A high field NMR study of the products ensuing from konjak glucomannan C(6)-oxidation followed by enzymatic C(5)-epimerization

Isolation, purification, and physicochemical characterization of Polygonatum polysaccharide and its protective effect against CCl4-induced liver injury via Nrf2 and NF-κB signaling pathways

This study aimed to provide scientific evidence that Polygonatum polysaccharide can be developed as a dietary supplement and medication for treating liver injuries. A water-soluble polysaccharide (PSP-N-c-1), with an average molecular weight of 3.45 kDa, was isolated and purified from the water extract of Polygonatum using DEAE cellulose column chromatography, CL-6B agarose gel chromatography, and Sephadex G100 chromatography. High-performance liquid chromatography, gas chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy analyses revealed that PSP-N-c-1 might be linear α-(1 → 4)-glucans with α-Glcp residues linked to the backbone at C-6. In vitro experiments revealed that PSP-N-c-1 exhibited protective effects against CCl4-induced damage in HepG2 cells. In vivo experiments demonstrated that PSP-N-c-1 exhibited a hepatoprotective effect by enhancing antioxidant enzyme activity, inhibiting lipid peroxidation, and reducing the activity of pro-inflammatory mediators. Besides, PSP-N-c-1 could attenuate oxidative stress and inflammatory responses by activating the Nrf2-mediated signaling pathways and regulating the TLR4-mediated NF-κB signaling pathways. These findings demonstrated that PSP-N-c-1 may serve as a supplement for alleviating chemical liver damage.

Structural insight into a glucomannan-type extracellular polysaccharide produced by a marine Bacillus altitudinis SORB11 from Southern Ocean

Extracellular polysaccharide (EPS) produced by a deep-sea, psychrotolerant Bacillus altitudinis SORB11 was evaluated by considering physiochemical nature and structural constituents. The productivity of crude EPS was measured ~ 13.17 g L^-1. The surface topography of the crude EPS showed a porous, webbed structure along with a branched coil-like configuration. The crystalline crude EPS contained a high amount of sulfur. Further, the crude EPS was subjected for purification. The molecular weight of purified EPS was determined ~ 9.8 × 10⁴ Da. The purified EPS was appeared to show glucomannan-like configuration that is composed of → 4)-β-Manp-(1 → and → 4)-β-Glcp-(1 → residues. So, this polysaccharide was comparable to the structure of plant-derived glucomannan. Subsequently, EPS biosynthesis protein clusters like EpsC, EpsD, EpsE, and glycosyltransferase family proteins were predicted from the genome of strain SORB11, which may provide an insight into the production of glucomannan-type of polysaccharide. This low molecular weight linear form of glucomannan-type EPS might be involved to form a network-like unattached aggregation, and helps in cell-to-cell interaction in deep-sea microbial species.

Engineering of konjac glucomannan into respirable microparticles for delivery of antitubercular drugs

Few medically-approved excipients are available for formulation strategies to endow microcarriers with improved performance in lung drug targeting. Konjac glucomannan (KGM) is a novel, biocompatible material, comprising mannose units potentially inducing macrophage uptake for the treatment of macrophage-mediated diseases. This work investigated spray-dried KGM microparticles as inhalable carriers of model antitubercular drugs, isoniazid (INH) and rifabutin (RFB). The polymer was characterised and different polymer/drug ratios tested in the production of microparticles for which respirability was assessed in vitro. The swelling of KGM microparticles and release of drugs in simulated lung fluid were characterised and the biodegradability in presence of β-mannosidase, a lung hydrolase, determined. KGM microparticles were drug loaded with 66-91% association efficiency and had aerodynamic diameter around 3 µm, which enables deep lung penetration. The microparticles swelled upon liquid contact by 40-50% but underwent size reduction (>62% in 90 min) in presence of β-mannosidase, indicating biodegradability. Finally, drug release was tested showing slower release of RFB compared with INH but complete release of both within 24 h. This work identifies KGM as a biodegradable polymer of natural origin that can be engineered to encapsulate and release drugs in respirable microparticles with physical and chemical macrophage-targeting properties.

Properties and potential applications of mannuronan C5-epimerase: A biotechnological tool for modifying alginate

Given the excellent characteristics of alginate, it is an industrially important polysaccharide. Mannuronan C5-epimerase (MC5E) is an alginate-modifying enzyme that catalyzes the conversion of β-D-mannuronate (M) to its C5 epimer α-L-guluronate (G) in alginate. Both the biological activities and physical properties of alginate are determined by M/G ratios and distribution patterns. Therefore, MC5E is regarded as a biotechnological tool for modifying and processing alginate. Various MC5Es derived from brown algae, Pseudomonas and Azotobacter have been isolated and characterized. With the rapid development of structural biology, the crystal structures and catalytic mechanisms of several MC5Es have been elucidated. It is necessary to comprehensively understand the research status of this alginate-modifying enzyme. In this review, the properties and potential applications of MC5Es isolated from different kinds of organisms are summarized and reviewed. Moreover, future research directions of MC5Es as well as strategies to enhance their properties are elucidated, highlighted, and prospected.

Re-evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives

The present opinion deals with the re-evaluation of konjac (E 425), comprising konjac gum (E 425 i) and konjac glucomannan (E 425 ii) when used as food additives. Following the conceptual framework for the risk assessment of certain food additives re-evaluated under Commission Regulation (EU) No 257/2010, the Panel considered that current use of konjac (E 425) was limited in all food categories to maximum permitted level (MPL) of 10 g/kg, and that the calculated indicative refined exposure assessment for all population groups was below 0.1 mg/kg body weight (bw) per day for the general population (mean and high level). Konjac gum and konjac glucomannan were unlikely to be absorbed intact and were significantly fermented by intestinal microbiota. The available database on toxicological studies was considered limited, however, no relevant adverse effects were seen in rats and dogs in 90-day feeding studies according to the SCF, the no-observed-effect level (NOEL) in rats being 1,250 mg konjac glucomannan/kg bw per day. Konjac gum and konjac glucomannan were of no concern with respect to the genotoxicity. After a daily dosage of 3,000 mg in adults for 12 weeks, several individuals experienced abdominal discomfort including diarrhoea or constipation. The Panel concluded that there was no need for a numerical acceptable daily intake (ADI) and that there was no safety concern for the general population at the refined exposure assessment for the reported uses of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives under the current conditions of use of 10 g/kg. The Panel agreed with the conclusions of the SCF (1997) that the uses of konjac (E 425) as an additive at the levels up to 10 g/kg in food are acceptable, provided that the total intake from all sources stays below 3 g/day.

Study on Dendrobium officinale O-acetyl-glucomannan (Dendronan®): part II. Fine structures of O-acetylated residues

Main objective of this study was to investigate the detailed structural information about O-acetylated sugar residues in Dendronan(®). A water solution (2%, w/w) of Dendronan(®) was treated with endo-β-mannanase to produce oligosaccharides rich in O-acetylated sugar residues. The oligosaccharides were partly recovered by ethanol precipitation (70%, w/w). The recovered sample (designated Hydrolyzed Dendrobium officinale Polysaccharide, HDOP) had a yield of 24.7% based on the dry weight of Dendronan(®) and was highly O-acetylated. A D2O solution of HDOP (6%, w/w) generated strong signals in (1)H, (13)C, 2D (1)H-(1)H COSY, 2D (1)H-(1)H TOCSY, 2D (1)H-(1)H NOESY, 2D (1)H-(13)C HMQC, and 2D (1)H-(13)C HMBC NMR spectra. Results of NMR analyses showed that the majority of O-acetylated mannoses were mono-substituted with acetyl groups at O-2 or O-3 position. There were small amounts of mannose residues with di-O-acetyl substitution at both O-2 and O-3 positions. Minor levels of mannoses with 6-O-acetyl, 2,6-di-O-acetyl, and 3,6-di-O-acetyl substitutions were also identified. Much information about sugar residue sequence was extracted from 2D (1)H-(13)C HMBC and 2D (1)H-(1)H NOESY spectra. (1)J(C-H) coupling constants of major sugar residues were obtained. Evidences for the existence of branches or O-acetylated glucoses in HDOP were not found. The major structure of Dendronan(®) is shown as follows: [Formula: see text] M: β-D-mannopyranose; G: β-D-glucopyranose; a: O-acetyl group.

Preparation of Dialdehyde Konjac Glucomamman

Dialdehyde konjac glucomannan (DAKGM) was synthesized by konjac glucomannan via sodium periodate (NaIO4) as an oxidant and characterized by NMR and FTIR spectroscopy techniques. The results indicated that the oxidization of KGM catalyzed by NaIO4was highly selective for C2 and C3 of sugar units to form aldehyde group. Further, the solution behaviors of DAKGM were investigated by steady-state fluorescence. DAKGM exhibited two emission peaks at maximum wavelength 425 nm and 465 nm, respectively.

Biochemical analysis of the processive mechanism for epimerization of alginate by mannuronan C-5 epimerase AlgE4

The enzymes mannuronan C-5 epimerases catalyse the in-chain epimerisation of beta-D-mannuronic acid to alpha-L-guluronic acid in the last step of alginate biosynthesis. The recombinant C-5 epimerase AlgE4, encoded by the soil bacteria Azotobacter vinelandii and expressed in Escherichia coli, exhibits a non-random mode of action when acting on mannuronan and alginates of various monomeric compositions. The observed residue sequence has been suggested previously to be due to either a preferred attack or a processive mode of action. Based on methodologies involving specific degrading enzymes, NMR, electrospray ionisation mass spectrometry and capillary electrophoresis we show here that on average 10 residues are epimerised for each enzyme-substrate encounter. A subsite model for the enzyme is analysed by the same methodology using native and 13C-labelled mannuronan oligomers as substrate for the AlgE4 epimerase. A hexameric oligomer is the minimum size to accommodate activity. For hexa-, hepta- and octameric substrates the third M residue from the non-reducing end is epimerised first.

Effect of deacetylation rate on gelation kinetics of konjac glucomannan

Effect of deacetylation rate on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a degree of acetylation (DA) range of 1.38-10.1 wt.% synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (C(Na)), both the critical gelation times (t(cr)) and the plateau values of storage moduli (G'(sat)) of the KGM gels increased with increasing DA. While at a fixed ratio of alkaline concentrations to values of DA (C(Na)/DA), the similar t(cr) and (G'(sat)) values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the C(Na)/DA on the gelation kinetics of the KGM samples were discussed.

Effect of Degree of Acetylation on Gelation of Konjac Glucomannan

Effect of the degree of acetylation (DA) on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a DA range from 1.38 to 10.1 wt % synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (CNa), both the critical gelation times (tcr) and the plateau values of storage moduli (G'sat) of the KGM gels increased with increasing DA, while at a fixed ratio of alkaline concentrations to values of DA (CNa/DA), similar tcr and values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the CNa/DA on the gelation kinetics of the KGM samples was discussed.