The biology of mucus: Composition, synthesis and organization

Liquid-liquid phase transitions and amyloid aggregation in proteins related to cancer and neurodegenerative diseases

Liquid-liquid phase separation (LLPS) and phase transition (LLPT) of proteins and nucleic acids have emerged as a new paradigm in cell biology. Here we will describe the recent findings about LLPS and LLPT, including the molecular and physical determinants leading to their formation, the resulting functions and their implications in cell physiology and disease. Amyloid aggregation is implicated in many neurodegenerative diseases and cancer, and LLPS of proteins involved in these diseases appear to be related to their function in different cell contexts. Amyloid formation would correspond to an irreversible liquid-to-solid transition, as clearly observed in the case of PrP, TDP43, FUS/TLS and tau protein in neurodegenerative pathologies as well as with the mutant tumor suppressor p53 in cancer. Nucleic acids play a modulatory effect on both LLPS and amyloid aggregation. Understanding the molecular events regulating how the demixing process advances to solid-like fibril materials is crucial for the development of novel therapeutic strategies against cancer and neurodegenerative maladies.

Docosahexaenoic and Eicosapentaenoic Acids Prevent Altered-Muc2 Secretion Induced by Palmitic Acid by Alleviating Endoplasmic Reticulum Stress in LS174T Goblet Cells

Diets high in saturated fatty acids (FA) represent a risk factor for the development of obesity and associated metabolic disorders, partly through their impact on the epithelial cell barrier integrity. We hypothesized that unsaturated FA could alleviate saturated FA-induced endoplasmic reticulum (ER) stress occurring in intestinal secretory goblet cells, and consequently the reduced synthesis and secretion of mucins that form the protective mucus barrier. To investigate this hypothesis, we treated well-differentiated human colonic LS174T goblet cells with palmitic acid (PAL)—the most commonly used inducer of lipotoxicity in in vitro systems—or n-9, n-6, or n-3 unsaturated fatty acids alone or in co-treatment with PAL, and measured the impact of such treatments on ER stress and Muc2 production. Our results showed that only eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids protect goblet cells against ER stress-mediated altered Muc2 secretion induced by PAL, whereas neither linolenic acid nor n-9 and n-6 FA are able to provide such protection. We conclude that EPA and DHA could represent potential therapeutic nutrients against the detrimental lipotoxicity of saturated fatty acids, associated with type 2 diabetes and obesity or inflammatory bowel disease. These in vitro data remain to be explored in vivo in a context of dietary obesity.

The impact of apical and basolateral albumin on intestinal zinc resorption in the Caco-2/HT-29-MTX co-culture model

The molecular mechanisms of intestinal zinc resorption and its regulation are still topics of ongoing research. To this end, the application of suitable in vitro intestinal models, optimized with regard to their cellular composition and medium constituents, is of crucial importance. As one vital aspect, the impact of cell culture media or buffer compounds, respectively, on the speciation and cellular availability of zinc has to be considered when investigating zinc resorption. Thus, the present study aims to investigate the impact of serum, and in particular its main constituent serum albumin, on zinc uptake and toxicity in the intestinal cell line Caco-2. Furthermore, the impact of serum albumin on zinc resorption is analyzed using a co-culture of Caco-2 cells and the mucin-producing goblet cell line HT-29-MTX. Apically added albumin significantly impaired zinc uptake into enterocytes and buffered its cytotoxicity. Yet, undigested albumin does not occur in the intestinal lumen in vivo and impairment of zinc uptake was abrogated by digestion of albumin. Interestingly, zinc uptake, as well as gene expression studies of mt1a and selected intestinal zinc transporters after zinc incubation for 24 h, did not show significant differences between 0 and 10% serum. Importantly, the basolateral application of serum in a transport study significantly enhanced fractional apical zinc resorption, suggesting that the occurrence of a zinc acceptor in the plasma considerably affects intestinal zinc resorption. This study demonstrates that the apical and basolateral medium composition is crucial when investigating zinc, particularly its intestinal resorption, using in vitro cell culture.

Fourier transform infrared spectroscopic imaging of colon tissues: evaluating the significance of amide I and C-H stretching bands in diagnostic applications with machine learning

Fourier transform infrared (FTIR) spectroscopic imaging of colon biopsy tissues in transmission combined with machine learning for the classification of different stages of colon malignancy was carried out in this study. Two different approaches, an optical and a computational one, were applied for the elimination of the scattering background during the measurements and compared with the results of the machine learning model without correction for the scattering. Several different data processing pathways were implemented in order to obtain a high accuracy of the prediction model. This study demonstrates, for the first time, that C-H stretching and amide I bands are of little to no significance in the classification of the colon malignancy, based on the Gini importance values by random forest (RF). The best prediction outcome is found when supervised RF classification was carried out in the fingerprint region of the spectral data between 1500 and 1000 cm^-1 (excluding the contribution of amide I and II bands). An overall prediction accuracy higher than 90% is achieved through the RF. The results also show that dysplastic and hyperplastic tissues are well distinguished. This leads to the insight that the important differences between hyperplastic and dysplastic colon tissues lie within the fingerprint region of FTIR spectra. In this study, computational correction performed better than optical correction, but the findings show that the disease states of colon biopsies can be distinguished effectively without elimination of Mie scattering effect. Graphical abstract.

A microrobotic system guided by photoacoustic computed tomography for targeted navigation in intestines in vivo

Recently, tremendous progress in synthetic micro/nanomotors in diverse environment has been made for potential biomedical applications. However, existing micro/nanomotor platforms are inefficient for deep tissue imaging and motion control in vivo. Here, we present a photoacoustic computed tomography (PACT) guided investigation of micromotors in intestines in vivo. The micromotors enveloped in microcapsules are stable in the stomach and exhibit efficient propulsion in various biofluids once released. The migration of micromotor capsules toward the targeted regions in intestines has been visualized by PACT in real time in vivo. Near-infrared light irradiation induces disintegration of the capsules to release the cargo-loaded micromotors. The intensive propulsion of the micromotors effectively prolongs the retention in intestines. The integration of the newly developed microrobotic system and PACT enables deep imaging and precise control of the micromotors in vivo and promises practical biomedical applications, such as drug delivery.

Progress and Current Trends in the Synthesis of Novel Polymers with Enhanced Mucoadhesive Properties

Mucoadhesion is defined as the adherence of a synthetic or natural polymer to a mucosal membrane via physical or chemical interactions. Mucoadhesive materials are widely used to develop dosage forms for transmucosal drug delivery via ocular, nasal, esophageal, oral, vaginal, rectal, and intravesical routes of administration. This review will discuss some of the most prominent and recent synthetic methodologies employed to modify polymeric materials in order to enhance their mucoadhesive properties. This includes chemical conjugation of polymers with molecules bearing thiol-, catechol-, boronate-, acrylate-, methacrylate-, maleimide-, and N-hydroxy(sulfo)succinimide ester- groups.

Gastroduodenal Injury: Role of Protective Factors

PURPOSE OF REVIEW

The gastroduodenal mucosal layer is a complex and dynamic system that functions in an interdependent manner to resist injury. We review and summarize the most updated knowledge about gastroduodenal defense mechanisms and specifically address (a) the mucous barrier, (b) membrane and cellular properties, and vascular, hormonal, and (c) gaseous mediators.

RECENT FINDINGS

Trefoil factor family peptides play a crucial role in cellular restitution by increasing cellular permeability and expression of aquaporin channels, aiding cellular migration and tissue repair. Additionally, evidence suggests that the symptoms of functional dyspepsia may be attributed to alterations in the duodenum, including low-grade inflammation and increased mucosal permeability. The interaction of the various mucosal protective components helps maintain structural and functional homeostasis. There is increasing evidence suggesting that the upper GI microbiota plays a crucial role in the defense mechanisms. However, this warrants further investigation.

First Insight on the Mucus of the Annelid Myxicola infundibulum (Polychaeta, Sabellidae) as a Potential Prospect for Drug Discovery

Many marine organisms, including invertebrates, produce mucosal matrices having different functions. Besides mechanical protection, the mucus of many invertebrates contains specific compounds to make the animal poisonous and/or distasteful or irritating. The presence of antibiotic molecules is more advantageous for some invertebrates to contrast bacterial attack. In the present study we investigated the mucus of the Mediterranean annelid species Myxicola infundibulum living in a gelatinous envelope made up of dense mucus. Antimicrobial lysozyme-like and antioxidant activities were investigated to highlight the potential interest of the worm mucus as a source of bioactive compounds for biotechnological applications. In order to understand which kind of compounds could be responsible for the detected activities, the mucus of M. infundibulum was chemically characterized in terms of elemental composition, protein, lipid and carbohydrate content. Further chemical characterization was achieved by the advanced analytical technique of multinuclear and multidimensional NMR spectroscopy. NMR spectroscopy revealed the scarcity of lipids which preferentially resulted of alcoholic origin, or otherwise hydroxylate and several aminoacids (valine, leucine and alanine) in the aqueous extract in relation to the protein nature of M. infundibulum mucus. The mucus indeed is mainly composed by water (94% ± 0.7%) whereas its dry weight is made of proteins (36% ± 2.3%) followed by lipids (2.9% ± 0.07%) and carbohydrates (2% ± 0.31%). The mucus exerted a natural antibacterial lysozyme-like activity corresponding to 1.14 mg mL-1 of hen egg-white lysozyme and an antioxidant activity corresponding to 483.00 ± 79.22 nmolTE (Trolox equivalent)/mL sample as Trolox Equivalent Antioxidant Capacity (TEAC) and 276.26 ± 50.76 nmolTE/mL sample as Oxygen Radical Absorbance Capacity (ORAC). Therefore, our findings have potential implications due to the ongoing explosion of antibiotic resistant infections and the need to discover antibacterial agents. Additionally, the observed antioxidant activity is intriguing taking into account the need to find natural antioxidants useful for human health.

Mechanical shear controls bacterial penetration in mucus

Mucus plays crucial roles in higher organisms, from aiding fertilization to protecting the female reproductive tract. Here, we investigate how anisotropic organization of mucus affects bacterial motility. We demonstrate by cryo electron micrographs and elongated tracer particles imaging, that mucus anisotropy and heterogeneity depend on how mechanical stress is applied. In shallow mucus films, we observe bacteria reversing their swimming direction without U-turns. During the forward motion, bacteria burrowed tunnels that last for several seconds and enable them to swim back faster, following the same track. We elucidate the physical mechanism of direction reversal by fluorescent visualization of the flagella: when the bacterial body is suddenly stopped by the mucus structure, the compression on the flagellar bundle causes buckling, disassembly and reorganization on the other side of the bacterium. Our results shed light into motility of bacteria in complex visco-elastic fluids and can provide clues in the propagation of bacteria-born diseases in mucus.

Experimental models to study intestinal microbes–mucus interactions in health and disease

A close symbiotic relationship exists between the intestinal microbiota and its host. A critical component of gut homeostasis is the presence of a mucus layer covering the gastrointestinal tract. Mucus is a viscoelastic gel at the interface between the luminal content and the host tissue that provides a habitat to the gut microbiota and protects the intestinal epithelium. The review starts by setting up the biological context underpinning the need for experimental models to study gut bacteria-mucus interactions in the digestive environment. We provide an overview of the structure and function of intestinal mucus and mucins, their interactions with intestinal bacteria (including commensal, probiotics and pathogenic microorganisms) and their role in modulating health and disease states. We then describe the characteristics and potentials of experimental models currently available to study the mechanisms underpinning the interaction of mucus with gut microbes, including in vitro, ex vivo and in vivo models. We then discuss the limitations and challenges facing this field of research.

Novel aroylated phenylenediamine compounds enhance antimicrobial defense and maintain airway epithelial barrier integrity

Aroylated phenylenediamines (APDs) are novel inducers of innate immunity enhancing cathelicidin gene expression in human bronchial epithelial cell lines. Here we present two newly developed APDs and aimed at defining the response and signaling pathways for these compounds with reference to innate immunity and antimicrobial peptide (AMP) expression. Induction was initially defined with respect to dose and time and compared with the APD Entinostat (MS-275). The induction applies to several innate immunity effectors, indicating that APDs trigger a broad spectrum of antimicrobial responses. The bactericidal effect was shown in an infection model against Pseudomonas aeruginosa by estimating bacteria entering cells. Treatment with a selected APD counteracted Pseudomonas mediated disruption of epithelial integrity. This double action by inducing AMPs and enhancing epithelial integrity for one APD compound is unique and taken as a positive indication for host directed therapy (HDT). The APD effects are mediated through Signal transducer and activator of transcription 3 (STAT3) activation. Utilization of induced innate immunity to fight infections can reduce antibiotic usage, might be effective against multidrug resistant bacteria and is in line with improved stewardship in healthcare.

Interaction Between Chitosan and Mucin: Fundamentals and Applications

The term chitosan (CS) refers to a family of aminopolysaccharides derived from chitin. Among other properties, CS is nontoxic, mucoadhesive and can be used for load and transport drugs. Given these and other physicochemical and biological properties, CS is an optimal biopolymer for the development of transmucosal drug delivery systems, as well as for the treatment of pathologies related to mucosal dysfunctions. Mucins are glycoprotein macromolecules that are the major components of mucus overlaying epithelia. CS interacts with mucin and adsorbs on and changes the rheology of mucus. However, CS and mucins denote families of polymers/macromolecules with highly variable chemical structure, properties, and behavior. To date, their interactions at the molecular level have not been completely unraveled. Also, the properties of complexes composed of CS and mucin vary as a function of the sources and preparation of the polymers. As a consequence, the mucoadhesion and drug delivery properties of such complexes vary as well. The breadth of this review is on the molecular interactions between CS and mucin. In particular, in vitro and ex vivo characterization methods to investigate both the interactions at play during the formation of CS-mucin complexes, and the advances on the use of CS for transmucosal drug delivery are addressed.

Robust antigen-specific tuning of the nanoscale barrier properties of biogels using matrix-associating IgG and IgM antibodies

Biological hydrogels (biogels) are selective barriers that restrict passage of harmful substances yet allow the rapid movement of nutrients and select cells. Current methods to modulate the barrier properties of biogels typically involve bulk changes in order to restrict diffusion by either steric hindrance or direct high-affinity interactions with microstructural constituents. Here, we introduce a third mechanism, based on antibody-based third party anchors that bind specific foreign species but form only weak and transient bonds with biogel constituents. The weak affinity to biogel constituents allows antibody anchors to quickly accumulate on the surface of specific foreign species and facilitates immobilization via multiple crosslinks with the biogel matrix. Using the basement membrane Matrigel® and a mixture of laminin/entactin, we demonstrate that antigen-specific, but not control, IgG and IgM efficiently immobilize a variety of individual nanoparticles. The addition of Salmonella typhimurium-binding IgG to biogel markedly reduced the invasion of these highly motile bacteria. These results underscore a generalized strategy through which the barrier properties of biogels can be readily tuned with molecular specificity against a diverse array of particulates. STATEMENT OF SIGNIFICANCE: Biological hydrogels (biogels) are essential in living systems to control the movement of cells and unwanted substances. However, current methods to control transport within biogels rely on altering the microstructure of the biogel matrix at a gross level, either by reducing the pore size to restrict passage through steric hindrance or by chemically modifying the matrix itself. Both methods are either nonspecific or not scalable. Here, we offer a new approach, based on weakly adhesive third-party molecular anchors, that allow for a variety of foreign entities to be trapped within a biogel simultaneously with exceptional potency and molecular specificity, without perturbing the bulk properties of the biogel. This strategy greatly increases our ability to control the properties of biogels at the nanoscale, including those used for wound healing or tissue engineering applications.

Ultrastructural morphology of goblet cells of the conjunctiva of dogs

OBJECTIVE

To describe the morphology of goblet cells of the eyelid conjunctiva in dogs using transmission and scanning electron microscopy.

ANIMAL STUDIED

Ten dogs, both male and female of different breeds, with no ocular changes were examined (20 eyes).

PROCEDURES

Ten samples of conjunctiva were collected and processed for scanning and transmission electron microscopy (SEM and TEM), while another 10 samples were stained with Schiff's periodic stain (SPA) and alcian blue, pH 2.5, and analyzed using light microscopy.

RESULTS

Scanning electron microscopy revealed several points of mucus extrusion in the free apical portion of the goblet cells as well as a wide distribution of lymphoid follicles and macrophages intermingling with the microvilli of palpebral epithelium cells. TEM revealed normal goblet cells that were predominantly oval with wide cytoplasm of different diameters, and large vesicles with heterogeneous granules and free edges, suggesting the release of mucus content onto the conjunctival surface. Cytoplasmic organelles, such as the Golgi apparatus, endoplasmic reticulum, and a high number of mitochondria were also observed. All the samples were positive for SPA and alcian blue staining.

CONCLUSION

This is the first study to evaluate the goblet cells of the eyelid conjunctiva in healthy dogs using electron microscopy techniques. These results are useful for comparing the palpebral conjunctiva of dogs without ocular changes to palpebral conjunctiva of dogs and other species with ocular changes.

Challenges and Recent Progress in Oral Drug Delivery Systems for Biopharmaceuticals

Routes of drug administration and the corresponding physicochemical characteristics of a given route play significant roles in therapeutic efficacy and short term/long term biological effects. Each delivery method has favorable aspects and limitations, each requiring a specific delivery vehicles design. Among various routes, oral delivery has been recognized as the most attractive method, mainly due to its potential for solid formulations with long shelf life, sustained delivery, ease of administration and intensified immune response. At the same time, a few challenges exist in oral delivery, which have been the main research focus in the field in the past few years. The present work concisely reviews different administration routes as well as the advantages and disadvantages of each method, highlighting why oral delivery is currently the most promising approach. Subsequently, the present work discusses the main obstacles for oral systems and explains the most recent solutions proposed to deal with each issue.

Mucin adsorption on vaterite CaCO3 microcrystals for the prediction of mucoadhesive properties

Porous vaterite CaCO₃ crystals are widely used as containers for drug loading and as sacrificial templates to assemble polymer-based nano- and micro-particles at mild conditions. Special attention is paid nowadays to mucosal delivery where the glycoprotein mucin plays a crucial role as a main component of a mucous. In this work mucoadhesive properties of vaterite crystals have been tested by investigation of mucin binding to the crystals as a function of (i) time, (ii) glycoprotein concentration, (iii) adsorption conditions and (iv) degree of mucin desialization. Mucin adsorption follows Bangham equation indicating that diffusion into crystal pores is the rate-limiting step. Mucin strongly binds to the crystals (ΔG = -35 ± 4 kJ mol^-1) via electrostatic and hydrophobic interactions forming a gel and thus giving the tremendous mucin mass content in the crystals of up to 16%. Despite strong intermolecular mucin-mucin interactions, pure mucin spheres formed after crystal dissolution are unstable. However, introduction of protamine, actively used for mucosal delivery, makes the spheres stable via additional electrostatic bonding. The results of this work indicate that the vaterite crystals are extremely promising carriers for mucosal drug delivery and for development of test-systems for the analysis of the mucoadhesion.

Intestinal mucus is capable of stabilizing supersaturation of poorly water-soluble drugs

The utilization of polymers to stabilize drug supersaturation and enhance oral drug absorption has recently garnered considerable interest. The potential role of intestinal mucus in stabilizing drug supersaturation, however, has not been previously explored. The ability for intestinal mucus to stabilize drug supersaturation and delay drug precipitation is potentially useful in enhancing the absorption of orally dosed compounds from drug delivery systems that generate supersaturation within the gastrointestinal tract (e.g., solid dispersions, lipid-based drug delivery systems). This work aims to evaluate the precipitation-delaying abilities of intestinal mucus using carvedilol (CVDL) and piroxicam (PXM) as model drugs. In supersaturation-precipitation (S-P) experiments, CVDL and PXM supersaturation were induced in test media (0, 0.1, 0.2, 0.4%w/v mucin and 8%w/v native pig intestinal mucus (PIM)) via the solvent-shift method at supersaturation ratios (SSR) of 5 and 6, respectively. Time to drug precipitation was assessed using ion-selective electrodes and HPLC. The S-P experiments showed that increasing mucin concentration led to increasingly delayed CVDL precipitation, while PXM precipitation was prevented at all mucin concentrations studied. The ability of mucus-stabilized CVDL supersaturation to translate into enhanced CVDL absorption was evaluated in transport experiments using mucus-producing (90% Caco-2:10% HT29-MTX-E12 co-cultures) vs. non-mucus-producing intestinal monolayers (100% Caco-2 cultures). The absorption enhancement of CVDL (SSR = 5 relative to SSR = 1) was higher across mucus-producing than non-mucus-producing intestinal monolayers. This work demonstrates the potential for intestinal mucus to delay the precipitation and enhance the absorption of poorly water-soluble compounds, suggesting that drug supersaturation can be stabilized in close proximity to the absorptive site, thereby presenting a possible novel approach for targeted supersaturating drug delivery systems.

S-protected gellan gum: Decisive approach towards mucoadhesive antimicrobial vaginal films

The aim of this study was to synthesize novel polymeric excipients forming mucoadhesive films for treatment of vaginal microbial infections. 2-(2-Amino ethyldisulfanyl) nicotinic acid was conjugated with gellan gum via amide bond formation. The structure of the resulting S-protected gellan gum was confirmed by ¹H NMR. S-protected gellan gum variants were characterized for thiol content, cytotoxicity, rheological behaviour and film forming capability. Depending on the added amount of AMENA degree of thiolation was 81 ± 13 (S-GG 81) and 174 ± 16 (S-GG 174) μmol/g, respectively. Vaginal films were casted from S-protected gellan gum variants and studied for adherence to vaginal mucosa, drug release and antimicrobial activity. S-protected gellan gum remained biocompatible showing >87% cell viability. S-GG 81 and S-GG 174 exhibited 1.84- and 4.3-fold increased dynamic viscosity in porcine mucus in comparison to unmodified gellan gum, respectively. Compared to gellan gum films, thiol functionalized gellan gum films showed 3-fold improved adhesion on mucosal surface over a period of 3 h along with significant antimicrobial activity. Moreover, S-protected gellan gum provided a sustained release of metronidazole. According to these results, S-protected gellan gum proved to be a promising novel excipient for casting vaginal films, exhibiting strongly improved mucoadhesive and antimicrobial properties.

Viral nanoparticles can elude protein barriers: exploiting rather than imitating nature

Protein-corona formation in body fluids and/or entrapment of nanoparticles in protein matrices (e.g. food and mucus) can hinder the delivery of nanoparticles, irrespective of the route of administration. Here we demonstrate that certain viral nanoparticles (VNPs) can evade the adhesion of a broad panel of macromolecules from several biological milieus. We also show that the permeability of VNPs through mucin gels is far superior to that of synthetic nanoparticles. The non-sticky nature of VNPs implies that they will be able to readily cross most non-specific protein and glycoprotein barriers encountered, ubiquitously, upon administration through mucosal, and non-mucosal routes.

Methylmercury's chemistry: From the environment to the mammalian brain

Methylmercury is a neurotoxicant that is found in fish and rice. MeHg's toxicity is mediated by blockage of -SH and -SeH groups of proteins. However, the identification of MeHg's targets is elusive. Here we focus on the chemistry of MeHg in the abiotic and biotic environment. The toxicological chemistry of MeHg is complex in metazoans, but at the atomic level it can be explained by exchange reactions of MeHg bound to -S(e)H with another free -S(e)H group (R¹S(e)-HgMe + R²-S(e)H ↔ R¹S(e)H + R²-S(e)-HgMe). This reaction was first studied by professor Rabenstein and here it is referred as the "Rabenstein's Reaction". The absorption, distribution, and excretion of MeHg in the environment and in the body of animals will be dictated by Rabenstein's reactions. The affinity of MeHg by thiol and selenol groups and the exchange of MeHg by Rabenstein's Reaction (which is a diffusion controlled reaction) dictates MeHg's neurotoxicity. However, it is important to emphasize that the MeHg exchange reaction velocity with different types of thiol- and selenol-containing proteins will also depend on protein-specific structural and thermodynamical factors. New experimental approaches and detailed studies about the Rabenstein's reaction between MeHg with low molecular mass thiol (LMM-SH) molecules (cysteine, GSH, acetyl-CoA, lipoate, homocysteine) with abundant high molecular mass thiol (HMM-SH) molecules (albumin, hemoglobin) and HMM-SeH (GPxs, Selenoprotein P, TrxR1-3) are needed. The study of MeHg migration from -S(e)-Hg- bonds to free -S(e)H groups (Rabenstein's Reaction) in pure chemical systems and neural cells (with special emphasis to the LMM-SH and HMM-S(e)H molecules cited above) will be critical to developing realistic constants to be used in silico models that will predict the distribution of MeHg in humans.

Open and clean: the healthy nose

The nose exerts many functions, mainly for the respiration and the olfaction and represents the first doorway for the oxygen, but also for pathogens. The present Supplement reports some clinical experiences concerning the use of a new internal nasal dilator in different settings, including nasal obstructive disorders, obstructive sleep apnea syndrome, continuous positive active pressure (CPAP), and sport activity. The outcomes support the concept that a healthy nose should be maintained ever patent and free from secretions, as impaired nasal function can significantly affect quality of life. Therefore, an “open and clean nose” contributes in a relevant way to the subjective wellness. (www.actabiomedica.it)

Transparent Copper-Based Antibacterial Coatings with Enhanced Efficacy against Pseudomonas aeruginosa

Bacterial surface contamination is a major cause of hospital-associated infections. Antibacterial coatings can play an important role in reducing bacterial transmission via inanimate surfaces in healthcare settings. In this work, transparent copper-based antibacterial coatings were fabricated on commercial poly(vinyl fluoride) and stainless steel. Acrylated quaternized chitosan and ethylenediaminetetraacetic acid were covalently grafted on the substrate for complexation with copper ions. The number of viable Staphylococcus aureus in a droplet [containing ∼10⁴ colony forming units (CFU)], deposited on the copper-containing coating decreased by ∼96% within 60 min at 25 °C. With Pseudomonas aeruginosa, one of the most virulent and hardest to kill bacteria, no CFU could be observed within the same time span (killing efficacy >99.8% based on the detection limit). An increase in copper release from the coating was observed in the presence of P. aeruginosa, which was postulated to be due to the proteolytic activity of P. aeruginosa. The higher efficacy of the coating against P. aeruginosa compared to S. aureus is thus attributed to this increased copper release from the coating, which resulted in extensive bacterial membrane damage and death. The copper-containing coating on poly(vinyl fluoride) retained its antibacterial efficacy after 100 wipes with a water-wetted cloth or isopropanol wipes, demonstrating its durability and long-term efficacy. The coating did not exhibit significant cytotoxicity toward mammalian fibroblasts, further demonstrating its potential for mitigating bacterial transmission in a clinical setting.

High fish density delays wound healing in Atlantic salmon (Salmo salar)

In this study, we look closer at how high fish densities influence wound repair mechanisms in post-smolt Atlantic salmon. The fish were wounded with a 5 mm skin punch biopsy needle and stocked at two different densities, a high fish density (100 kg/m³) treatment and a low fish density treatment (20 kg/m³) serving as the control. The healing wounds were followed for 57 days with samples taken 1, 3, 7, 14, 36, 43 and 57 days post wounding. The transcriptomic analysis suggests that high fish density enhance inflammation and represses cell proliferation, tissue secretion and collagen synthesis in the healing wounds. The histological analysis further showed delayed epidermal and dermal repair in the high fish density treatment compared to control. The overall wound contraction was also altered by the treatment. In conclusion, high fish density enhances immune responses and delay tissue repair, which ultimately results in delayed wound healing.

Mucins and Their Role in Shaping the Functions of Mucus Barriers

We review what is currently understood about how the structure of the primary solid component of mucus, the glycoprotein mucin, gives rise to the mechanical and biochemical properties of mucus that are required for it to perform its diverse physiological roles. Macroscale processes such as lubrication require mucus of a certain stiffness and spinnability, which are set by structural features of the mucin network, including the identity and density of cross-links and the degree of glycosylation. At the microscale, these same features affect the mechanical environment experienced by small particles and play a crucial role in establishing an interaction-based filter. Finally, mucin glycans are critical for regulating microbial interactions, serving as receptor binding sites for adhesion, as nutrient sources, and as environmental signals. We conclude by discussing how these structural principles can be used in the design of synthetic mucin-mimetic materials and provide suggestions for directions of future work in this field.

In Vitro Studies on Zinc Binding and Buffering by Intestinal Mucins

The investigation of luminal factors influencing zinc availability and accessibility in the intestine is of great interest when analyzing parameters regulating intestinal zinc resorption. Of note, intestinal mucins were suggested to play a beneficial role in the luminal availability of zinc. Their exact zinc binding properties, however, remain unknown and the impact of these glycoproteins on human intestinal zinc resorption has not been investigated in detail. Thus, the aim of this study is to elucidate the impact of intestinal mucins on luminal uptake of zinc into enterocytes and its transfer into the blood. In the present study, in vitro zinc binding properties of mucins were analyzed using commercially available porcine mucins and secreted mucins of the goblet cell line HT-29-MTX. The molecular zinc binding capacity and average zinc binding affinity of these glycoproteins demonstrates that mucins contain multiple zinc-binding sites with biologically relevant affinity within one mucin molecule. Zinc uptake into the enterocyte cell line Caco-2 was impaired by zinc-depleted mucins. Yet this does not represent their form in the intestinal lumen in vivo under zinc adequate conditions. In fact, zinc-uptake studies into enterocytes in the presence of mucins with differing degree of zinc saturation revealed zinc buffering by these glycoproteins, indicating that mucin-bound zinc is still available for the cells. Finally, the impact of mucins on zinc resorption using three-dimensional cultures was studied comparing the zinc transfer of a Caco-2/HT-29-MTX co-culture and conventional Caco-2 monoculture. Here, the mucin secreting co-cultures yielded higher fractional zinc resorption and elevated zinc transport rates, suggesting that intestinal mucins facilitate the zinc uptake into enterocytes and act as a zinc delivery system for the intestinal epithelium.

Utilization of Host-Derived Glycans by Intestinal Lactobacillus and Bifidobacterium Species

Members of the genus Lactobacillus are commonly found at the gastrointestinal tract and other mucosal surfaces of humans. This genus includes various species with a great number of potentially probiotic bacteria. Other often-used probiotic species belong to Bifidobacterium, a genus almost exclusively associated with the gut. As probiotics must survive and be metabolically active at their target sites, namely host mucosal surfaces, consumption of host-produced glycans is a key factor for their survival and activity. The ability to metabolize glycans such as human milk oligosaccharides (HMOs), glycosaminoglycans and the glycan moieties of glycoproteins and glycolipids found at the mucosal surfaces grants a competitive advantage to lactobacilli and bifidobacteria. The analyses of the great number of sequenced genomes from these bacteria have revealed that many of them encode a wide assortment of genes involved in the metabolism and transport of carbohydrates, including several glycoside hydrolases required for metabolizing the carbohydrate moieties of mucins and HMOs. Here, the current knowledge on the genetic mechanisms, known catabolic pathways and biochemical properties of enzymes involved in the utilization of host-produced glycans by lactobacilli and bifidobacteria will be summarized.

Influencing the adhesion properties and wettability of mucin protein films by variation of the environmental pH

Mucins, the main component of the mucus secretions of goblet and epithelial cells, are known for exhibiting a different behaviour in accordance with their surrounding environment (i.e. among others the environmental pH), which induces a drastic change in their measured mechanical properties. In this work, we have first employed Atomic Force Microscopy (AFM) in Force Spectroscopy mode to evaluate the adhesion of porcine mucin films at the nanoscale, and the changes caused in this particular factor by a pH variation between 7.0 and 4.0, both quite common values in biological conditions. Measurements also involved additional varying factors such as the indenting tip chemistry (hydrophobic vs hydrophilic), its residence time on the measured film (0, 1 and/or 2 seconds), and increasing pulling rates (ranging from 0.1 up to 10 µm/s). A second approach regarded the macroscale behaviour of the films, due to their potential applicability in the development of a new set of stimuli-responsive biomaterials. This was possible by means of complementary Wilhelmy plate method (to test the wetting properties) and cell proliferation studies on films previously exposed to the corresponding pH solution. According to our results, treatment with lowest pH (4.0) provides porcine mucin with a more hydrophilic character, showing a much stronger adhesion for analogous chemistries, as well as enhanced capability for cell attachment and proliferation, which opens new pathways for their future use and consideration as scaffold-forming material.

Self-Assembled Mucin-Containing Microcarriers via Hard Templating on CaCO₃ Crystals

Porous vaterite crystals of CaCO₃ are extensively used for the fabrication of self-assembled polymer-based microparticles (capsules, beads, etc.) utilized for drug delivery and controlled release. The nature of the polymer used plays a crucial role and discovery of new perspective biopolymers is essential to assemble microparticles with desired characteristics, such as biocompatibility, drug loading efficiency/capacity, release rate, and stability. Glycoprotein mucin is tested here as a good candidate to assemble the microparticles because of high charge due to sialic acids, mucoadhesive properties, and a tendency to self-assemble, forming gels. Mucin loading into the crystals via co-synthesis is twice as effective as via adsorption into preformed crystals. Desialylated mucin has weaker binding to the crystals most probably due to electrostatic interactions between sialic acids and calcium ions on the crystal surface. Improved loading of low-molecular-weight inhibitor aprotinin into the mucin-containing crystals is demonstrated. Multilayer capsules (mucin/protamine)₃ have been made by the layer-by-layer self-assembly. Interestingly, the deposition of single mucin layers (mucin/water)₃ has also been proven, however, the capsules were unstable, most probably due to additional (to hydrogen bonding) electrostatic interactions in the case of the two polymers used. Finally, approaches to load biologically-active compounds (BACs) into the mucin-containing microparticles are discussed.

Role of mucins in lung homeostasis: regulated expression and biosynthesis in health and disease

In humans and mice, the first line of innate defense against inhaled pathogens and particles in the respiratory tract is airway mucus. The primary solid components of the mucus layer are the mucins MUC5AC and MUC5B, polymeric glycoproteins whose changes in abundance and structure can dramatically affect airway defense. Accordingly, MUC5AC/Muc5ac and MUC5B/Muc5b are tightly regulated at a transcriptional level by tissue-specific transcription factors in homeostasis and in response to injurious and inflammatory triggers. In addition to modulated levels of mucin gene transcription, translational and post-translational biosynthetic processes also exert significant influence upon mucin function. Mucins are massive macromolecules with numerous functional domains that contribute to their structural composition and biophysical properties. Single MUC5AC and MUC5B apoproteins have molecular masses of >400 kDa, and von Willebrand factor D-like as well as other cysteine-rich domain segments contribute to mucin polymerization and flexibility, thus increasing apoprotein length and complexity. Additional domains serve as sites for O-glycosylation, which increase further mucin mass several-fold. Glycosylation is a defining process for mucins that is specific with respect to additions of glycans to mucin apoprotein backbones, and glycan additions influence the physical properties of the mucins via structural modifications as well as charge interactions. Ultimately, through their tight regulation and complex assembly, airway mucins follow the biological rule of 'form fits function' in that their structural organization influences their role in lung homeostatic mechanisms.

The Role of Mucin in the Toxicological Impact of Polystyrene Nanoparticles

The development of novel oral drug delivery systems is an expanding area of research and both new approaches for improving their efficacy and the investigation of their potential toxicological effect are crucial and should be performed in parallel. Polystyrene nanoparticles (NPs) have been used for the production of diagnostic and therapeutic nanosystems, are widely used in food packaging, and have also served as models for investigating NPs interactions with biological systems. The mucous gel layer that covers the epithelium of the gastrointestinal system is a complex barrier-exchange system that it is mainly constituted by mucin and it constitutes the first physical barrier encountered after ingestion. In this study, we aimed to investigate the effect of polystyrene NPs on mucin and its potential role during NP–cell interactions. For this purpose, we evaluated the interaction of polystyrene NPs with mucin in dispersion by dynamic light scattering and with a deposited layer of mucin using a quartz crystal microbalance with dissipation technology. Next, we measured cell viability and the apoptotic state of three enterocyte-like cell lines that differ in their ability to produce mucin, after their exposure to the NPs. Positive charged NPs showed the ability to strongly interact and aggregate mucin in our model. Positive NPs affected cell viability and induced apoptosis in all cell lines independently of their ability of produce mucin.

Intestinal Mucin Induces More Endocytosis but Less Transcytosis of Nanoparticles across Enterocytes by Triggering Nanoclustering and Strengthening the Retrograde Pathway

Mucus, which is secreted by the goblet cells of enterocytes, constitutes the first obstacle encountered for the intestinal absorption of nanomedicines. For decades, mucus has simply been regarded as a physical barrier that hinders the permeation and absorption of drugs, because of its high viscosity and reticular structure, whereas the interaction of mucus ingredients with nanomedicines is usually neglected. It is unclear whether glycoproteins, as the main components of mucus, interact with nanomedicines. We also do not know how the potential interaction affects the subsequent transportation of nanomedicines through the intestinal epithelium. In this study, mucin as the key element of mucus was investigated to characterize the interaction of nanomedicines with mucus. PEG-modified gold nanoparticles (PGNPs) were fabricated as model nanoparticles. Mucin was found to adhere to the nanoparticle surface to form a corona structure and induce the clustering of PGNPs by joining particles together, demonstrating the interaction between mucin and PGNPs. In addition, two intestinal epithelia, Caco-2 (non- mucus secretion) and HT-29 (high mucus secretion), were compared to evaluate the influence of mucin on the cellular interaction of PGNPs. Amazingly, mucin altered the trafficking characteristic of PGNPs in intestinal epithelium. Both in vitro and in vivo investigations demonstrated more nanoparticles being internalized by cells due to the mucin coverage. However, mucin induced a significant reduction in the transcytosis of PGNPs across epithelial monolayers. The mechanism exploration further revealed that the "more endocytosis but less transcytosis (MELT)" effect was mainly attributed to the strengthened retrograde pathway in which more PGNPs were transported to Golgi apparatus and exocytosed back to the apical but not the basolateral side of the epithelial monolayers. The "MELT" effect endowed mucin with duality in the nanoparticle transportation. Therefore, the rational regulation based on the "MELT" effect will provide new insight into overcoming the mucus obstacle as a barrier and enhancing the oral absorption rate of nanomedicines.