Selective Diffusion Barrier Research Articles

Interaction of mucin with viologen and acetate derivatives of calix[4]resorcinols

The mucus layer acts as a selective diffusion barrier that has an important effect on the efficiency of drug delivery systems in the human body. In this regard, currently the drug nanocarriers of various sizes and compositions are being widely developed to study their mucoadhesive properties i.e., the ability to interact with mucin. However, the effective interaction of drug composition with mucin does not guarantee the success due to the fact that there is a further barrier in the form of epithelial cells retained by calcium ions under the mucus layer. In this work, the interaction of mucin (porcine gastric mucin) with calixarenes is considered for the first time. The study of interaction between calixarenes, mucin and calcium ions by a complex of physicochemical methods showed that effective interaction with mucin requires cationic fragments, and binding with calcium is realized due to anionic fragments in the calixarene structure. Therefore, the combination of different chemical groups in the structure of drug nanocarrier plays an important role in successful mucosal drug delivery. Taking into account the wide possibilities of synthetic modification of the macrocyclic platform, calixarenes can find the application in the drug delivery across mucous barriers.

Disease-causing mutated ATLASTIN 3 is excluded from distal axons and reduces axonal autophagy

Mutations in the ER-network forming GTPase atlastin3 (ATL3) can cause axon degeneration of sensory neurons by not fully understood mechanisms. We here show that the hereditary sensory and autonomous neuropathy (HSAN)-causing ATL3 Y192C or P338R are excluded from distal axons by a barrier at the axon initial segment (AIS). This barrier is selective for mutated ATL3, but not wildtype ATL3 or unrelated ER-membrane proteins. Actin-depolymerization partially restores the transport of ATL3 Y192C into distal axons. The results point to the existence of a selective diffusion barrier in the ER membrane at the AIS, analogous to the AIS-based barriers for plasma membrane and cytosolic proteins. Functionally, the absence of ATL3 at the distal axon reduces axonal autophagy and the ER network deformation in the soma causes a reduction in axonal lysosomes. Both could contribute to axonal degeneration and eventually to HSAN.

Continuous mechanical tuning of plasmonic nanoassemblies for tunable and selective SERS platforms

The continuous tuning of plasmonic nanoassembly’s structure is the key to manipulate their optical and catalytic properties. Herein, we report a strategy of using macroscopic deformation to continuously tune the structure and optical activity of massive plasmonic nanoassemblies that are embedded in elastic polymer matrix. Plasmonic gold nanoparticles (Au NPs) are assembled to nanochains (Au NCs) with defined length and further embedded into polyvinylpyrrolidone (PVP) matrix. The nanostructure and plasmonic properties of massive Au NCs in this Au NCs-PVP film can be simultaneously and continuously tuned, simply by reversible mechanical deformation of this elastic film. In this way, the surface-enhanced Raman scattering (SERS) enhancement factor of this film as a SERS substrate can be mechanically modulated in the range of 100 to 6.8 × 107. Meanwhile, the PVP matrix also serves as a selective diffusion barrier to eliminate the fluorescence interference of large biomolecules, which enables the Au NCs-PVP film as a convenient SERS substrate for quick and direct analysis of small molecule analytes in biological samples and food, avoiding the complicate and time-consuming sample pretreatment process.

Microstructure and diffusion behavior in the multilayered oxides formed on a Co–W electroplated ferritic stainless steel followed by oxidation treatment

Numerous attempts have been made to improve the oxidation resistance and electrical conductivity of the interconnectors in solid oxide fuel cells. A Co–W alloy coating on ferritic stainless steel has attracted attention because the Co–W oxide layer formed by the oxidation treatment of the Co–W alloy coating has proven effective in reducing the outward diffusion of Cr and improving oxidation resistance. This study was designed to elucidate the diffusion behavior of elements and the barrier mechanism of the CoWO4 layer. After oxidation in air at 750°C, a dense, multilayered oxide formed, comprising (from the stainless steel substrate to the outer layer) Cr2O3, (Cr,Fe,Co)3O4, CoWO4, (Co,Fe)3O4, and Co3O4 layers. The CoWO4 layer and neighboring oxide layers were carefully analyzed by scanning electron microscopy and transmission electron microscopy with electron energy-loss spectroscopy, confirming the absence of trivalent cations (Co3+, Fe3+, and Cr3+) and the presence of Fe2+ ions in the CoWO4 layer; thus, CoWO4 functions as a selective diffusion barrier to trivalent cations, as hypothesized. The Cr-containing oxide layer grows based on the reaction between the metallic cations from the substrate and the inward-diffusing oxide ions, whereas Fe and Co can diffuse outward through CoWO4 as Fe2+ and Co2+ ions.

Microstructure, Formation, and Diffusion Kinetics of Multilayered Oxides Formed on a Co-W Electroplated Ferritic Stainless Steel Followed by Oxidation Treatment

Numerous attempts have been made to improve the oxidation resistance and electrical conductivity of the interconnectors in solid oxide fuel cells. A Co-W alloy coating on ferritic stainless steel has attracted attention because the Co-W oxide layer formed by the oxidation treatment of the Co-W alloy coating has proven effective in reducing the outward diffusion of Cr and improving oxidation resistance. This study was designed to elucidate the formation kinetics and diffusion barrier mechanism of the Co-W coating. After oxidation in air at 750 °C, a dense, multilayered oxide formed, comprising (from the stainless steel substrate to the outer layer) Cr oxide, Cr-Fe-Co oxide, Co-W oxide, Co-Fe oxide, and Co oxide layers. The CoWO4 layer and neighboring oxide layers were carefully analyzed by scanning electron microscopy and transmission electron microscopy, which revealed that the innermost Cr2O3 layer grows via the reaction between Cr in the substrate and inward-diffusing oxygen, whereas outward diffusion of Fe and Co is involved in the formation and growth of (Co,Fe)3O4 and Co3O4. Analysis by electron energy-loss spectroscopy confirmed the absence of trivalent cations (Co3+, Fe3+, and Cr3+) and the presence of Fe2+ ions in the CoWO4 layer; thus, CoWO4 functions as a selective diffusion barrier to trivalent cations as hypothesized.

Purely Polysaccharide-Based Biofilm Matrix Provides Size-Selective Diffusion Barriers for Nanoparticles and Bacteriophages.

Biofilms are complex mixtures of proteins, DNA, and polysaccharides surrounding bacterial communities as protective barriers that can be biochemically modified during the bacterial life cycle. However, their compositional heterogeneity impedes a precise analysis of the contributions of individual matrix components to the biofilm structural organization. To investigate the structural properties of glycan-based biofilms, we analyzed the diffusion dynamics of nanometer-sized objects in matrices of the megadalton-sized anionic polysaccharide, stewartan, the major biofilm component of the plant pathogen, Pantoea stewartii. Fluorescence correlation spectroscopy and single-particle tracking of nanobeads and bacteriophages indicated notable subdiffusive dynamics dependent on probe size and stewartan concentration, in contrast to free diffusion of small molecules. Stewartan enzymatic depolymerization by bacteriophage tailspike proteins rapidly restored unhindered diffusion. We, thus, hypothesize that the glycan polymer stewartan determines the major physicochemical properties of the biofilm, which acts as a selective diffusion barrier for nanometer-sized objects and can be controlled by enzymes.

Engineering bacterial microcompartments with heterologous enzyme cargos.

Bacterial microcompartments (BMCs) are intracellular proteinaceous organelles devoid of a lipid membrane that encapsulates enzymes of metabolic pathways. Salmonella enterica synthesizes propanediol-utilization BMCs containing enzymes involved in the degradation of 1,2-propanediol. BMCs can be designed to enclose heterologous proteins, paving the way to engineered catalytic microreactors. Here, we investigate broader applicability of this design principle by directing three different enzymes to the BMC. We demonstrate that β-galactosidase, esterase Est5, and cofactor-dependent glycerol dehydrogenase can be directed to the BMC and copurified with the microcompartment shell in a catalytically active form. We show that the BMC shell protects enzymes from pH-dependent but not from temperature stress. Moreover, we provide evidence that the heterologously expressed BMCs act as a moderately selective diffusion barrier for lipophilic small molecules.

Biomimetic Nanopores for Studying Yeast Nuclear Pore Transport

Nuclear pore complexes (NPC) acts as the gatekeeper to and from the nucleus in eukaryotic cells. NPCs function by creating a selective diffusion barrier for molecules bigger than 30kD (∼5 nm), where all proteins are barred from transport, except importer proteins that can freely pass. The mechanism underlying this intriguing selectivity of nuclear pore complexes is still under debate. A crucial element are the intrinsically disordered proteins with phenylalanine (F) and glycine (G) repeats, known as FG-NUPs, which form the centre of the NPC channel. Here, we fabricate and characterize biomimetic nanopores that mimic the NPC, with the aim to address the question of selective transport. We coat solid-state nanopores with key FG NUPs to create a biomimetic nanopores as a single-molecule detector. Yeast NSP1 (wild type or mutated) proteins were coated onto nanopore. The yeast importer protein KAP95 was found to be able to translocate across the biomimetic nanopores, unlike control protein tCherry which did not. We find the translocation times of KAP95 to be higher in FG-NUP-coated pores compared to uncoated nanopores. In mutated FG-NUP-NSP1 hydrophobic amino acid residues (F, I, L and V) were replaced with serine, thus making the NUPs hydrophilic. The translocation times of both KAP95 and tCherry through such pores are comparable with those for uncoated nanopores. We thus show that hydrophobic amino acid residues are essential for the cohesiveness and the selective behavior of FG-NUPs based nanopores. The lack of cohesiveness in mutated NSP1 coated nanopores is presumably caused by the lack of inter-repeat interactions. These findings explain why mutated-Nsp1-modified nanopores do not exhibit selectivity and contribute to the understanding of the mechanism of selectivity in the NPC at the simplest level.Key words: Nanopores, Biomimetics, Nuclear pore complex and FG NUPs.

Blood-brain barrier permeability imaging using perfusion computed tomography.

Background.The blood-brain barrier represents the selective diffusion barrier at the level of the cerebral microvascular endothelium. Other functions of blood-brain barrier include transport, signaling and osmoregulation. Endothelial cells interact with surrounding astrocytes, pericytes and neurons. These interactions are crucial to the development, structural integrity and function of the cerebral microvascular endothelium. Dysfunctional blood-brain barrier has been associated with pathologies such as acute stroke, tumors, inflammatory and neurodegenerative diseases.Conclusions.Blood-brain barrier permeability can be evaluated in vivo by perfusion computed tomography - an efficient diagnostic method that involves the sequential acquisition of tomographic images during the intravenous administration of iodinated contrast material. The major clinical applications of perfusion computed tomography are in acute stroke and in brain tumor imaging.

Influence of microemulsion-mucin interaction on the fate of microemulsions diffusing through pig gastric mucin solutions.

Mucus layer, a selective diffusion barrier, has an important effect on the fate of drug delivery systems in the gastrointestinal tract. To study the fate of microemulsions in the mucus layer, four microemulsion formulations with different particle sizes and lipid compositions were prepared. The microemulsion-mucin interaction was demonstrated by the fluorescence resonance energy transfer (FRET) method. Moreover, the microemulsions were observed aggregated into micron-sized emulsions by laser confocal microscopy. We concluded the microemulsion-mucin interaction not only led to microemulsions closely adhered to mucins but also destroyed the structure of microemulsions. At last, the diffusion of blank microemulsions and microemulsion-carried drugs (resveratrol and hymecromone) through mucin solutions was determined by the fluorescence recovery after photobleaching (FRAP) method and the Franz diffusion cell method. The results demonstrated the diffusion of microemulsions was significantly hindered by mucin solutions. The particle size of microemulsions had a negligible effect on the diffusion coefficients. However, the type of lipid played an important role, which could form hydrophobic interactions with mucins. Interestingly, microemulsion-carried drugs with different core/shell locations seemed to suffer different fates in the mucin solutions. The drug incorporated in the oil core of microemulsions, resveratrol, was transported through the mucus layer by the carriers, while the drug incorporated in the surfactant shell of microemulsions, hymecromone, was separated from the carriers and diffused toward the epithelium in the form of free molecules.

Slurry aluminizing mechanisms of Ni-based superalloys incorporating an electrosynthesized ceria diffusion barrier

This study investigates the effect of an electrosynthesized ceria interlayer on the growth mechanisms of a full TBC system sintered from a slurry containing spherical Al micro-particles. A potential Selective Diffusion Barrier (SDB) ability of the ceria interlayer appears. It is demonstrated that ceria allows the Al enrichment of the substrate while limiting the Cr upward diffusion and segregation of AlxCry. It is found that the ceria interlayer partially hinders the flow of solid and molten Al into the substrate at 700 °C from the spheres. Simultaneously, the flow of Al among the spheres results in the establishment of bridges and in the loss of sphericity all by maintaining a metallic core. In contrast, emptying of the particles and quick formation of δ-Ni2Al3 rapidly occur in the absence of ceria interlayer. Increasing the annealing temperature to 1100 °C for 2 h brings about the formation of a β-NiAl coating thicker than the one obtained without an interlayer and promotes thicker crusts and a greater sintering of the Al2O3 shell of the particles. This is proposed to result both from delayed Al inward diffusion and enhanced Ni outward diffusion promoted by the heat release accompanying the exothermic formation of the NixAly phases.

Effects of Interleukin-6 on the Expression of Tight Junction Proteins in Isolated Cerebral Microvessels from Yearling and Adult Sheep

Objectives: The blood-brain barrier is a selective diffusion barrier between brain parenchyma and the intravascular compartment. Tight junctions are integral components of the blood-brain barrier. Pro-inflammatory cytokines are important in the pathogenesis of brain injury and could modify the protein constituents of tight junctions. We hypothesized that interleukin-6 (IL-6) downregulates key protein constituents of endothelial tight junctions (e.g. occludin and claudin-5). Methods: We examined the effects of IL-6 on tight junction protein expression using an in vitro blood-brain barrier model. We isolated microvessels from yearling and adult ovine cerebral cortex and placed them into culture with IL-6 concentrations of 0 (control, phosphate-buffered saline), 1, 10, and 100 ng/ml for 24 h. Cerebral microvessels were harvested, Western immunoblot performed for occludin and claudin-5, densitometry performed, and results expressed as a ratio to control values. Results: Western immunoblot analysis showed that treatment with 100 ng/ml of IL-6, but not the lower concentrations, reduced (p < 0.05) occludin expression in microvessels from yearling and adult sheep and claudin-5 in microvessels from adult sheep. However, treatment with 10 ng/ml of IL-6 increased claudin-5 in microvessels from yearling sheep. The percent of lactate dehydrogenase released from the microvessels into the surrounding media was not increased by IL-6 treatment, suggesting that the reductions in tight junction proteins did not result from cell death. Treatment of adult cerebral cortical microvessels with IL-6 preincubated with anti-IL-6 monoclonal antibodies partially attenuated the reduction in claudin-5. Conclusion: We conclude that IL-6 modulates tight junction protein expression in cerebral cortical microvessels from yearling and adult sheep.

Blood–brain barrier

The blood –brain barrier (BBB) is a highly regulated interface that separates the peripheral circulation and central nervous system (CNS). It functions primarily as a selective diffusion barrier at the level of the cerebral microvascular endothelium. The BBB is often defined structurally as specialized endothelial cells lining the intraluminal portion of brain capillaries, but a more dynamic and functional definition recognizes the periendothelial accessory structures as integral components of the BBB. In addition to endothelial cells, the BBB is composed of the astrocytes, pericytes, neurons, and the extracellular matrix. This established neurovascular unit is essential for providing protection to the underlying brain cells and preserving the CNS homeostasis necessary for stable and coordinated neuronal activity. 1 In certain strategic positions, the BBB is functionally deficient. The unprotected regions include the pineal gland, neurohypophysis, area postrema, subfornical organ, median eminence, and the vascular organ of the lamina terminalis. These regions are collectively referred to as circumventricular organs and permit diffusion of blood-borne molecules, allowing regulation of endocrine and autonomic nervous system functions.

The porin and the permeating antibiotic: a selective diffusion barrier in Gram-negative bacteria

Gram-negative bacteria are responsible for a large proportion of antibiotic-resistant bacterial diseases. These bacteria have a complex cell envelope that comprises an outer membrane and an inner membrane that delimit the periplasm. The outer membrane contains various protein channels, called porins, which are involved in the influx of various compounds, including several classes of antibiotics. Bacterial adaptation to reduce influx through porins is an increasing problem worldwide that contributes, together with efflux systems, to the emergence and dissemination of antibiotic resistance. An exciting challenge is to decipher the genetic and molecular basis of membrane impermeability as a bacterial resistance mechanism. This Review outlines the bacterial response towards antibiotic stress on altered membrane permeability and discusses recent advances in molecular approaches that are improving our knowledge of the physico-chemical parameters that govern the translocation of antibiotics through porin channels.

Blood-neural Barrier: Intercellular Communication at Glio-Vascular Interface

The blood-neural barrier (BNB), including blood-brain barrier (BBB) and blood-retinal barrier (BRB), is an endothelial barrier constructed by an extensive network of endothelial cells, astrocytes and neurons to form functional "neurovascular units", which has an important role in maintaining a precisely regulated microenvironment for reliable neuronal activity. Although failure of the BNB may be a precipitating event or a consequence, the breakdown of BNB is closely related with the development and progression of CNS diseases. Therefore, BNB is most essential in the regulation of microenvironment of the CNS. The BNB is a selective diffusion barrier characterized by tight junctions between endothelial cells, lack of fenestrations, and specific BNB transporters. The BNB have been shown to be astrocyte dependent, for it is formed by the CNS capillary endothelial cells, surrounded by astrocytic end-foot processes. Given the anatomical associations with endothelial cells, it could be supposed that astrocytes play a role in the development, maintenance, and breakdown of the BNB. Therefore, astrocytes-endothelial cells interaction influences the BNB in both physiological and pathological conditions. If we better understand mutual interactions between astrocytes and endothelial cells, in the near future, we could provide a critical solution to the BNB problems and create new opportunities for future success of treating CNS diseases. Here, we focused astrocyte-endothelial cell interaction in the formation and function of the BNB.

The Tight Junction-specific Protein Occludin Is a Functional Target of the E3 Ubiquitin-protein Ligase Itch

Tight junctions create a highly selective diffusion barrier between epithelial and endothelial cells by preventing the free passage of molecules and ions across the paracellular pathway. Although the regulation of this barrier is still enigmatic, there is evidence that junctional transmembrane proteins are critically involved. Recent evidence confirms the notion that occludin, a four-pass integral plasma-membrane protein, is a functional component of the paracellular barrier. The overall hydrophilicity of occludin predicts two extracellular loops bounded by NH(2)- and COOH-terminal cytoplasmic domains. To date, the binding of the COOH terminus of occludin to intracellular proteins is well documented, but information concerning the function of the cytoplasmic NH(2) terminus is still lacking. Using yeast two-hybrid screening we have identified a novel interaction between occludin and the E3 ubiquitin-protein ligase Itch, a member of the HECT domain-containing ubiquitin-protein ligases. We have found that the NH(2)-terminal portion of occludin binds specifically to a multidomain of Itch, consisting of four WW motifs. This interaction has been confirmed by our results from in vivo and in vitro co-immunoprecipitation experiments. In addition, we provide evidence that Itch is specifically involved in the ubiquitination of occludin in vivo, and that the degradation of occludin is sensitive to proteasome inhibition.

Growth factor-induced morphological, physiological and molecular characteristics in cerebral endothelial cells

The capacity of vascular endothelial cells to modulate their phenotype in response to changes in environmental conditions is one of the most important characteristics of this cell type. Since different growth factors may play an important signalling role in this adaptive process we have investigated the effect of endothelial cell growth factor (ECGF) on morphological, physiological and molecular characteristics of cerebral endothelial cells (CECs). CECs grown in the presence of ECGF and its cofactor heparin exhibit an epithelial-like morphology (type I CECs). Upon removal of growth factors, CECs develop an elongated spindle-like shape (type II CECs) which is accompanied by the reorganization of actin filaments and the induction of alpha-actin expression. Since one of the most important functions of CECs is the creation of a selective diffusion barrier between the blood and the central nervous system (CNS), we have studied the expression of junction-related proteins in both cell types. We have found that removal of growth factors from endothelial cultures leads to the downregulation of cadherin and occludin protein levels. The loss of junctional proteins was accompanied by a significant increase in the migratory activity and an altered protease activity profile of the cells. TGF-beta1 suppressed endothelial migration in all experiments. Our data provide evidence to suggest that particular endothelial functions are largely controlled by the presence of growth factors. The differences in adhesiveness and migration may play a role in important physiological and pathological processes of endothelial cells such as vasculogenesis or tumor progression.

Three-dimensional analysis of vacuoles and surface invaginations of capillary endothelia in the eel rete mirabile

One layer of attenuated endothelia of continuous capillaries provides a partially selective diffusion barrier between the blood and the interstitium. Ultrastructures of membrane specialization without the known physiologic functions have been found in blood vessel endothelia. The vacuolar profiles or vacuole-like, membrane-bound structures, which are larger than plasmalemmal vesicles, have been observed routinely in normal endothelial cytoplasm or in blood vessels challenged by insults in electron microscopic studies. Three-dimensional information from serial sections is required to understand the organization and functions of vacuole-like structures in capillary endothelium. The capillaries in eel retia mirabile were perfused with electron-dense tracers, glutaraldehyde in buffer, and were processed for transmission electron microscopy. Ribbons of serial thin sections without counterstaining were examined under a transmission electron microscope. The vacuolar profiles inside endothelial cytoplasm were investigated with the techniques of serial section analysis and three-dimensional reconstruction from serial sections. The vacuole-like structures inside endothelial cytoplasm either were connected to extracellular (luminal, abluminal) compartments or existed as isolated vacuoles from serial section analysis. In the eight series examined in this study, six of ten vacuole-like structures were classified as isolated vacuoles inside endothelia, and their diameters ranged between 186 nm and 266 nm. Two of ten vacuole-like structures were found to extend to the luminal surface of capillaries as luminal, pocket-like invaginations. One of ten vacuole-like structures was found to be connected to the albuminal compartment, and another one existed as an extracellular compartment surrounded by endothelia. Three-dimensional projection of the vacuolar compartments from serial sections showed that endothelial cytoplasm of sheet shape protruded and folded over adjacent endothelium. Three-dimensional information from serial sections reveals the organization of vacuolar profiles and pocket-like invaginations from the cell surfaces in capillary endothelium. The vacuolar profiles in capillary endothelia in two-dimensional electron photomicrographs may represent the extracellular compartments surrounded by the endothelial finger-like extensions. The results indicate that the luminal and abluminal surfaces of the capillary lumen are not smooth or static, and endothelia may change their shape in three dimensions through cytoplasmic protrusions when the tissue environment changes.

The influence of cobalt on the oxysulfidation of brass

The effect of Co on the oxysulfidation behaviour of vulcanized brass sheets has been studied by means of auger depth profiling combined with the statistical technique Maximum Likelihood Common Factor Analysis (MLCFA). The chemical information, inherently present in the strongly overlapping auger spectra, could be extracted by MLCFA and, hence, allowed a detailed chemical characterization of the oxysulfidation layer at the rubber brass interface. From this study it follows that Co acts as a selective diffusion barrier, promoting the growth of CuxS at the rubber interface, while retarding the ZnS production. Some aspects of this behaviour can lead to a better understanding of the oxysulfidation mechanism in the presence of ternary elements.

Properties of PECVD SiOx N y Films as Selective Diffusion Barrier

Properties of silicon oxynitride films on substrates formed by plasma‐enhanced chemical vapor deposition (PECVD) employed as diffusion barriers have been reported. The relation between the refractive index and the composition of films, the thermal stability and the barrier ability to Zn impurity diffusion have been discussed; and we propose an optimum range of the refractive index of the PECVD films for excellent diffusion barriers and a suitable structure for selective diffusion barriers.