The biology of mucus: Composition, synthesis and organization

Magnetic wire active microrheology of human respiratory mucus

Mucus is a viscoelastic gel secreted by the pulmonary epithelium in the tracheobronchial region of the lungs. The coordinated beating of cilia moves mucus upwards towards the pharynx, removing inhaled pathogens and particles from the airways. The efficacy of this clearance mechanism depends primarily on the rheological properties of mucus. Here we use magnetic wire based microrheology to study the viscoelastic properties of human mucus collected from human bronchus tubes. The response of wires between 5 and 80 μm in length to a rotating magnetic field is monitored by optical time-lapse microscopy and analyzed using constitutive equations of rheology, including those of Maxwell and Kelvin-Voigt. The static shear viscosity and elastic modulus can be inferred from low frequency (3 × 10^-3-30 rad s^-1) measurements, leading to the evaluation of the mucin network relaxation time. This relaxation time is found to be widely distributed, from one to several hundred seconds. Mucus is identified as a viscoelastic liquid with an elastic modulus of 2.5 ± 0.5 Pa and a static viscosity of 100 ± 40 Pa s. Our work shows that beyond the established spatial variations in rheological properties due to microcavities, mucus exhibits secondary inhomogeneities associated with the relaxation time of the mucin network that may be important for its flow properties.

Tripartite relationship between gut microbiota, intestinal mucus and dietary fibers: towards preventive strategies against enteric infections

The human gut is inhabited by a large variety of microorganims involved in many physiological processes and collectively referred as to gut microbiota. Disrupted microbiome has been associated with negative health outcomes and especially could promote the onset of enteric infections. To sustain their growth and persistence within the human digestive tract, gut microbes and enteric pathogens rely on two main polysaccharide compartments, namely dietary fibers and mucus carbohydrates. Several evidences suggest that the three-way relationship between gut microbiota, dietary fibers and mucus layer could unravel the capacity of enteric pathogens to colonise the human digestive tract and ultimately lead to infection. The review starts by shedding light on similarities and differences between dietary fibers and mucus carbohydrates structures and functions. Next, we provide an overview of the interactions of these two components with the third partner, namely, the gut microbiota, under health and disease situations. The review will then provide insights into the relevance of using dietary fibers interventions to prevent enteric infections with a focus on gut microbial imbalance and impaired-mucus integrity. Facing the numerous challenges in studying microbiota-pathogen-dietary fiber-mucus interactions, we lastly describe the characteristics and potentialities of currently available in vitro models of the human gut.

Vibrio cholerae motility in aquatic and mucus-mimicking environments

Cholera disease is caused by Vibrio cholerae infecting the lining of the small intestine and results in severe diarrhea. V. cholerae’s swimming motility is known to play a crucial role in pathogenicity and may aid the bacteria in crossing the intestinal mucus barrier to reach sites of infection, but the exact mechanisms are unknown. The cell can be either pushed or pulled by its single polar flagellum, but there is no consensus on the resulting repertoire of motility behaviors. We use high-throughput three-dimensional (3D) bacterial tracking to observe V. cholerae swimming in buffer, in viscous solutions of the synthetic polymer PVP, and in mucin solutions that may mimic the host environment. We perform a statistical characterization of its motility behavior on the basis of large 3D trajectory data sets. We find that V. cholerae performs asymmetric run-reverse-flick motility, consisting of a sequence of a forward run, reversal, and a shorter backward run, followed by a turn by approximately 90°, called a flick, preceding the next forward run. Unlike many run-reverse-flick swimmers, V. cholerae’s backward runs are much shorter than its forward runs, resulting in an increased effective diffusivity. We also find that the swimming speed is not constant but subject to frequent decreases. The turning frequency in mucin matches that observed in buffer. Run-reverse-flick motility and speed fluctuations are present in all environments studied, suggesting that these behaviors also occur in natural aquatic habitats as well as the host environment.

IMPORTANCE Cholera disease produces vomiting and severe diarrhea and causes approximately 100,000 deaths per year worldwide. The disease is caused by the bacterium Vibrio cholerae colonizing the lining of the small intestine. V. cholerae’s ability to swim is known to increase its infectivity, but the underlying mechanisms are not known. One possibility is that swimming aids in crossing the protective mucus barrier that covers the lining of the small intestine. Our work characterizing how V. cholerae swims in environments that mimic properties of the host environment may advance the understanding of how motility contributes to infection.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

The importance of pre-formulation studies and of 3D-printed nasal casts in the success of a pharmaceutical product intended for nose-to-brain delivery

This review aims to cement three hot topics in drug delivery: (a) the pre-formulation of new products intended for nose-to-brain delivery; (b) the development of nasal casts for studying the efficacy of potential new nose-to-brain delivery systems at the early of their development (pre-formulation); (c) the use of 3D printing based on a wide variety of materials (transparent, biocompatible, flexible) providing an unprecedented fabrication tool towards personalized medicine by printing nasal cast on-demand based on CT scans of patients. This review intends to show the links between these three subjects. Indeed, the pathway selected to administrate the drug to the brain not only influence the formulation strategies to implement but also the design of the cast, to get the most convincing measures from it. Moreover, the design of the cast himself influences the choice of the 3D-printing technology, which, in its turn, bring more constraints to the nasal replica design. Consequently, the formulation of the drug, the cast preparation and its realisation should be thought of as a whole and not separately.

Mucus

Mucus is a slimy hydrogel that lines the mucosal surfaces in our body, including the intestines, stomach, eyes, lungs and urogenital tract. This glycoprotein-rich network is truly the jack of all trades. As a barrier, it lubricates surfaces, protects our cells from physical stress, and selectively allows the passage of nutrients while clearing out pathogens and debris. As a home to our microbiota, it supports a level of microbial diversity that is unattainable with most culture methods. As a reservoir of complex carbohydrate structures called glycans, it plays critical roles in controlling cell adhesion and signaling, and it alters the behavior and spatial distribution of microbes. On top of all this, mucus regulates the passage of sperm during fertilization, heals wounds, helps us smell, and prevents the stomach from digesting itself, to name just a few of its functions. Given these impressive features, it is no wonder that mucus crosses boundaries of species and kingdoms - mucus gels are made by organisms ranging from the simplest metazoans to corals, snails, fish, and frogs. It is also no surprise that mucus is exploited in everyday applications, including foods, cosmetics, and other products relevant to medicine and industry.

Nutritional strategies for mucosal health: the interplay between microbes and mucin glycans

Many aspects of the mechanisms underlying the symbiosis between humans and gut microbes remain unknown and encompass some of the most intriguing questions in microbiome research. An important factor in this symbiosis is the interplay between microbes and human-produced glycans in mucin and breast milk. In this Opinion paper, I propose a synergy between the structural diversity of human mucin glycans and the enzymatic repertoire of the gut microbiome. The contribution of microbes to mucosal health is discussed, and the role of breast milk glycans in mucosal colonization by microbes is explained. The use of prebiotic mucin glycans in general, and specialized infant and medical nutrition in particular, should be considered as the field of interest to modulate the microbiota and improve mucosal health.

The role of the microbiome in gastrointestinal inflammation

The microbiome plays an important role in maintaining human health. Despite multiple factors being attributed to the shaping of the human microbiome, extrinsic factors such diet and use of medications including antibiotics appear to dominate. Mucosal surfaces, particularly in the gut, are highly adapted to be able to tolerate a large population of microorganisms whilst still being able to produce a rapid and effective immune response against infection. The intestinal microbiome is not functionally independent from the host mucosa and can, through presentation of microbe-associated molecular patterns (MAMPs) and generation of microbe-derived metabolites, fundamentally influence mucosal barrier integrity and modulate host immunity. In a healthy gut there is an abundance of beneficial bacteria that help to preserve intestinal homoeostasis, promote protective immune responses, and limit excessive inflammation. The importance of the microbiome is further highlighted during dysbiosis where a loss of this finely balanced microbial population can lead to mucosal barrier dysfunction, aberrant immune responses, and chronic inflammation that increases the risk of disease development. Improvements in our understanding of the microbiome are providing opportunities to harness members of a healthy microbiota to help reverse dysbiosis, reduce inflammation, and ultimately prevent disease progression.

Exogenous Polyamines Influence In Vitro Microbial Adhesion to Human Mucus According to the Age of Mucus Donor

Adhesion to intestinal mucus is the first step for microbiota colonization in early life. Polyamines are polycations with important physiological functions in both procaryotic and eucaryotic cells. However, their role in intestinal mucus adhesion is not known. The objective of the present study was to evaluate whether exogenous polyamines (putrescine, spermidine, spermine, and their combination) would alter the adhesive properties of Lacticaseibacillus rhamnosus GG (LGG), Bifidobacterium animalis subs. lactis Bb12, Cronobacter sakazakii, and Escherichia coli. Human intestinal mucus was isolated from healthy infants (0-6-month-old and 6-12-month-old) and healthy adults (25-52 years old). Spermidine significantly increased Bb12 adhesion (p < 0.05) in the mucus of infants (0-6 months) but reduced the adhesion of LGG in adult mucus (p < 0.05) with no significant effect in any of the infant groups. Spermine was more effective than polyamine combinations in reducing C. sakazakii (p < 0.05) adhesion in early infant mucus (0-6 months). The adhesion ability of E. coli remained unaffected by exogenous polyamines at any age in the concentrations tested. Our data suggest that polyamines may modulate the bacterial adhesion to mucus depending on the bacterial strain and depending at what age the mucus has been generated.

Oral lipid nanomedicines: Current status and future perspectives in cancer treatment

Oral anticancer drugs have earned a seat at the table, as the need for homecare treatment in oncology has increased. Interest in this field is growing as a result of their proven efficacy, lower costs and positive patient uptake. However, the gastrointestinal barrier is still the main obstacle to surmount in chemotherapeutic oral delivery. Anticancer nanomedicines have been proposed to solve this quandary. Among these, lipid nanoparticles are described to be efficiently absorbed while protecting drugs from early degradation in hostile environments. Their intestinal lymphatic tropism or mucoadhesive/penetrative properties give them unique characteristics for oral administration. Considering that chronic cancer cases are increasing over time, it is important to be able to provide treatments with low toxicity and low prices. The challenges, opportunities and therapeutic perspectives of lipid nanoparticles in this area will be discussed in this review, taking into consideration the pre-clinical and clinical progress made in the last decade.

Identification of mucin degraders of the human gut microbiota

Mucins are large glycoproteins consisting of approximately 80% of hetero-oligosaccharides. Gut mucin degraders of healthy subjects were investigated, through a culture dependent and independent approach. The faeces of five healthy adults were subjected to three steps of anaerobic enrichment in a medium with sole mucins as carbon and nitrogen sources. The bacterial community was compared before and after the enrichment by 16S rRNA gene profiling. Bacteria capable of fermenting sugars, such as Anaerotruncus, Holdemania, and Enterococcaceae likely took advantage of the carbohydrate chains. Escherichia coli and Enterobacteriaceae, Peptococcales, the Coriobacteriale Eggerthella, and a variety of Clostridia such as Oscillospiraceae, Anaerotruncus, and Lachnoclostridium, significantly increased and likely participated to the degradation of the protein backbone of mucin. The affinity of E. coli and Enterobacteriaceae for mucin may facilitate the access to the gut mucosa, promoting gut barrier damage and triggering systemic inflammatory responses. Only three species of strict anaerobes able to grow on mucin were isolated from the enrichments of five different microbiota: Clostridium disporicum, Clostridium tertium, and Paraclostridium benzoelyticum. The limited number of species isolated confirms that in the gut the degradation of these glycoproteins results from cooperation and cross-feeding among several species exhibiting different metabolic capabilities.

Nanosecond pulsed electric fields impair viability and mucin expression in mucinous colorectal carcinoma cell

Nanosecond pulsed electric fields (nsPEFs) are a non-thermal technology that can induce a myriad of biological responses and changes in cellular physiology. nsPEFs have gained significant attention as a novel cancer therapy. However, studies investigating the application of nsPEF in mucinous carcinomas are scarce. In this study, we explored several biological responses in two mucinous colorectal adenocarcinoma cell lines, LS 174T and HT-29, to nsPEF treatment. We determined the overall cell survival and viability rates following nsPEF treatment using CCK-8 and colony formation assays. We measured the intracellular effects of nsPEF treatment by analyzing cell cycle distribution, cell apoptosis and mitochondrial potential. We also analyzed mucin production at both mRNA and protein levels. Our results showed that nsPEF treatment significantly reduced mucinous cell viability in a dose-dependent manner. nsPEF treatment increased cell cycles arrest at G₀/G₁ while the proportion of G₂/M cells gradually decreased. Cell apoptosis increased following nsPEF treatment with a clear loss in mitochondrial membrane potential. Furthermore, the protein expression of functional mucin family members decreased after nsPEF treatment. In conclusion, nsPEF treatment reduced MCRC cell viability, cell proliferation, and mucin protein production while promoted apoptosis. Our work is a pilot study that projects some insights into the potential clinical applications of nsPEFs in treating mucinous colorectal carcinoma.

Slimy partners: the mucus barrier and gut microbiome in ulcerative colitis

Ulcerative colitis (UC) is a chronic recurrent intestinal inflammatory disease characterized by high incidence and young onset age. Recently, there have been some interesting findings in the pathogenesis of UC. The mucus barrier, which is composed of a mucin complex rich in O-glycosylation, not only provides nutrients and habitat for intestinal microbes but also orchestrates the taming of germs. In turn, the gut microbiota modulates the production and secretion of mucins and stratification of the mucus layers. Active bidirectional communication between the microbiota and its 'slimy' partner, the mucus barrier, seems to be a continually performed concerto, maintaining homeostasis of the gut ecological microenvironment. Any abnormalities may induce a disorder in the gut community, thereby causing inflammatory damage. Our review mainly focuses on the complicated communication between the mucus barrier and gut microbiome to explore a promising new avenue for UC therapy.

Chain stiffness boosts active nanoparticle transport in polymer networks

Recent advances in technologies such as nanomanufacturing and nanorobotics have opened new pathways for the design of active nanoparticles (NPs) capable of penetrating biolayers for biomedical applications, e.g., for drug delivery. The coupling and feedback between active NP motility (with large stochastic increments relative to passive NPs) and the induced nonequilibrium deformation and relaxation responses of the polymer network, spanning scales from the NP to the local structure of the network, remain to be clarified. Using molecular dynamics simulations, combined with a Rouse mode analysis of network chains and position and velocity autocorrelation functions of the NPs, we demonstrate that the mobility of active NPs within cross-linked, concentrated polymer networks is a monotonically increasing function of chain stiffness, contrary to passive NPs, for which chain stiffness suppresses mobility. In flexible networks, active NPs exhibit a behavior similar to passive NPs, with a boost in mobility proportional to the self-propulsion force. These results are suggestive of design strategies for active NP penetration of stiff biopolymer matrices.

Avoiding a Sticky Situation: Bypassing the Mucus Barrier for Improved Local Drug Delivery

The efficacy of drugs administered by traditional routes is limited by numerous biological barriers that preclude reaching the intended site of action. Further, full body systemic exposure leads to dose-limiting, off-target side effects. Topical formulations may provide more efficacious drug and nucleic acid delivery for diseases and conditions affecting mucosal tissues, but the mucus protecting our epithelial surfaces is a formidable barrier. Here, we describe recent advances in mucus-penetrating approaches for drug and nucleic acid delivery to the ocular surface, the female reproductive tract, the gastrointestinal tract, and the airways.

The Relationship between Mucins and Ulcerative Colitis: A Systematic Review

Mucins are a family of glycosylated proteins which are the primary constituents of mucus and play a dynamic role in the regulation of the protective mucosal barriers throughout the human body. Ulcerative colitis (UC) is an Inflammatory Bowel Disease (IBD) characterised by continuous inflammation of the inner layer of the large intestine, and in this systematic review we analyse currently available data to determine whether alterations exist in mucin activity in the colonic mucosa of UC patients. Database searches were conducted to identify studies published between 1990 and 2020 that assess the role of mucins in cohorts of UC patients, where biopsy specimens were resected for analysis and control groups were included for comparison. 5497 articles were initially identified and of these 14 studies were systematically selected for analysis, a further 2 articles were identified through citation chaining. Therefore, 16 studies were critically reviewed. 13 of these studies assessed the role of MUC2 in UC and the majority of articles indicated that alterations in MUC2 structure or synthesis had an impact on the colonic mucosa, although conflicting results were presented regarding MUC2 expression. This review highlights the importance of further research to enhance our understanding of mucin regulation in UC and summarises data that may inform future studies.

Transcriptomics and metabolomics reveal the adaption of Akkermansia muciniphila to high mucin by regulating energy homeostasis

In gut, Akkermansia muciniphila (A. muciniphila) probably exerts its probiotic activities by the positive modulation of mucus thickness and gut barrier integrity. However, the potential mechanisms between A. muciniphila and mucin balance have not been fully elucidated. In this study, we cultured the bacterium in a BHI medium containing 0% to 0.5% mucin, and transcriptome and gas chromatography mass spectrometry (GC-MS) analyses were performed. We found that 0.5% (m/v) mucin in a BHI medium induced 1191 microbial genes to be differentially expressed, and 49 metabolites to be changed. The metabolites of sorbose, mannose, 2,7-anhydro-β-sedoheptulose, fructose, phenylalanine, threonine, lysine, ornithine, asparagine, alanine and glutamic acid were decreased by 0.5% mucin, while the metabolites of leucine, valine and N-acetylneuraminic acid were increased. The association analysis between transcriptome and metabolome revealed that A. muciniphila gave strong responses to energy metabolism, amino sugar and nucleotide sugar metabolism, and galactose metabolism pathways to adapt to high mucin in the medium. This finding showed that only when mucin reached a certain concentration in a BHI medium, A. muciniphila could respond to the culture environment significantly at the level of genes and metabolites, and changed its metabolic characteristics by altering the effect on carbohydrates and amino acids.

A Dynamic, Supramolecular View on the Multivalent Interaction between Influenza Virus and Host Cell

Understanding how influenza viruses traverse the mucus and recognize host cells is critical for evaluating their zoonotic potential, and for prevention and treatment of the disease. The surface of the influenza A virus is covered with the receptor-binding protein hemagglutinin and the receptor-cleaving enzyme neuraminidase, which jointly control the interactions between the virus and the host cell. These proteins are organized in closely spaced trimers and tetramers to facilitate multivalent interactions with sialic acid-terminated glycans. This review shows that the individually weak multivalent interactions of influenza viruses allow superselective binding, virus-induced recruitment of receptors, and the formation of dynamic complexes that facilitate molecular walking. Techniques to measure the avidity and receptor specificity of influenza viruses are reviewed, and the pivotal role of multivalent interactions with their emergent properties in crossing the mucus and entering host cells is discussed. A model is proposed for the initiation of cell entry through virus-induced receptor clustering. The multivalent interactions of influenza viruses are maintained in a dynamic regime by a functional balance between binding and cleaving.

Current strategies for oral delivery of BCS IV drug nanocrystals: challenges, solutions and future trends

INTRODUCTION

Oral absorption of BCS IV drug benefits little from improved dissolution. Therefore, the absorption of BCS IV drug nanocrystals 'as a whole' strategy is preferred, and structural modification of nanocrystals is required. Surface modification helps the nanocrystals maintain particle structure before drug dissolution is needed, thus enhancing the oral absorption of BCS IV drugs and promoting therapeutic effect. Here, the main challenges and solutions of oral BCS IV drug nanocrystals delivery are discussed. Moreover, strategies for nanocrystal surface modification that facilitates oral bioavailability of BCS IV drugs are highlighted, and provide insights for the innovation in oral drug delivery.

AREAS COVERED

Promising size, shape, and surface modification of nanocrystals have gained interests for application in oral BCS IV drugs.

EXPERT OPINION

Nanocrystal surface modification is a feasible method to maintain the structural integrity of nanocrystals, and the introduced materials can also be modified to integrate additional functions to further facilitate the absorption of nanocrystals. It is expected that the absorption 'as a whole' strategy of nanocrystals will provide different choices for the oral BCS IV drugs.

Human Laryngeal Mucus from the Vocal Folds: Rheological Characterization by Particle Tracking Microrheology and Oscillatory Shear Rheology

Mucus consistency affects voice physiology and is connected to voice disorders. Nevertheless, the rheological characteristics of human laryngeal mucus from the vocal folds remain unknown. Knowledge about mucus viscoelasticity enables fabrication of artificial mucus with natural properties, more realistic ex-vivo experiments and promotes a better understanding and improved treatment of dysphonia with regard to mucus consistency. We studied human laryngeal mucus samples from the vocal folds with two complementary approaches: 19 samples were successfully applied to particle tracking microrheology (PTM) and five additional samples to oscillatory shear rheology (OSR). Mucus was collected by experienced laryngologists from patients together with demographic data. The analysis of the viscoelasticity revealed diversity among the investigated mucus samples according to their rigidity (absolute G′ and G″). Moreover some samples revealed throughout solid-like character (G′ > G″), whereas some underwent a change from solid-like to liquid-like (G′ < G″). This led to a subdivision into three groups. We assume that the reason for the differences is a variation in the hydration level of the mucus, which affects the mucin concentration and network formation factors of the mucin mesh. The demographic data could not be correlated to the differences, except for the smoking behavior. Mucus of predominant liquid-like character was associated with current smokers.

Recent Advancements in Polymer/Liposome Assembly for Drug Delivery: From Surface Modifications to Hybrid Vesicles

Liposomes are consolidated and attractive biomimetic nanocarriers widely used in the field of drug delivery. The structural versatility of liposomes has been exploited for the development of various carriers for the topical or systemic delivery of drugs and bioactive molecules, with the possibility of increasing their bioavailability and stability, and modulating and directing their release, while limiting the side effects at the same time. Nevertheless, first-generation vesicles suffer from some limitations including physical instability, short in vivo circulation lifetime, reduced payload, uncontrolled release properties, and low targeting abilities. Therefore, liposome preparation technology soon took advantage of the possibility of improving vesicle performance using both natural and synthetic polymers. Polymers can easily be synthesized in a controlled manner over a wide range of molecular weights and in a low dispersity range. Their properties are widely tunable and therefore allow the low chemical versatility typical of lipids to be overcome. Moreover, depending on their structure, polymers can be used to create a simple covering on the liposome surface or to intercalate in the phospholipid bilayer to give rise to real hybrid structures. This review illustrates the main strategies implemented in the field of polymer/liposome assembly for drug delivery, with a look at the most recent publications without neglecting basic concepts for a simple and complete understanding by the reader.

Long-term evolution of the epithelial cell secretome in preclinical 3D models of the human bronchial epithelium

The human bronchial epithelium is the first line of defense against atmospheric particles, pollutants, and respiratory pathogens such as the novel SARS-CoV-2. The epithelial cells form a tight barrier and secrete proteins that are major components of the mucosal immune response. Functional in vitro models of the human lung are essential for screening the epithelial response and assessing the toxicity and barrier crossing of drugs, inhaled particles, and pollutants. However, there is a lack of models to investigate the effect of chronic exposure without resorting to animal testing. Here, we developed a 3D model of the human bronchial epithelium using Calu-3 cell line and demonstrated its viability and functionality for 21 days without subculturing. We investigated the effect of reduced Fetal Bovine Serum supplementation in the basal medium and defined the minimal supplementation needed to maintain a functional epithelium, so that the amount of exogenous serum proteins could be reduced during drug testing. The long-term evolution of the epithelial cell secretome was fully characterized by quantitative mass spectrometry in two preclinical models using Calu-3 or primary NHBE cells. 408 common secreted proteins were identified while significant differences in protein abundance were observed with time, suggesting that 7-10 days are necessary to establish a mature secretome in the Calu-3 model. The associated Reactome pathways highlight the role of the secreted proteins in the immune response of the bronchial epithelium. We suggest this preclinical 3D model can be used to evaluate the long-term toxicity of drugs or particles on the human bronchial epithelium, and subsequently to investigate their effect on the epithelial cell secretions.

Structural Alterations of Mucins Are Associated with Losses in Functionality

Commercial mucin glycoproteins are routinely used as a model to investigate the broad range of important functions mucins fulfill in our bodies, including lubrication, protection against hostile germs, and the accommodation of a healthy microbiome. Moreover, purified mucins are increasingly selected as building blocks for multifunctional materials, i.e., as components of hydrogels or coatings. By performing a detailed side-by-side comparison of commercially available and lab-purified variants of porcine gastric mucins, we decipher key molecular motifs that are crucial for mucin functionality. As two main structural features, we identify the hydrophobic termini and the hydrophilic glycosylation pattern of the mucin glycoprotein; moreover, we describe how alterations in those structural motifs affect the different properties of mucins-on both microscopic and macroscopic levels. This study provides a detailed understanding of how distinct functionalities of gastric mucins are established, and it highlights the need for high-quality mucins-for both basic research and the development of mucin-based medical products.

Physiological activity of E. coli engineered to produce butyric acid

Faecalibacterium prausnitzii (F. prausnitzii) is one of the most abundant bacteria in the human intestine, with its anti‐inflammatory effects establishing it as a major effector in human intestinal health. However, its extreme sensitivity to oxygen makes its cultivation and physiological study difficult. F. prausnitzii produces butyric acid, which is beneficial to human gut health. Butyric acid is a short‐chain fatty acid (SCFA) produced by the fermentation of carbohydrates, such as dietary fibre in the large bowel. The genes encoding butyryl‐CoA dehydrogenase (BCD) and butyryl‐CoA:acetate CoA transferase (BUT) in F. prausnitzii were cloned and expressed in E. coli to determine the effect of butyric acid production on intestinal health using DSS‐induced colitis model mice. The results from the E. coli Nissle 1917 strain, expressing BCD, BUT, or both, showed that BCD was essential, while BUT was dispensable for producing butyric acid. The effects of different carbon sources, such as glucose, N‐acetylglucosamine (NAG), N‐acetylgalactosamine (NAGA), and inulin, were compared with results showing that the optimal carbon sources for butyric acid production were NAG, a major component of mucin in the human intestine, and glucose. Furthermore, the anti‐inflammatory effects of butyric acid production were tested by administering these strains to DSS‐induced colitis model mice. The oral administration of the E. coli Nissle 1917 strain, carrying the expression vector for BCD and BUT (EcN‐BCD‐BUT), was found to prevent DSS‐induced damage. Introduction of the BCD expression vector into E. coli Nissle 1917 led to increased butyric acid production, which improved the strain’s health‐beneficial effects.

The genus bifidobacterium: From genomics to functionality of an important component of the mammalian gut microbiota running title: Bifidobacterial adaptation to and interaction with the host

Members of the genus Bifidobacterium are dominant and symbiotic inhabitants of the mammalian gastrointestinal tract. Being vertically transmitted, bifidobacterial host colonization commences immediately after birth and leads to a phase of host infancy during which bifidobacteria are highly prevalent and abundant to then transit to a reduced, yet stable abundance phase during host adulthood. However, in order to reach and stably colonize their elective niche, i.e. the large intestine, bifidobacteria have to cope with a multitude of oxidative, osmotic and bile salt/acid stress challenges that occur along the gastrointestinal tract (GIT). Concurrently, bifidobacteria not only have to compete with the myriad of other gut commensals for nutrient acquisition, but they also require protection against bacterial viruses. In this context, Next-Generation Sequencing (NGS) techniques, allowing large-scale comparative and functional genome analyses have helped to identify the genetic strategies that bifidobacteria have developed in order to colonize, survive and adopt to the highly competitive mammalian gastrointestinal environment. The current review is aimed at providing a comprehensive overview concerning the molecular strategies on which bifidobacteria rely to stably and successfully colonize the mammalian gut.

Chitosan-based systems aimed at local application for vaginal infections

Vaginal administration is a promising route for the local treatment of infectious vaginal diseases since it can bypass the first-pass metabolism, drug interactions, and adverse effects. However, the commercial products currently available for topical vulvovaginal treatment have low acceptability and do not adequately explore this route. Mucoadhesive systems can optimize the efficacy of drugs administered by this route to increase the retention time of the drug in the vaginal environment. Several polymers are used to develop mucoadhesive systems, among them chitosan, a natural polymer that is highly biocompatible and technologically versatile. Thus, the present review aimed to analyze the studies that used chitosan to develop mucoadhesive systems for the treatment of local vaginal infections. These studies demonstrated that chitosan as a component of mucoadhesive drug delivery systems (DDS) is a promising device for the treatment of vaginal infectious diseases, due to the intrinsic antimicrobial activity of this biopolymer and because it does not interfere with the effectiveness of the drugs used for the treatment.

Home, sweet home: how mucus accommodates our microbiota

As a natural environment for human-microbiota interactions, healthy mucus houses a remarkably stable and diverse microbial community. Maintaining this microbiota is essential to human health, both to support the commensal bacteria that perform a wide array of beneficial functions and to prevent the outgrowth of pathogens. However, how the host selects and maintains a specialized microbiota remains largely unknown. In this viewpoint, we propose several strategies by which mucus may regulate the composition and function of the human microbiota and discuss how compromised mucus barriers in disease can give rise to microbial dysbiosis.

Exploring the Toxicity, Lung Distribution, and Cellular Uptake of Rifampicin and Ascorbic Acid-Loaded Alginate Nanoparticles as Therapeutic Treatment of Lung Intracellular Infections

Nanotechnology is a very promising technological tool to combat health problems associated with the loss of effectiveness of currently used antibiotics. Previously, we developed a formulation consisting of a chitosan and tween 80-decorated alginate nanocarrier that encapsulates rifampicin and the antioxidant ascorbic acid (RIF/ASC), intended for the treatment of respiratory intracellular infections. Here, we investigated the effects of RIF/ASC-loaded NPs on the respiratory mucus and the pulmonary surfactant. In addition, we evaluated their cytotoxicity for lung cells in vitro, and their biodistribution on rat lungs in vivo after their intratracheal administration. Findings herein demonstrated that RIF/ASC-loaded NPs display a favorable lung biocompatibility profile and a uniform distribution throughout lung lobules. RIF/ASC-loaded NPs were mainly uptaken by lung macrophages, their primary target. In summary, findings show that our novel designed RIF/ASC NPs could be a suitable system for antibiotic lung administration with promising perspectives for the treatment of pulmonary intracellular infections.

Models to evaluate the barrier properties of mucus during drug diffusion

Mucus is widely disseminated in the nasal cavity, oral cavity, respiratory tract, eyes, gastrointestinal tract, and reproductive tract to prevent the invasion of pathogenic bacteria and toxins. The mucus layer through its continuous secretion can prevent the passage of macromolecular substances such as pathogenic bacteria and toxins, thereby reducing the occurrence of inflammation. Without a doubt, mucus also hinders oral absorption. The physiological and biochemical properties of intestinal mucus and the different types of mucus barrier models need to be predominated. To find ways to increase the bioavailability of drugs in the future, this article summarizes mucus composition, barrier properties, mucus models, and mucoadhesive/mucopenetrating particles to highlight the information they can afford. Collectively, the review seeks to provide a state-of-the-art roadmap for researchers who must contend with this critical barrier to drug delivery.

"Mucus-on-Chip": A new tool to study the dynamic penetration of nanoparticulate drug carriers into mucus

The mucus covering of epithelial tissues presents one significant biological barrier to the uptake and absorption of particulate carriers. Improved understanding of the mechanisms mediating the transport of nanoparticles across such mucus layers would accelerate their development as optimised mucosal drug delivery formulations (e.g. via oral and rectal routes). Herein, an in vitro mucus model ("Mucus-on-Chip") was developed to enable the interaction and transport of functionalised nanoparticles and reconstituted mucus to be quantitatively investigated in real-time. We verified that the diffusion of nanoparticles into mucus is highly dependent on their biointerfacial properties. Muco-inert modification (PEGylation) significantly enhanced the mucopenetration of 50 nm and 200 nm nanoparticles, whereas limited mucopenetration was observed for pectin coated mucoadhesive nanoparticles. Furthermore, this model can be easily adapted to mimic specific physiological mucus environments. Mucus pre-treated with a mucolytic agent displayed reduced barrier function and therefore significantly accelerated mucopenetration of nanoparticles, which was independent of their size and biointerfacial properties. This new "Mucus-on-Chip" methodology provides detailed insight into the dynamics of nanoparticle-mucus interaction, which can be applied to refine the design of particulate formulations for more efficient mucosal drug delivery.

Molecular and cellular cues governing nanomaterial-mucosae interactions: from nanomedicine to nanotoxicology

Mucosal tissues constitute the largest interface between the body and the surrounding environment and they regulate the access of molecules, supramolecular structures, particulate matter, and pathogens into it. All mucosae are characterized by an outer mucus layer that protects the underlying cells from physicochemical, biological and mechanical insults, a mono-layered or stratified epithelium that forms tight junctions and controls the selective transport of solutes across it and associated lymphoid tissues that play a sentinel role. Mucus is a gel-like material comprised mainly of the glycoprotein mucin and water and it displays both hydrophilic and hydrophobic domains, a net negative charge, and high porosity and pore interconnectivity, providing an efficient barrier for the absorption of therapeutic agents. To prolong the residence time, absorption and bioavailability of a broad spectrum of active compounds upon mucosal administration, mucus-penetrating and mucoadhesive particles have been designed by tuning the chemical composition, the size, the density, and the surface properties. The benefits of utilizing nanomaterials that interact intimately with mucosae by different mechanisms in the nanomedicine field have been extensively reported. To ensure the safety of these nanosystems, their compatibility is evaluated in vitro and in vivo in preclinical and clinical trials. Conversely, there is a growing concern about the toxicity of nanomaterials dispersed in air and water effluents that unintentionally come into contact with the airways and the gastrointestinal tract. Thus, deep understanding of the key nanomaterial properties that govern the interplay with mucus and tissues is crucial for the rational design of more efficient drug delivery nanosystems (nanomedicine) and to anticipate the fate and side-effects of nanoparticulate matter upon acute or chronic exposure (nanotoxicology). This review initially overviews the complex structural features of mucosal tissues, including the structure of mucus, the epithelial barrier, the mucosal-associated lymphatic tissues and microbiota. Then, the most relevant investigations attempting to identify and validate the key particle features that govern nanomaterial-mucosa interactions and that are relevant in both nanomedicine and nanotoxicology are discussed in a holistic manner. Finally, the most popular experimental techniques and the incipient use of mathematical and computational models to characterize these interactions are described.

Visualization of the structure of native human pulmonary mucus

Human respiratory mucus lining the airway epithelium forms a challenging barrier to inhalation therapeutics. Therefore, structural elucidation of hydrated mucus is essential for an efficient drug delivery development. The structure of mucus has been primarily investigated by conventional electron microscopy techniques, which operate under vacuum conditions and require sample preparation steps that might alter the structure of mucus. In this study we investigated the impact of dehydration on mucus and analyzed the structure of mucus in its hydrated state. Cryo-scanning electron microscopy (Cryo-SEM) analysis of mucus showed, that during the process of sublimation, non-porous structure of mucus is transformed into a porous network. Similarly, images acquired by environmental scanning electron microscopy (ESEM), revealed a non-porous structure of hydrated mucus, while further observation at decreasing pressure demonstrated the strong influence of dehydration on mucus structure. We could successfully visualize the structural organization of the major gel forming mucin MUC5B in its hydrated state by employing stimulated emission depletion (STED) microscopy, which allowed resolving the nano-scale patterns of mucin macromolecules within the essentially pore-free mucus structure. The general structural organization of mucus components was addressed by confocal laser scanning microscopy (CLSM), which revealed the heterogeneous and composite structure of mucus. These results provide a novel view on the native structure of mucus and will affect drug delivery development.

Streptomycin sulphate loaded solid lipid nanoparticles show enhanced uptake in macrophage, lower MIC in Mycobacterium and improved oral bioavailability

Present study addresses the challenge of incorporating hydrophilic streptomycin sulphate (STRS; log P -6.4) with high dose (1 g/day) into a lipid matrix of SLNs. Cold high-pressure homogenization technique used for SLN preparation achieved 30% drug loading and 51.17 ± 0.95% entrapment efficiency. Polyethylene glycol 600 as a supporting-surfactant assigned small size (218.1 ± 15.46 nm) and mucus-penetrating property. It was conceived to administer STRS-SLNs orally rather than intramuscularly. STRS-SLNs remained stable on incubation for varying times in SGF or SIF. STRS-SLNs were extensively characterised for microscopic (TEM and AFM), thermal (DSC), diffraction (XRD) and spectroscopic (NMR and FTIR) properties and showed zero-order controlled release. Enhanced (60 times) intracellular uptake was observed in THP-1 and Pgp expressing LoVo and DLD-1 cell lines, using fluorescein-SLNs. Presence of SLNs in LoVo cells was also revealed by TEM studies. STRS-SLNs showed 3 times reduction in MIC against Mycobacterium tuberculosis H37RV (256182) in comparison to free STRS. It also showed better activity against both M. bovis BCG and Mycobacterium tuberculosis H37RV (272994) in comparison to free STRS. Cytotoxicity and acute toxicity studies (OECD 425 guidelines) confirmed in vitro and in vivo safety of STRS-SLNs. Single-dose oral pharmacokinetic studies in rat plasma using validated LCMS/MS technique or the microbioassay showed significant oral absorption and bioavailability (160% - 710% increase than free drug).

Intestinal Inflammation as a Dysbiosis of Energy Procurement: New Insights into an Old Topic

Inflammatory bowel disease (IBD) coincides with profound shifts in microbiota and host metabolic energy supply and demand. The gastrointestinal epithelium is anatomically positioned to provide a selective barrier between the anaerobic luminal microbiota and host lamina propria, with the microbiota and epithelium participating in an intricate energy exchange necessary for homeostasis. Maintenance and restoration of the barrier requires high energy flux and places significant demands on available substrates to generate ATP. It is recently appreciated that components of the microbiota contribute significantly to a multitude of biochemical pathways within and outside of the mucosa. Decades-old studies have appreciated that byproducts of the microbiota provide essential sources of energy to the intestinal epithelium, especially the colon. More recent work has unveiled the existence of numerous microbial-derived metabolites that support energy procurement within the mucosa. It is now appreciated that disease-associated shifts in the microbiota, termed dysbiosis, places significant demands on energy acquisition within the mucosa. Here, we review the topic of host- and microbial-derived components that influence tissue energetics in health and during disease.

MUC Glycoproteins: Potential Biomarkers and Molecular Targets for Cancer Therapy

MUC proteins have great significance as prognostic and diagnostic markers as well as a potential target for therapeutic interventions in most cancers of glandular epithelial origin. These are high molecular weight glycosylated proteins located in the epithelial lining of several tissues and ducts. Mucins belong to a heterogeneous group of large O-glycoproteins that can be either secreted or membrane-bound. Glycosylation, a post-translational modification affects the biophysical, functional and biochemical properties and provides structural complexity for these proteins. Aberrant expression and glycosylation of mucins contribute to tumour survival and proliferation in many cancers, which in turn activates numerous signalling pathways such as NF-kB, ERα, HIF, MAPK, p53, c-Src, Wnt and JAK-STAT, etc. This subsequently induces cancer cell growth, proliferation and metastasis. The present review mainly demonstrates the functional aspects of MUC glycoproteins along with its unique signalling mechanism and role of aberrant glycosylation in cancer progression and therapeutics. The importance of MUC proteins and its subtypes in a wide spectrum of cancers including but not limited to breast cancer, colorectal cancer, endometrial and cervical cancer, lung cancer, primary liver cancer, pancreatic cancer, prostate cancer and ovarian cancer has been exemplified with significance in targeting the same. Several patents associated with the MUC proteins in the field of cancer therapy are also emphasized in the current review.

The therapeutic potential of sialylated Fc domains of human IgG

Pathogens frequently use multivalent binding to sialic acid to infect cells or to modulate immunity through interactions with human sialic acid-binding immunoglobulin-type lectins (Siglecs). Molecules that interfere with these interactions could be of interest as diagnostics, anti-infectives or as immune modulators. This review describes the development of molecular scaffolds based on the crystallizable fragment (Fc) region of immunoglobulin (Ig) G that deliver high-avidity binding to innate immune receptors, including sialic acid-dependent receptors. The ways in which the sialylated Fc may be engineered as immune modulators that mimic the anti-inflammatory properties of intravenous polyclonal Ig or as blockers of sialic-acid-dependent infectivity by viruses are also discussed.

An overview of gastrointestinal mucus rheology under different pH conditions and introduction to pH-dependent rheological interactions with PLGA and chitosan nanoparticles

This review discusses the physicochemical and mechanical properties of porcine gastrointestinal mucus from a rheological point of view. Considering mucus as a viscoelastic gel that functions as a biological barrier by limiting particles passage, lubricating the gastrointestinal tract, and protecting the stomach from gastric acids. The viscoelastic and protective properties of mucus are mainly produced by its mucin network, which is stabilized through electrostatic, hydrophobic and hydrogen bonding interactions. Otherwise, mucus rheology is determined by its polyanionic nature at physiological pH. At neutral pH, mucus presents a viscous behavior produced by chains crosslinking. While, at acidic pH, mucus exhibits an elastic behavior related with the extended conformation that produces mucus gelation at the stomach. Additionally, rheology studies the degree of adhesion between a polymer-mucus mixture through rheological synergism, and how it varies at different pH conditions. Finally, mucoadhesion phenomenon is exemplified with chitosan (cationic) and poly (lactic-co-glycolic) acid (anionic) polymers.

Leveraging 3D Model Systems to Understand Viral Interactions with the Respiratory Mucosa

Respiratory viruses remain a significant cause of morbidity and mortality in the human population, underscoring the importance of ongoing basic research into virus-host interactions. However, many critical aspects of infection are difficult, if not impossible, to probe using standard cell lines, 2D culture formats, or even animal models. In vitro systems such as airway epithelial cultures at air-liquid interface, organoids, or 'on-chip' technologies allow interrogation in human cells and recapitulate emergent properties of the airway epithelium-the primary target for respiratory virus infection. While some of these models have been used for over thirty years, ongoing advancements in both culture techniques and analytical tools continue to provide new opportunities to investigate airway epithelial biology and viral infection phenotypes in both normal and diseased host backgrounds. Here we review these models and their application to studying respiratory viruses. Furthermore, given the ability of these systems to recapitulate the extracellular microenvironment, we evaluate their potential to serve as a platform for studies specifically addressing viral interactions at the mucosal surface and detail techniques that can be employed to expand our understanding.

Mucus barrier, mucins and gut microbiota: the expected slimy partners?

The gastrointestinal tract is often considered as a key organ involved in the digestion of food and providing nutrients to the body for proper maintenance. However, this system is composed of organs that are extremely complex. Among the different parts, the intestine is viewed as an incredible surface of contact with the environment and is colonised by hundreds of trillions of gut microbes. The role of the gut barrier has been studied for decades, but the exact mechanisms involved in the protection of the gut barrier are various and complementary. Among them, the integrity of the mucus barrier is one of the first lines of protection of the gastrointestinal tract. In the past, this 'slimy' partner was mostly considered a simple lubricant for facilitating the progression of the food bolus and the stools in the gut. Since then, different researchers have made important progress, and currently, the regulation of this mucus barrier is gaining increasing attention from the scientific community. Among the factors influencing the mucus barrier, the microbiome plays a major role in driving mucus changes. Additionally, our dietary habits (ie, high-fat diet, low-fibre/high-fibre diet, food additives, pre- probiotics) influence the mucus at different levels. Given that the mucus layer has been linked with the appearance of diseases, proper knowledge is highly warranted. Here, we debate different aspects of the mucus layer by focusing on its chemical composition, regulation of synthesis and degradation by the microbiota as well as some characteristics of the mucus layer in both physiological and pathological situations.

Observations of, and Insights into, Cystic Fibrosis Mucus Heterogeneity in the Pre-Modulator Era: Sputum Characteristics, DNA and Glycoprotein Content, and Solubilization Time

Airway obstruction with chronic inflammation and infection are major contributors to the lung damage and mortality of cystic fibrosis (CF). A better understanding of the congested milieu of CF airways will aid in improving therapeutic strategies. This article retrospectively reports our observations, and discusses insights gained in the handling and analysis of CF sputa. CF and non-CF mucus samples were surveyed for morphological features by electron microscopy and analyzed for the macromolecular dry weight (MDW), total protein, lipid, carbohydrate, and DNA. Mucus character was investigated with chemical solubilization time as a comparative tool. CF mucus appeared distinctly thick, viscous, and heterogeneous, with neutrophils as the dominant immune cell. CF sputum DNA content varied markedly for and between individuals (~1–10% MDW), as did solubilization times (~1–20 h). CF Sputum DNA up to 7.1% MDW correlated positively with solubilization time, whereas DNA >7.1% MDW correlated negatively. 3D analysis of CF sputa DNA, GP, and solubilization times revealed a dynamic and predictive relationship. Reflecting on the heterogeneous content and character of CF mucus, and the possible interplay in space and time in the respiratory tract of polymeric DNA and mucous glycoproteins, we highlight it’s potential to affect infection-related airway pathologies and the success of therapeutic interventions.

Streptococcus Thermophilus UASt-09 Upregulates Goblet Cell Activity in Colonic Epithelial Cells to a Greater Degree than other Probiotic Strains

Probiotics have been widely used in maintaining gastrointestinal health, despite their actual mechanism remaining obscure. There are several hypotheses behind the beneficial effects of probiotics including the regulation of intestinal barrier function and improvement in immune responses in the gastrointestinal system. Multiple probiotics have been introduced in the market as effective dietary supplements in improving gastrointestinal integrity, but there are no or few studies that demonstrate their underlying mechanism. In the current study, we investigated and compared the efficacy of four probiotics (based on different bacterial species) in refining gastrointestinal health by improving mucus biosynthesis and intestinal immune response under in-vitro conditions. By analyzing the gene expression of mucus biosynthesis and intestinal immune response markers, we found that probiotic Streptococcus thermophilus UASt-09 showed promising potential in refining mucosal barrier and gastrointestinal health in human colonic epithelial cells, as compared to other commercial probiotics.

Molecular Insights Into O-Linked Glycan Utilization by Gut Microbes

O-linked glycosylation is a post-translational modification found mainly in eukaryotic cells, which covalently attaches oligosaccharides to secreted proteins in certain threonine or serine residues. Most of O-glycans have N-acetylgalactosamine (GalNAc) as a common core. Several glycoproteins, such as mucins (MUCs), immunoglobulins, and caseins are examples of O-glycosylated structures. These glycans are further elongated with other monosaccharides and sulfate groups. Some of them could be found in dairy foods, while others are produced endogenously, in both cases interacting with the gut microbiota. Interestingly, certain gut microbes can access, release, and consume O-linked glycans as a carbon source. Among these, Akkermansia muciniphila, Bifidobacterium bifidum, and Bacteroides thetaiotaomicron are prominent O-linked glycan utilizers. Their consumption strategies include specialized α-fucosidases and α-sialidases, in addition to endo-α-N-acetylgalactosaminidases that release galacto-N-biose (GNB) from peptides backbones. O-linked glycan utilization by certain gut microbes represents an important niche that allows them to predominate and modulate host responses such as inflammation. Here, we focus on the distinct molecular mechanisms of consumption of O-linked GalNAc glycans by prominent gut microbes, especially from mucin and casein glycomacropeptide (GMP), highlighting the potential of these structures as emerging prebiotics.

Puerarin Rebuilding the Mucus Layer and Regulating Mucin-Utilizing Bacteria to Relieve Ulcerative Colitis

The colonic mucus barrier serves as a primary defense against enteric pathogens; destruction of this mucus layer has been observed in ulcerative colitis patients. This study aims to investigate the possibility of rebuilding the colon mucus layer through puerarin supplementation, which can stimulate mucin secretion and goblet cells differentiation. After puerarin supplementation, the thickness of colon mucus layer was increased and the permeability was reduced. The erosion of intestinal epithelium by bacteria was blocked, and the loss of epithelial integrity was alleviated. Puerarin also altered the composition of mucin-utilizing bacteria, which influenced the mucus permeability. Levels of short-chain fatty acids (SCFAs) were increased after puerarin supplementation, which as a direct source of energy for the proliferation of epithelia and goblet cells. This study demonstrated that enhancement of mucin secretion to relieve ulcerative colitis (UC) by puerarin supplementation is feasible, and the regulation of mucin-utilizing bacteria and the increased levels of SCFAs may be the main reasons.

Keeping It Together: Structures, Functions, and Applications of Viral Decoration Proteins

Decoration proteins are viral accessory gene products that adorn the surfaces of some phages and viral capsids, particularly tailed dsDNA phages. These proteins often play a "cementing" role, reinforcing capsids against accumulating internal pressure due to genome packaging, or environmental insults such as extremes of temperature or pH. Many decoration proteins serve alternative functions, including target cell recognition, participation in viral assembly, capsid size determination, or modulation of host gene expression. Examples that currently have structures characterized to high-resolution fall into five main folding motifs: β-tulip, β-tadpole, OB-fold, Ig-like, and a rare knotted α-helical fold. Most of these folding motifs have structure homologs in virus and target cell proteins, suggesting horizontal gene transfer was important in their evolution. Oligomerization states of decoration proteins range from monomers to trimers, with the latter most typical. Decoration proteins bind to a variety of loci on capsids that include icosahedral 2-, 3-, and 5-fold symmetry axes, as well as pseudo-symmetry sites. These binding sites often correspond to "weak points" on the capsid lattice. Because of their unique abilities to bind virus surfaces noncovalently, decoration proteins are increasingly exploited for technology, with uses including phage display, viral functionalization, vaccination, and improved nanoparticle design for imaging and drug delivery. These applications will undoubtedly benefit from further advances in our understanding of these versatile augmenters of viral functions.

Description of the unusual digestive tract of Platax orbicularis and the potential impact of Tenacibaculum maritimum infection

Background

Ephippidae fish are characterized by a discoid shape with a very small visceral cavity. Among them Platax orbicularis has a high economic potential due to its flesh quality and flesh to carcass ratio. Nonetheless, the development of its aquaculture is limited by high mortality rates, especially due to Tenacibaculum maritimum infection, occurring one to three weeks after the transfer of fishes from bio-secure land-based aquaculture system to the lagoon cages for growth. Among the lines of defense against this microbial infection, the gastrointestinal tract (GIT) is less studied. The knowledge about the morphofunctional anatomy of this organ in P. orbicularis is still scarce. Therefore, the aims of this study are to characterize the GIT in non-infected P. orbicularis juveniles to then investigate the impact of T. maritimum on this multifunctional organ.

Methods

In the first place, the morpho-anatomy of the GIT in non-infected individuals was characterized using various histological techniques. Then, infected individuals, experimentally challenged by T. maritimum were analysed and compared to the previously established GIT reference.

Results

The overlapped shape of the GIT of P. orbicularis is probably due to its constrained compaction in a narrow visceral cavity. Firstly, the GIT was divided into 10 sections, from the esophagus to the rectum. For each section, the structure of the walls was characterized, with a focus on mucus secretions and the presence of the Na⁺/K⁺ ATPase pump. An identification key allowing the characterization of the GIT sections using in toto histology is given. Secondly, individuals challenged with T. maritimum exhibited differences in mucus type and proportion and, modifications in the mucosal and muscle layers. These changes could induce an imbalance in the trade-off between the GIT functions which may be in favour of protection and immunity to the disadvantage of nutrition capacities.

Effect of dietary isoleucine on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris

The study investigated the effects of dietary isoleucine (Ile) on skin mucus barrier and epithelial physical barrier functions of hybrid bagrid catfish Pelteobagrus vachelli × Leiocassis longirostris. A total of 630 fish (33.11 ± 0.09 g) were fed semi-purified isonitrogenous diets containing 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile kg ^-1 diet for 8 weeks. The results indicated that dietary Ile increased (P < 0.05) in skin (1) mucus protein content and antimicrobial activity against three gram-negative bacteria (Aeromonas hydrophila, Escherichia coli, and Yersinia ruckeri) and two gram-positive bacteria (Streptococcus agalactiae and Staphylococcus aureus), (2) mucus lysofew information is available about the influencezyme (LZM), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, and complement 3 and 4 (C3 and C4) and immunoglobulin M (IgM) contents, (3) intelectin 1 (intl1), intelectin 2 (intl2), c-type-lysozyme (c-LZM), g-type-lysozyme (g-LZM), and β-defensin mRNA levels. Dietary Ile decreased (P < 0.05) reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl (PC) contents, and up-regulated (P < 0.05) CuZnSOD, GST, GPX1a, muc5ac, muc5b, zonula occludens-1 (ZO-1), zonula occludens-2 (ZO-2), occludin, and claudin 3 mRNA levels in skin. These results indicated that Ile improved skin mucus barrier function via increasing mucus protein, C3 and C4, and IgM contents and antibacterial factors activities, and promoted epithelial physical barrier function via decreasing skin antioxidant damage and improving tight junction structure in hybrid bagrid catfish.