycin, a commonly prescribed antibiotic in CF patients, with or without OligoG CF-5/20 in the biofilm evolution model also had no effect on rates of resistance acquisition. Interestingly, however, cross-resistance to other antibiotics (e.g., aztreonam) was reduced in the presence of OligoG CF-5/20. Collectively, these findings show no apparent adverse effects from long-term exposure to OligoG CF-5/20, instead resulting in both fewer colonies with multidrug resistance (MDR)-associated phenotypes and improved antibiotic susceptibility of P. aeruginosaIMPORTANCE The emergence of multidrug-resistant (MDR) pathogens within biofilms in the cystic fibrosis lung results in increased morbidity. An inhalation therapy derived from alginate, OligoG CF-5/20, is currently in clinical trials for cystic fibrosis patients. OligoG CF-5/20 has been shown to alter sputum viscoelasticity, disrupt mucin polymer networks, and disrupt MDR pseudomonal biofilms. Long-term exposure to inhaled therapeutics may induce selective evolutionary pressures on bacteria within the lung biofilm. Here, a bead biofilm model with repeated exposure of P. aeruginosa to OligoG CF-5/20 (alone and in combination with azithromycin) was conducted to study these long-term effects and characterize the phenotypic and genotypic adaptations which result. These findings, over 6 weeks, show that long-term use of OligoG CF-5/20 does not lead to extensive mutational changes and may potentially decrease the pathogenicity of the bacterial biofilm and improve the susceptibility of P. aeruginosa to other classes of antibiotics.

Bi-Functional Alginate Oligosaccharide-Polymyxin Conjugates for Improved Treatment of Multidrug-Resistant Gram-Negative Bacterial Infections.

The recent emergence of resistance to colistin, an antibiotic of last resort with dose-limiting toxicity, has highlighted the need for alternative approaches to combat infection. This study aimed to generate and characterise alginate oligosaccharide ("OligoG")-polymyxin (polymyxin B and E (colistin)) conjugates to improve the effectiveness of these antibiotics. OligoG-polymyxin conjugates (amide- or ester-linked), with molecular weights of 5200-12,800 g/mol and antibiotic loading of 6.1-12.9% w/w, were reproducibly synthesised. In vitro inflammatory cytokine production (tumour necrosis factor alpha (TNFα) ELISA) and cytotoxicity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) of colistin (2.2-9.3-fold) and polymyxin B (2.9-27.2-fold) were significantly decreased by OligoG conjugation. Antimicrobial susceptibility tests (minimum inhibitory concentration (MIC), growth curves) demonstrated similar antimicrobial efficacy of ester- and amide-linked conjugates to that of the parent antibiotic but with more sustained inhibition of bacterial growth. OligoG-polymyxin conjugates exhibited improved selectivity for Gram-negative bacteria in comparison to mammalian cells (approximately 2-4-fold). Both OligoG-colistin conjugates caused significant disruption of Pseudomonas aeruginosa biofilm formation and induced bacterial death (confocal laser scanning microscopy). When conjugates were tested in an in vitro "time-to-kill" (TTK) model using Acinetobacter baumannii, only ester-linked conjugates reduced viable bacterial counts (~2-fold) after 4 h. Bi-functional OligoG-polymyxin conjugates have potential therapeutic benefits in the treatment of multidrug-resistant (MDR) Gram-negative bacterial infections, directly reducing toxicity whilst retaining antimicrobial and antibiofilm activities.

Inhaled dry powder alginate oligosaccharide in cystic fibrosis: a randomised, double-blind, placebo-controlled, crossover phase 2b study.

BACKGROUND: OligoG is a low molecular-weight alginate oligosaccharide that improves the viscoelastic properties of cystic fibrosis (CF) mucus and disrupts biofilms, thereby potentiating the activity of antimicrobial agents. The efficacy of inhaled OligoG was evaluated in adult patients with CF. METHODS: A randomised, double-blind, placebo-controlled multicentre crossover study was used to demonstrate safety and efficacy of inhaled dry powder OligoG. Subjects were randomly allocated to receive OligoG 1050 mg per day (10 capsules three times daily) or matching placebo for 28 days, with 28-day washout periods following each treatment period. The primary end-point was absolute change in percentage predicted forced expiratory volume in 1 s (FEV1) at the end of 28-day treatment. The intention-to-treat (ITT) population (n=65) was defined as randomised to treatment with at least one administration of study medication and post-dosing evaluation. RESULTS: In this study, 90 adult subjects were screened and 65 were randomised. Statistically significant improvement in FEV1 was not observed in the ITT population. Adverse events included nasopharyngitis, cough and pulmonary exacerbation. The number and proportions of patients with adverse events and serious adverse events were similar between OligoG and placebo group. CONCLUSIONS: Inhalation of OligoG-dry powder over 28 days was safe in adult CF subjects. Statistically significant improvement of FEV1 was not reached. The planned analyses did not indicate a significant treatment benefit with OligoG compared to placebo. Post hoc exploratory analyses showed subgroup results that indicate that further studies of OligoG in this patient population are justified.

The antimicrobial effects of the alginate oligomer OligoG CF-5/20 are independent of direct bacterial cell membrane disruption.

Concerns about acquisition of antibiotic resistance have led to increasing demand for new antimicrobial therapies. OligoG CF-5/20 is an alginate oligosaccharide previously shown to have antimicrobial and antibiotic potentiating activity. We investigated the structural modification of the bacterial cell wall by OligoG CF-5/20 and its effect on membrane permeability. Binding of OligoG CF-5/20 to the bacterial cell surface was demonstrated in Gram-negative bacteria. Permeability assays revealed that OligoG CF-5/20 had virtually no membrane-perturbing effects. Lipopolysaccharide (LPS) surface charge and aggregation were unaltered in the presence of OligoG CF-5/20. Small angle neutron scattering and circular dichroism spectroscopy showed no substantial change to the structure of LPS in the presence of OligoG CF-5/20, however, isothermal titration calorimetry demonstrated a weak calcium-mediated interaction. Metabolomic analysis confirmed no change in cellular metabolic response to a range of osmolytes when treated with OligoG CF-5/20. This data shows that, although weak interactions occur between LPS and OligoG CF-5/20 in the presence of calcium, the antimicrobial effects of OligoG CF-5/20 are not related to the induction of structural alterations in the LPS or cell permeability. These results suggest a novel mechanism of action that may avoid the common route in acquisition of resistance via LPS structural modification.

A novel guluronate oligomer improves intestinal transit and survival in cystic fibrosis mice.

BACKGROUND: Cystic fibrosis (CF) patients experience intestinal complications characterized by the accumulation of thick viscous mucus. CF mice were utilized to determine if a novel guluronate oligomer, OligoG, may be a potential therapy in reducing intestinal mucus and subsequent CF-related intestinal manifestations. METHODS: Intestinal transit, intestinal histology, survival and growth were examined in wildtype and CF mice on regular water and OligoG. CONCLUSIONS: OligoG improves intestinal transit and survival in CF mice by reducing the accumulation of intestinal mucus. OligoG's ability to directly bind mucin, disrupt mucin interaction and/or sequester calcium allowing for mucin expansion may explain the decrease in mucus accumulation.