Fine structural features and antioxidant capacity of ferulated arabinoxylans extracted from nixtamalized maize bran.

BACKGROUND: The nixtamalization process improves the nutritional and technological properties of maize. This process generates nixtamalized maize bran as a by-product, which is a source of arabinoxylans (AX). AX are polysaccharides constituted of a xylose backbone with mono- or di-arabinose substitutions, which can be ester-linked to ferulic acid (FA). The present study investigated the fine structural features and antioxidant capacity (AC) of nixtamalized maize bran arabinoxylans (MBAX) to comprehend the structure-radical scavenging capacity relationship in this polysaccharide deeply. RESULTS: MBAX presented a molecular weight, intrinsic viscosity, and hydrodynamic radius of 674 kDa, 1.8 dL g-1 , and 24.6 nm, respectively. The arabinose-to-xylose ratio (A/X) and FA content were 0.74 and 0.25 g kg-1 polysaccharide, respectively. MBAX contained dimers (di-FA) and trimer (tri-FA) of FA (0.14 and 0.07 g kg-1 polysaccharide, respectively). The main di-FA isomer was the 8-5' structure (80%). Fourier transform infrared spectroscopy confirmed MBAX molecular identity, and the second derivate of the spectral data revealed a band at 958 cm-1 related to the presence of arabinose disubstitution. 1 H-Nuclear magnetic resonance spectroscopy showed mono- and di-arabinose substitution in the xylan backbone with more monosubstituted residues. MBAX registered an AC of 25 and 20 µmol Trolox equivalents g-1 polysaccharide despite a low FA content, using ABTS (2,2'-azino-bis-3-ethylbenzthiazoline-6-sulfonic acid) and DPPH (1,1-diphenyl-2-picrylhydrazyl) methods, respectively. CONCLUSION: AC in MBAX could be related to the high A/X ratio (mainly monosubstitution) and the high 8-5' di-FA proportion in this polysaccharide. © 2023 Society of Chemical Industry.

Oral administration of zein-based nanoparticles reduces glycemia and improves glucose tolerance in rats.

The aim was to evaluate the effect of zein-based nanoparticles on the glucose homeostasis, following oral administration to Wistar rats. For this purpose, bare nanoparticles (NP, with tropism for the upper intestinal regions) and poly(ethylene glycol)-coated nanoparticles (NP-PEG), with the capability to reach the ileum and cecum of animals, were evaluated. Both formulations were spherical in shape, displaying sizes around 200 nm and a negative surface zeta potential. The oral administration of a single dose of these nanoparticles to animals (50 mg/kg) induced a significant decrease of the glycemia, compared control rats and in animals treated with the free protein (p < 0.001). Moreover, these nanoparticles improved the glycemic control against an intraperitoneal glucose tolerance test; particularly NP-PEG. These findings would be due to an increased release of glucagon-like peptide-1 (GLP-1) by l-cells, which are more abundant in distal regions of the intestine. In fact, the GLP-1 blood levels of animals treated with nanoparticles were significantly higher than controls (about 40 % and 60 % for NP and NP-PEG groups, respectively). This higher capability of NP-PEG, with respect to NP, to increase the release of GLP-1 and control glycemia would be related to its ability to reach the distal areas of the small intestine.

Arabinoxylans-Based Oral Insulin Delivery System Targeting the Colon: Simulation in a Human Intestinal Microbial Ecosystem and Evaluation in Diabetic Rats.

Arabinoxylans (AX) microcapsules loaded with insulin were prepared by enzymatic gelation of AX, using a triaxial electrospray method. The microcapsules presented a spherical shape, with an average size of 250 µm. The behavior of AX microcapsules was evaluated using a simulator of the human intestinal microbial ecosystem. AX microcapsules were mainly (70%) degraded in the ascending colon. The fermentation was completed in the descending colon, increasing the production of acetic, propionic, and butyric acids. In the three regions of the colon, the fermentation of AX microcapsules significantly increased populations of Bifidobacterium and Lactobacillus and decreased the population of Enterobacteriaceae. In addition, the results found in this in vitro model showed that the AX microcapsules could resist the simulated conditions of the upper gastrointestinal system and be a carrier for insulin delivery to the colon. The pharmacological activity of insulin-loaded AX microcapsules was evaluated after oral delivery in diabetic rats. AX microcapsules lowered the serum glucose levels in diabetic rats by 75%, with insulin doses of 25 and 50 IU/kg. The hypoglycemic effect and the insulin levels remained for more than 48 h. Oral relative bioavailability was 13 and 8.7% for the 25 and 50 IU/kg doses, respectively. These results indicate that AX microcapsules are a promising microbiota-activated system for oral insulin delivery in the colon.

In vivo testing of mucus-permeating nanoparticles for oral insulin delivery using Caenorhabditis elegans as a model under hyperglycemic conditions.

The aim was to evaluate the potential of mucus-permeating nanoparticles for the oral administration of insulin. These nanocarriers, based on the coating of zein nanoparticles with a polymer conjugate containing PEG, displayed a size of 260 nm with a negative surface charge and an insulin payload of 77 µg/mg. In intestinal pig mucus, the diffusivity of these nanoparticles (PPA-NPs) was found to be 20-fold higher than bare nanoparticles (NPs). These results were in line with the biodistribution study in rats, in which NPs remained trapped in the mucus, whereas PPA-NPs were able to cross this layer and reach the epithelium surface. The therapeutic efficacy was evaluated in Caenorhabditis elegans grown under high glucose conditions. In this model, worms treated with insulin-loaded in PPA-NPs displayed a longer lifespan than those treated with insulin free or nanoencapsulated in NPs. This finding was associated with a significant reduction in the formation of reactive oxygen species (ROS) as well as an important decrease in the glucose and fat content in worms. These effects would be related with the mucus-permeating ability of PPA-NPs that would facilitate the passage through the intestinal peritrophic-like dense layer of worms (similar to mucus) and, thus, the absorption of insulin.

An antibiotic potentiator retains its activity after being immobilized on silicone and prevents growth of multidrug-resistant Pseudomonas aeruginosa biofilms.

Device-Associated Healthcare-Associated Infections (DA-HAI) are a major threat to public health worldwide since they are associated with increased hospital stays, morbidity, mortality, financial burden, and hospital overload. A strategy to combat DA-HAI involves the use of medical devices endowed with surfaces that can kill or repel pathogens and prevent biofilm formation. We aimed to develop low-toxic protease-resistant anti-biofilm surfaces that can sensitize drug-resistant bacteria to sub-inhibitory concentrations of antibiotics. To this end, we hypothesized that polymyxin B nonapeptide (PMBN) could retain its antibiotic-enhancing potential upon immobilization on a biocompatible polymer, such as silicone. The ability of PMBN-coated silicone to sensitize a multidrug-resistant clinical isolate of Pseudomonas aeruginosa (strain Ps4) to antibiotics and block biofilm formation was assessed by viable counting, confocal microscopy and safranin uptake. These assays demonstrated that covalently immobilized PMBN enhances not only antibiotics added exogenously but also those incorporated into the functionalized coating. As a result, the functionalized surface exerted a potent bactericidal activity that precluded biofilm formation. PMBN-coated silicone displayed a high level of stability and very low cytotoxicity and hemolytic activity in the presence of antibiotics. We demonstrated for the first time that an antibiotic enhancer can retain its activity when covalently attached to a solid surface. These findings may be applied to the development of medical devices resistant to biofilm formation.

Zein-based nanocarriers for the oral delivery of insulin. In vivo evaluation in Caenorhabditis elegans.

The aim was to evaluate the potential of nanocarriers, based on the coating of zein nanoparticles (ZNP) with a Gantrez® AN-PEG conjugate (GP), for the oral delivery of insulin. ZNP-GP displayed less negative surface charge and a 14-fold higher diffusion coefficient in pig intestinal mucus than ZNP. Both nanoparticles showed a spherical shape and an insulin load of 77.5 µg/mg. Under simulated gastric conditions, ZNP-GP released significantly lower amount of insulin than ZNP, while under simulated intestinal conditions, both types of nanoparticles displayed similar behaviour. In Caenorhabditis elegans wild-type N2, grown under high glucose conditions, insulin treatments reduced glucose and fat accumulation without altering the growth rate, the worm length, or the pumping rate. The effect was significantly greater (p < 0.001) when insulin was nanoencapsulated in ZNP-GP compared with that encapsulated in ZNP or formulated in solution. This would be related to the highest capability of ZNP-GP to diffuse in the dense peritrophic-like layer covering intestinal cells in worms. In daf-2 mutants, the effect on fat and glucose reduction by insulin treatment was suppressed, indicating a DAF-2 dependent mechanism. In summary, ZNP-GP is a promising platform that may offer new opportunities for the oral delivery of insulin and other therapeutic proteins.

Zein-based nanoparticles for the oral delivery of insulin.

The aim of this work was to evaluate oral nanocarriers, prepared from zein nanoparticles coated with a poly(anhydride)-thiamine conjugate (GT), for the delivery of insulin. Nanoparticles displayed a size of 250 nm with a negative surface charge, and an insulin loading of 80 µg/mg. Under simulated gastric conditions, GT-coated nanoparticles released a significantly lower amount of insulin than bare ones; whereas in simulated intestinal conditions, both types of nanoparticles displayed a similar behavior. The effect of insulin on the lipid metabolism of C. elegans under high glucose conditions, characterized by a reduction of the fat content, was also investigated. The effect was significantly higher for the nanoencapsulated forms of insulin than for the free protein (p < 0.001). This effect was two times higher for GT-coated nanoparticles than for bare ones. In rats, the hypoglycemic effect and the pharmacokinetic profile of insulin-loaded nanoparticles orally administered (50 IU/kg) were evaluated. The glycemia of animals slowly decreased reaching a minimum 6-10-h post-administration, with a maximum decrease of about 60%. The pharmacological availability of nanoencapsulated insulin was 13.5%. In serum, nanoparticles provided a maximum of insulin 4-h post-administration, and its relative oral bioavailability was 5.2% (compared with a sc formulation of insulin). Graphical abstract.

Protein-based nanoparticles for drug delivery purposes.

Proteins represent a group of biopolymers with interesting properties to be employed as raw materials in the preparation of nanoparticles for drug delivery purposes. Due to the inherent properties of proteins (i.e., biodegradability, amphiphilic properties, etc.) the resulting nanoparticles can be considered as versatility platforms for a variety of applications. Moreover, some proteins possess a GRAS (Generally Recognized as Safe) status or are considered as excipients by different Regulatory Agencies. As result of this, the resulting nanoparticles and potential translation to clinic would be facilitated, compared to other materials (i.e., polymers). This review is focused on the main proteins employed in the preparation of nanoparticles as well as the procedures permitting their transformation into nanoparticles able of accommodating a high variety of bioactive compounds and drugs. Moreover, the review also provides examples of application of nanoparticles prepared from albumins, globulins, prolamins or macromolecules derived from proteins.

Modulation of the fate of zein nanoparticles by their coating with a Gantrez® AN-thiamine polymer conjugate.

The aim of this work was to evaluate the mucus-permeating properties of nanocarriers using zein nanoparticles (NPZ) coated with a Gantrez® AN-thiamine conjugate (GT). NPZ were coated by incubation at different GT-to-zein ratios: 2.5% coating with GT (GT-NPZ1), 5% (GT-NPZ2) and 10% (GT-NPZ3). During the process, the GT conjugate formed a polymer layer around the surface of zein nanoparticles. For GT-NPZ2, the thickness of this corona was estimated between 15 and 20 nm. These nanocarriers displayed a more negative zeta potential than uncoated NPZ. The diffusivity of nanoparticles was evaluated in pig intestinal mucus by multiple particle tracking analysis. GT-NPZ2 displayed a 28-fold higher diffusion coefficient within the mucus layer than NPZ particles. These results align with in vivo biodistribution studies in which NPZ displayed a localisation restricted to the mucus layer, whereas GT-NPZ2 were capable of reaching the intestinal epithelium. The gastro-intestinal transit of mucoadhesive (NPZ) and mucus-permeating nanoparticles (GT-NPZ2) was also found to be different. Thus, mucoadhesive nanoparticles displayed a significant accumulation in the stomach of animals, whereas mucus-penetrating nanoparticles appeared to exit the stomach more rapidly to access the small intestine of animals.

Enzymatic cross-linking of ferulated arabinoxylan: effect of laccase or peroxidase catalysis on the gel characteristics.

Arabinoxylans (AX) gels at 4% (w/v) were prepared using laccase (LAX gels) or peroxidase (PAX gels), and their cross-linking, rheological, structural, and spectroscopic characteristics were investigated. LAX gels presented lower amount of 5,5'-diferulic acid (11%), smaller mesh size (128 nm), and higher hardness (37 N) and elasticity (430 Pa) than the PAX gels (28%, 197 nm, 7 N, and 120 Pa, respectively). Microscopy of the LAX gels showed linked strands, while the system was less connected in the PAX gels. The Raman band at 2895 cm-1 of the LAX and PAX gels was less intense, indicating enhanced hydrogen bonding compared to that of AX. This decrease was less dramatic for the PAX gels. The greater content of 5,5'-diferulic acid in PAX gels could favor intrachain bonds, affecting their rheological, structural, and spectroscopic characteristics. Laccase may be a better option than peroxidase for AX gelation intended for food and biotechnological applications.

The effect of thiamine-coating nanoparticles on their biodistribution and fate following oral administration.

Thiamine-coated nanoparticles were prepared by two different preparative methods and evaluated to compare their mucus-penetrating properties and fate in vivo. The first method of preparation consisted of surface modification of freshly poly(anhydride) nanoparticles (NP) by simple incubation with thiamine (T-NPA). The second procedure focused on the preparation and characterization of a new polymeric conjugate between the poly(anhydride) backbone and thiamine prior the nanoparticle formation (T-NPB). The resulting nanoparticles displayed comparable sizes (about 200 nm) and slightly negative surface charges. For T-NPA, the amount of thiamine associated to the surface of the nanoparticles was 15 µg/mg. For in vivo studies, nanoparticles were labelled with either 99mTc or Lumogen® Red. T-NPA and T-NPB moved faster from the stomach to the small intestine than naked nanoparticles. Two hours post-administration, for T-NPA and T-NPB, >30% of the given dose was found in close contact with the intestinal mucosa, compared with a 13.5% for NP. Interestingly, both types of thiamine-coated nanoparticles showed a greater ability to cross the mucus layer and interact with the surface of the intestinal epithelium than NP, which remained adhered in the mucus layer. Four hours post-administration, around 35% of T-NPA and T-NPB were localized in the ileum of animals. Overall, both preparative processes yielded thiamine decorated carriers with similar physico-chemical and biodistribution properties, increasing the versatility of these nanocarriers as oral delivery systems for a number of biologically active compounds.

In vitro degradation of covalently cross-linked arabinoxylan hydrogels by bifidobacteria.

Arabinoxylan gels with different cross-linking densities, swelling ratios, and rheological properties were obtained by increasing the concentration of arabinoxylan from 4 to 6% (w/v) during oxidative gelation by laccase. The degradation of these covalently cross-linked gels by a mixture of two Bifidobacterium strains (Bifidobacterium longum and Bifidobacterium adolescentis) was investigated. The kinetics of the evolution of structural morphology of the arabinoxylan gel, the carbohydrate utilization profiles and the bacterial production of short-acid fatty acid (SCFA) were measured. Scanning electron microscopy analysis of the degraded gels showed multiple cavity structures resulting from the bacterial action. The total SCFA decreased when the degree of cross-linking increased in the gels. A slower fermentation of arabinoxylan chains was obtained for arabinoxylan gels with more dense network structures. These results suggest that the differences in the structural features and properties studied in this work affect the degradation time of the arabinoxylan gels.

Entrapment of probiotics in water extractable arabinoxylan gels: rheological and microstructural characterization.

Due to their porous structure, aqueous environment and dietary fiber nature arabinoxylan (AX) gels could have potential applications for colon-specific therapeutic molecule delivery. In addition, prebiotic and health related effects of AX have been previously demonstrated. It has been also reported that cross-linked AX can be degraded by bacteria from the intestinal microbiota. However, AX gels have not been abundantly studied as carrier systems and there is no information available concerning their capability to entrap cells. In this regard, probiotic bacteria such as Bifidobacterium longum have been the focus of intense research activity lately. The objective of this research was to investigate the entrapment of probiotic B. longum in AX gels. AX solution at 2% (w/v) containing B. longum (1 × 107 CFU/cm) formed gels induced by laccase as cross-linking agent. The entrapment of B. longum decreased gel elasticity from 31 to 23 Pa, probably by affecting the physical interactions taking place between WEAX chains. Images of AX gels containing B. longum viewed under a scanning electron microscope show the gel network with the bacterial cells entrapped inside. The microstructure of these gels resembles that of an imperfect honeycomb. The results suggest that AX gels can be potential candidates for the entrapment of probiotics.

Arabinoxylan microspheres: structural and textural characteristics.

The aim of this research was to study the structural and textural characteristics of maize bran arabinoxylan (MBAX) microspheres. The laccase-induced cross-linking process was monitored by storage (G') and loss (G'') moduli changes in a 4% (w/v) MBAX solution. The G' and G'' values at the plateau region were 215 and 4 Pa, respectively. After gelation, the content of ferulic acid dimers decreased from 0.135 to 0.03 µg/mg MBAX, suggesting the formation of ferulated structures unreleased by mild alkaline hydrolysis. MBAX microspheres presented an average diameter of 531 µm and a swelling ratio value (q) of 18 g water/g MBAX. The structural parameters of MBAX microspheres were calculated from equilibrium swelling experiments, presenting an average mesh size of 52 nm. Microstructure and textural properties of dried MBAX microspheres were studied by scanning electron microscopy and nitrogen adsorption/desorption isotherms, respectively, showing a heterogeneous mesoporous and macroporous structure throughout the network.

The peroxidase/H2O2 system as a free radical-generating agent for gelling maize bran arabinoxylans: rheological and structural properties.

The oxidative gelation of maize bran arabinoxylans (MBAX) using a peroxidase/H(2)O(2) system as a free radical-generating agent was investigated. The peroxidase/H(2)O(2) system led to the formation of dimers and trimer of ferulic acid as covalent cross-link structures in the MBAX network. MBAX gels at 4% (w/v) presented a storage modulus of 180 Pa. The structural parameters of MBAX gels were calculated from swelling experiments. MBAX gels presented a molecular weight between two cross-links (Mc), a cross-linking density (ρ(c)) and a mesh size (x) of 49 × 103 g/mol, 30 × 10-6 mol/cm3 and 193 nm, respectively.