From healing wounds to resorbable electronics, levan can fill bioadhesive roles in scores of markets

Effect of Tight Junction-Modulating FCIGRL-Modified Peptides on the Intestinal Absorption of Doxorubicin in Rats

Doxorubicin is a potent chemotherapy drug, but its oral bioavailability is limited due to its low membrane permeability. Thus, absorption enhancers such as zonula occludens toxin and its six-mer fragment, FCIGRL, have been studied to address this issue. This study aimed to evaluate the effectiveness of four peptides (Pep1, Pep2, Pep3, and Pep4) derived from FCIGRL and investigate the changes in the absorption of doxorubicin, to propose an absorption enhancer for doxorubicin. Pep1 is a modified version of FCIGRL in which the hydroxyl group at the C-terminus is replaced with an amino group. Pep2 is a modified Pep1 in which cysteine is replaced with N3-substituted dipropionic acid. Pep3 and Pep4 are Pep2-modified homodimers. Pharmacokinetic analysis was performed in rats after the intraduodenal administration of doxorubicin solutions containing each FCIGRL-modified peptide and the stabilizer levan or benzalkonium chloride (BC). The results showed that Pep3 and Pep4 administered with levan each significantly increased the intestinal absorption of doxorubicin, as did Pep2 administered with levan/BC. In particular, 10 mg·kg-1 of Pep4 with levan significantly increased the area under the curve (AUC)0-240min of doxorubicin by 2.38-fold (p < 0.01) and the peak concentration (Cmax) by 3.30-fold (p < 0.01) compared to the control solution. The study findings indicate that Pep2, Pep3, and primarily Pep4 are novel absorption enhancers that can open tight junctions for doxorubicin, and the effectiveness of the peptides was directly affected by the presence of levan or levan/BC.

Characterization of Levan Fructan Produced by a Gluconobacter japonicus Strain Isolated from a Sugarcane Processing Facility

During raw sugarcane processing, a significant portion of lost sucrose is attributable to microbial degradation. Sucrose consumption by many bacteria is also linked to the production of exopolysaccharides (EPS) such as dextrans and fructans. These resulting EPS cause operational challenges during raw sugar manufacturing. Here, we report the characterization of EPS from a fructan-forming Gluconobacter japonicus bacterium that we previously isolated from a Louisiana sugarcane factory. The genome sequencing revealed the presence of two encoded levansucrase genes, lsrA and lsrB. One levansucrase, LsrB, was detected in the secreted protein fraction of G. japonicus LASM12 by QTOF LC-MS. The spotting assays indicated that G. japonicus produces EPS using sucrose and raffinose as substrates. The G. japonicus EPS correlated with levan fructan commercial standards by 1H-NMR, and with the characteristic carbohydrate fingerprint region for FTIR spectra, confirming that the G. japonicus EPS is levan fructan. The glycosyl composition and glycosyl linkage analysis revealed a linear β-2,6-fructofuranosyl polysaccharide with occasional (5.7%) β-2,1-fructofuranosyl branches. The gel permeation chromatography of the levan fructan EPS showed two main peaks at 4.5 kDa and 8 kDa and a very minor peak at 500 kDa. G. japonicus was identified as a producer of levan fructan. These findings will be useful for future studies aimed at evaluating the impact of levan fructans on sugar crop processing, which have been historically underestimated in industry.

First transcriptomic insight into the reprogramming of human macrophages by levan-type fructans

Based on stimuli in the biological milieu, macrophages can undergo classical activation into the M1 pro-inflammatory (anti-cancer) phenotype or to the alternatively activated M2 anti-inflammatory one. Drug-free biomaterials have emerged as a new therapeutic strategy to modulate macrophage phenotype. Among them, polysaccharides polarize macrophages to M1 or M2 phenotypes based on the surface receptors they bind. Levan, a fructan, has been proposed as a novel biomaterial though its interaction with macrophages has been scarcely explored. In this study, we investigate the interaction of non-hydrolyzed and hydrolyzed Halomonas levan and its sulfated derivative with human macrophages in vitro. Viability studies show that these levans are cell compatible. In addition, RNA-sequencing analysis reveals the upregulation of pro-inflammatory pathways. These results are in good agreement with real time-quantitative polymerase chain reaction that indicates higher expression levels of C-X-C Motif Chemokine Ligand 8 and interleukin-6 genes and the M2-to-M1 reprogramming of these cells upon levan treatment. Finally, cytokine release studies confirm that hydrolyzed levans increase the secretion of pro-inflammatory cytokines and reprogram IL-4-polarized macrophages to the M1 state. Overall findings indicate that Halomonas levans trigger a classical macrophage activation and pave the way for their application in therapeutic interventions requiring a pro-inflammatory phenotype.

Exploring the potential of Halomonas levan and its derivatives as active ingredients in cosmeceutical and skin regenerating formulations

Demand on natural products that contain biological ingredients mimicking growth factors and cytokines made natural polysaccharides popular in pharmaceutical and cosmetic industries. Levan is the β-(2-6) linked, nontoxic, biocompatible, water-soluble, film former fructan polymer that has diverse applications in pharmacy and cosmeceutical industries with its moisturizing, whitening, anti-irritant, anti-aging and slimming activities. Driven by the limited reports on few structurally similar levan polymers, this study presents the first systematic investigation on the effects of structurally different extremophilic Halomonas levan polysaccharides on human skin epidermis cells. In-vitro experiments with microbially produced linear Halomonas levan (HL), its hydrolyzed, (hHL) and sulfonated (ShHL) derivatives as well as enzymatically produced branched levan (EL) revealed increased keratinocyte and fibroblast proliferation (113-118 %), improved skin barrier function through induced expressions of involucrin (2.0 and 6.43 fold changes for HL and EL) and filaggrin (1.74 and 3.89 fold changes for hHL and ShHL) genes and increased type I collagen (2.63 for ShHL) and hyaluronan synthase 3 (1.41 for HL) gene expressions together with fast wound healing ability within 24 h (100 %, HL) on 2D wound models clearly showed that HL and its derivatives have high potential to be used as natural active ingredients in cosmeceutical and skin regenerating formulations.

Co-production of levan with other high-value bioproducts: A review

Levan is a homopolysaccharide of fructose that has both scientific and industrial importance, with various applications in health, pharmaceutical, cosmetic and food industries. Despite its broad spectrum of uses, there are only a limited number of commercial levan sources due to the high costs related to its production. To make production economically viable, efforts have been concentrated on the selection of levan-producing microorganisms, the genetic manipulation of new strains, and the use of inexpensive agro-industrial byproducts as substrates. Another efficient strategy involves the concomitant synthesis of other products with high market value and as such, the successful co-production of levan was demonstrated with fructooligosaccharides, ethanol, sorbitol, poly-ε-lysine, poly-γ-glutamic acid and polyhydroxyalkanoates. This paper offers a systematic review of important aspects regarding recent strategies involving the simultaneous synthesis of levan and other bioproducts of aggregate value reported to date and discusses the challenges and opportunities for its large-scale production and applications.

Structural characterization and physicochemical properties of the exopolysaccharide produced by the moderately halophilic bacterium Chromohalobacter salexigens, strain 3EQS1

A strain, 3EQS1, was isolated from a salt sample taken from Lake Qarun (Fayoum Province, Egypt). On the basis of physiological, biochemical, and phylogenetic analyses, the strain was classified as Chromohalobacter salexigens. By 72 h of growth at 25 °C, strain 3EQS1 produced large amounts (15.1 g L^-1) of exopolysaccharide (EPS) in a liquid mineral medium (initial pH 8.0) containing 10% sucrose and 10% NaCl. The EPS was precipitated from the cell-free culture medium with chilled ethanol and was purified by gel-permeation and anion-exchange chromatography. The molecular mass of the EPS was 0.9 × 10⁶ Da. Chemical analyses, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy showed that the EPS was a linear β-D-(2 → 6)-linked fructan (levan). In aqueous solution, the EPS tended to form supramolecular aggregates with a critical aggregation concentration of 240 µg mL^-1. The EPS had high emulsifying activity (E₂₄, %) against kerosene (31.2 ± 0.4%), sunflower oil (76.9 ± 1.3%), and crude oil (98.9 ± 0.8%), and it also had surfactant properties. A 0.1% (w/v) aqueous EPS solution reduced the surface tension of water by 11.9%. The levan of C. salexigens 3EQS1 may be useful in various biotechnological processes.

A sticky carbohydrate meets a mussel adhesive: Catechol-conjugated levan for hemostatic and wound healing applications

The stickiest natural polysaccharide, levan, plays a role in metalloproteinase activation, which is an important step involved in the healing of injured tissue. However, levan is easily diluted, washed away, and loses adhesion in wet environments, which limits its biomedical applications. Herein, we demonstrate a strategy for fabricating a levan-based adhesive hydrogel for hemostatic and wound healing applications by conjugating catechol to levan. Prepared hydrogels exhibit significantly improved water solubilities, and adhesion strengths to hydrated porcine skin of up to 42.17 ± 0.24 kPa which is more than three-times that of fibrin glue adhesive. The hydrogels also promote rapid blood clotting and significantly faster healing of rat-skin incisions compared to nontreated samples. In addition, levan-catechol exhibited an immune response close to that of the negative control, which is ascribable to its significantly lower endotoxin level compared to native levan. Overall, levan-catechol hydrogels are promising materials for hemostatic and wound healing applications.

Erwinia tasmaniensis levansucrase shows enantiomer selection for (S)-1,2,4-butanetriol

Levansucrases are biotechnologically interesting fructosyltransferases due to their potential use in the enzymatic or chemo-enzymatic synthesis of glycosides of non-natural substrates relevant to pharmaceutical applications. The structure of Erwinia tasmaniensis levansucrase in complex with (S)-1,2,4-butanetriol and its biochemical characterization suggests the possible application of short aliphatic moieties containing polyols with defined stereocentres in fructosylation biotechnology. The structural information revealed that (S)-1,2,4-butanetriol mimics the natural substrate. The preference of the protein towards a specific 1,2,4-butanetriol enantiomer was assessed using microscale thermophoresis binding assays. Furthermore, the results obtained and the structural comparison of levansucrases and inulosucrases suggest that the fructose binding modes could differ in fructosyltransferases from Gram-positive and Gram-negative bacteria.

Synthesis and characterization of levan hydrogels and their use for resveratrol release

Considering the need for systematic studies on levan based hydrogels to widen their use in drug delivery systems and biomedical applications, this study is mainly focused on the synthesis and comprehensive characterization as well as drug release properties of hydrogels based on Halomonas levan (HL) and its chemical derivatives. For this, hydrolyzed and phosphonated HL derivatives were chemically synthesized and then cross-linked with 1,4-Butanediol diglycidyl ether (BDDE) and the obtained hydrogels were characterized in terms of their swelling, adhesivity, and rheological properties. Both native and phosphonated HL hydrogels retained their rigid gel like structure with increasing shear stress levels and tack test analysis showed superior adhesive properties of the phosphonated HL hydrogels. Moreover, hydrogels were loaded with resveratrol and entrapment and release studies as well as cell culture studies with human keratinocytes were performed. Biocompatible and adhesive features of the hydrogels confirmed their suitability for tissue engineering and drug delivery applications.

The Structure of Sucrose-Soaked Levansucrase Crystals from Erwinia tasmaniensis reveals a Binding Pocket for Levanbiose

Given its potential role in the synthesis of novel prebiotics and applications in the pharmaceutical industry, a strong interest has developed in the enzyme levansucrase (LSC, EC 2.4.1.10). LSC catalyzes both the hydrolysis of sucrose (or sucroselike substrates) and the transfructosylation of a wide range of acceptors. LSC from the Gram-negative bacterium Erwinia tasmaniensis (EtLSC) is an interesting biocatalyst due to its high-yield production of fructooligosaccharides (FOSs). In order to learn more about the process of chain elongation, we obtained the crystal structure of EtLSC in complex with levanbiose (LBS). LBS is an FOS intermediate formed during the synthesis of longer-chain FOSs and levan. Analysis of the LBS binding pocket revealed that its structure was conserved in several related species. The binding pocket discovered in this crystal structure is an ideal target for future mutagenesis studies in order to understand its biological relevance and to engineer LSCs into tailored products.

A comprehensive study on levan nanoparticles formation: Kinetics and self-assembly modeling

Levan nanoparticles formation is a complicated phenomenon involving simultaneously polymeric reaction kinetics and nanoparticles self-assembly theory. These phenomena are studied in this work with experimental and computational methodologies. Specifically, the effect of different parameters on levan kinetics and nanoparticles production in a cell-free system environment have been studied. Results point out that 37 °C is the best temperature for synthesizing levan as well as the existence of a substrate inhibition effect for polymeric reaction. This work also highlights that raffinose can be used for producing and that an increase on the ratio enzyme-substrate increases the velocity of conversion. However, the previous experimental conditions did not produce an important effect on self-assembly formed levan nanoparticles (always 110 nm) as long as the required levan concentration (CAC) for nanoparticles reorganization is achieved. To have a better understanding of these results, a model was developed to explain numerically levan kinetics and nanoparticle self-assembly. This model was built by taking into account enzyme poisoning effect (also demonstrated experimentally) and a diffusion limited cluster model for the aggregation phenomenon. Simulation results fit properly experimental data and catalytic parameters as well as predicting accurately the value of CAC for producing its reorganization into nanoparticles by self-assembly.

Efficient production of levan using a recombinant yeast Saccharomyces cerevisiae hypersecreting a bacterial levansucrase

Levan is a fructose polymer with diverse applications in the food and medical industries. In this study, levansucrase from Rahnella aquatilis (RaLsrA) was hyper-secreted using a Saccharomyces cerevisiae protein secretion system. An optimal secretion signal, a translation fusion partner (TFP) containing an N-terminal 98 amino acid domain from a mitochondrial inner membrane protein, UTH1, was employed to secrete approximately 50 U/mL of bioactive RaLsrA into culture media with 63% secretion efficiency by fed-batch fermentation. Although the purified RaLsrA was useful for enzymatic conversion of high-molecular-weight levan of approximately 3.75 × 10⁶ Da, recombinant yeast secreting RaLsrA could produce levan more efficiently by microbial fermentation. In a 50-L scale fermenter, 76-g/L levan was directly converted from 191-g/L sucrose by recombinant yeast cells, attaining an 80% conversion yield and 3.17-g/L/h productivity. Thus, we developed a cost-effective and industrially applicable production system for food-grade levan.