Effects of the Escherichia coli Bacterial Toxin Cytotoxic Necrotizing Factor 1 on Different Human and Animal Cells: A Systematic Review

Cytotoxic necrotizing factor 1 (CNF1) is a bacterial virulence factor, the target of which is represented by Rho GTPases, small proteins involved in a huge number of crucial cellular processes. CNF1, due to its ability to modulate the activity of Rho GTPases, represents a widely used tool to unravel the role played by these regulatory proteins in different biological processes. In this review, we summarized the data available in the scientific literature concerning the observed in vitro effects induced by CNF1. An article search was performed on electronic bibliographic resources. Screenings were performed of titles, abstracts, and full-texts according to PRISMA guidelines, whereas eligibility criteria were defined for in vitro studies. We identified a total of 299 records by electronic article search and included 76 original peer-reviewed scientific articles reporting morphological or biochemical modifications induced in vitro by soluble CNF1, either recombinant or from pathogenic Escherichia coli extracts highly purified with chromatographic methods. Most of the described CNF1-induced effects on cultured cells are ascribable to the modulating activity of the toxin on Rho GTPases and the consequent effects on actin cytoskeleton organization. All in all, the present review could be a prospectus about the CNF1-induced effects on cultured cells reported so far.     

Construction of Chlorine Labeled ZnO–Chitosan Loaded Cellulose Nanofibrils Film with Quick Antibacterial Performance and Prominent UV Stability

In this study, novel “green” and highly stable biocidal materials composed of cellulose nanofibrils (CNF) and ZnO–chitosan (ZnO–CS) hybrids are constructed by combing vacuum filtration and heat‐press processing without the use of any organic solvent. CNF/ZnO–CS films are soaked in a 10% sodium hypochlorite aqueous solution to endow antibacterial activity. The chlorinated CNF/ZnO–CS samples and chlorinated CNF/ZnO‐CS (CNF/ZnO‐CS‐Cl) possess quick antimicrobial activity against Staphylococcus aureus and Escherichia coli within 30 min of contact compared with CNF and CNF/ZnO–CS controls. The addition of ZnO endows the films with remarkable UV light stability. After exposure to a UV chamber for 24 h, the chlorine loadings on the prepared samples decrease to 0.13%, where 76% of the chlorine loss can be regained after rechlorination. Furthermore, cytotoxicity evaluations reveal the feasibility of the films for in vitro applications. The prepared rechargeable CNF/ZnO–CS–Cl films will have many promising antibacterial applications.     

Effect of Carbon Nanofiber Functionalization on the Dispersion and Physical and Mechanical Properties of Polystyrene Nanocomposites

Summary: The effect of peroxide functionalization of carbon nanofibers (CNF) on the physical and mechanical properties of polystyrene (PS)–CNF nanocomposites prepared via melt mixing was studied. The CNF functionalization was evidenced by Raman spectroscopy, comparing the ratio of peaks at 1 371 and at 1 590 cm^?1 (peaks related to the disordered sp³‐hybridized carbon atom and to the graphitic structure of the sp²‐hybridized carbon atoms, respectively). The variation of the storage (E′) and tensile modulus (E) of the PS–CNF composites as a function of the untreated and peroxide treated CNF concentration were evaluated. Three different peroxide concentrations were used for treating the CNF. It was found that both E′ and E increase with CNF concentration and, in addition, increase further with the peroxide treated CNFs. Nonetheless, it was found that the greater the peroxide concentration used in treating the CNF, the greater the PS degradation via free radical attack on the polymer chain, with the corresponding negative effect on the storage and tensile modulus. Dispersion of the CNF was assessed using scanning and optical microscopy, and the positive effect of the peroxide treatment on the dispersion of the CNF is evidenced.

Tensile stress‐strain behavior of PS/CNF nanocomposites.     

Fabrication of elastic composite hydrogels using surface‐modified cellulose nanofiber as a multifunctional crosslinker

We fabricate composite hydrogels using surface‐modified cellulose nanofiber (CNF) and N‐isopropylacrylamide (NIPAm) as a multifunctional crosslinker and monomer, respectively. We expect to produce unique network structures that lead to elastomeric properties rarely reported for CNF‐based materials. The modification of CNF is performed to introduce polymerizable vinyl groups onto the surface of CNF via condensation between the surface hydroxyl groups and 3‐(trimethoxysilyl)propylmethacrylate. The modification and morphology of the surface‐modified CNF (mCNF) are confirmed by FTIR, solid‐state NMR, and FE‐SEM, respectively. We conduct in situ radical polymerization under various conditions using mixtures of the mCNF aqueous suspension, NIPAm monomer, radical initiator, and catalyst. The mechanical properties of the obtained hydrogels (water content = 90 wt %) are evaluated. The gels can be elastically stretched to more than 700 times their original lengths and exhibit an apparent shape recovery with a small permanent deformation (～1/5 of the applied deformation under the gravity field). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42906.     

Novel in situ carbon nanofiber/polydimethylsiloxane nanocomposites: Synthesis,morphology, and physico‐mechanical properties

A series of carbon nanofiber (CNF)/polydimethylsiloxane (PDMS)‐based nanocomposites was prepared by anionic ring opening polymerization of octamethylcyclotetrasiloxane (D₄) in presence of pristine CNF and amine‐modified CNF. A detailed study of morphology–property relationship of the nanocomposites was carried out in order to understand the effect of chemical modification and loading of filler on property enhancement of the nanocomposites. An elaborate comparison of structure and properties was carried out for the nanocomposites prepared by in situ and conventional ex situ methods. Pronounced improvement in degree of dispersion of the fillers in the matrix on amine modification of CNFs was reflected in mechanical properties of the modified nanocomposites. Maximum upliftment in mechanical properties was observed for in situ prepared amine modified CNF/hydroxyl PDMS nanocomposites. For 8 phr filler loading, tensile strength increased by 370%, while tensile modulus showed an increase of 515% compared with the virgin elastomer. Furthermore, in situ prepared unmodified CNF/hydroxyl PDMS nanocomposites showed an increase of 141°C in temperature of maximum degradation (T_max) for 8 phr CNF loading. These results were correlated with the morphological analysis through transmission electron microscopic studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A comparison of partially acetylated nanocellulose,nanocrystalline cellulose,and nanoclay as fillers for high‐performance polylactide nanocomposites

Partially acetylated cellulose nanofibers (CNF) were chemically extracted from sisal fibers and the performance of those CNF as nanofillers for polylactide (PLA) for food packaging applications was evaluated. Three PLA nanocomposites; PLA/CNF (cellulose nanofibers), PLA/CNC (nanocrystalline cellulose), and PLA/C30B (Cloisite^TM 30B, an organically modified montmorillonite clay) were prepared and their properties were evaluated. It was found that CNF reinforced composites showed a larger decrease on oxygen transmission rate (OTR) than the clay‐based composites; (PLA/CNF 1% nanocomposite showed a 63% of reduction at 23°C and 50% RH while PLA/C30B 1% showed a 26% decrease) and similar behavior on terms of water vapor barrier properties with 46 and 43%, respectively of decrease on water vapor transmission rate at 23°C and 50% RH (relative humidity). In terms of mechanical and thermomechanical properties, CNF‐based nanocomposites showed better performance than clay‐based composites without affecting significantly the optical transparency. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43257.     

Rac1/Wave2/Arp3 Pathway Mediates Rat Blood-Brain Barrier Dysfunction under Simulated Microgravity Based on Proteomics Strategy

The blood-brain barrier (BBB) is critical to maintaining central nervous system (CNS) homeostasis. However, the effects of microgravity (MG) on the BBB remain unclear. This study aimed to investigate the influence of simulated MG (SMG) on the BBB and explore its potential mechanism using a proteomic approach. Rats were tail-suspended to simulate MG for 21 days. SMG could disrupt the BBB, including increased oxidative stress levels, proinflammatory cytokine levels, and permeability, damaged BBB ultrastructure, and downregulated tight junctions (TJs) and adherens junctions (AJs) protein expression in the rat brain. A total of 554 differentially expressed proteins (DEPs) induced by SMG were determined based on the label-free quantitative proteomic strategy. The bioinformatics analysis suggested that DEPs were mainly enriched in regulating the cell–cell junction and cell–extracellular matrix biological pathways. The inhibited Ras-related C3 botulinum toxin substrate 1 (Rac1)/Wiskott–Aldrich syndrome protein family verprolin-homologous protein 2 (Wave2)/actin-related protein 3 (Arp3) pathway and the decreased ratio of filamentous actin (F-actin) to globular actin contributed to BBB dysfunction induced by SMG. In the human brain microvascular endothelial cell (HBMECs), SMG increased the oxidative stress levels and proinflammatory cytokine levels, promoted apoptosis, and arrested the cell cycle phase. Expression of TJs and AJs proteins were downregulated and the distribution of F-actin was altered in SMG-treated HBMECs. The key role of the Rac1/Wave2/Arp3 pathway in BBB dysfunction was confirmed in HBMECs with a specific Rac1 agonist. This study demonstrated that SMG induced BBB dysfunction and revealed that Rac1/Wave2/Arp3 could be a potential signaling pathway responsible for BBB disruption under SMG. These results might shed a novel light on maintaining astronaut CNS homeostasis during space travel.     

Efficacy of waterborne polyurethane to prevent the enzymatic attack on paper‐based materials

The chemical and biological deterioration of paper‐based materials is mainly due to the degradation of its main component, the cellulose. However, paper also contains small amounts of organic and inorganic additives which might influence its biodegradability. To protect the paper‐based materials against various degradative agents, coating treatments with polymeric materials might be developed. In this study, the protective effect of commercial waterborne polyurethanes (WPU) against an enzymatic attack was investigated. Uncoated and coated samples with WPU of newsprint were subjected to degradation by enzymatic complexes (cellulosomes) produced by Clostridium cellulolyticum for different incubation times and then characterized using several analytical techniques (energy dispersive X‐ray fluorescence, scanning electron microscopy, nuclear magnetic resonance, Raman and infrared spectroscopy) with the aim to assess if waterborne polyurethanes can be used in paper conservation, looking at their efficacy against the biodegradation induced by enzymes. The selected waterborne polyurethanes showed a high effectiveness in the protection of paper‐based materials when they were submitted to the enzymatic attack. Indeed, their presence delayed the destruction of the cellulose matrix and the release of both soluble sugars and paper additives. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,Chiral Separation,Absolute Configuration Assignment,and Biological Activity of Enantiomers of Retro‐1 as Potent Inhibitors of Shiga Toxin

The Shiga toxin (Stx) family is composed of related protein toxins produced by the bacteria Shigella dysenteriae and certain pathogenic strains of E. coli. No effective therapies for Stx intoxication have been developed yet. However, inhibitors that act on the intracellular trafficking of these toxins may provide new options for the development of therapeutic strategies. This study reports the synthesis, chromatographic separation, and pharmacological evaluation of the two enantiomers of Retro‐1, a compound active against Stx and other such protein toxins. Retro‐1 works by inhibiting retrograde transport of these toxins inside cells. In vitro experiments proved that the configuration of the stereocenter at position 5 is not crucial for the activity of this compound. X‐ray diffraction data revealed (S)‐Retro‐1 to be slightly more active than (R)‐Retro‐1.     

Effects of surface modification of carbon nanofibers on the mechanical properties of polyamide 1212 composites

In this study, the effects of carbon nanofiber (CNF) surface modification on mechanical properties of polyamide 1212 (PA1212)/CNFs composites were investigated. CNFs grafted with ethylenediamine (CNF‐g‐EDA), and CNFs grafted with polyethyleneimine (CNF‐g‐PEI) were prepared and characterized. The mechanical properties of the PA1212/CNFs composites were reinforced efficiently with addition of 0.3 wt % modified CNFs after drawing. The reinforcing effect of the drawn composites was investigated in terms of interfacial interaction, crystal orientation, crystallization properties and so on. After the surface modification of CNFs, the interfacial adhesion and dispersion of CNFs in PA1212 matrix were improved, especially for CNF‐g‐PEI. The improved interfacial adhesion and dispersion of CNFs in PA1212 matrix was beneficial to reinforcement of the composites. Compared with pure PA1212, improved degree of crystal orientation in the PA1212/CNF‐g‐PEI (CNF‐g‐EDA) composites was responsible for reinforcement of mechanical properties after drawing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41424.     

Biobased mineral‐oil barrier‐coated food‐packaging films

Toxic mineral oils can migrate into foods from cardboard boxes made of recycled fibers. This is an emerging issue for the whole dry‐food‐packaging industry. Breakfast cereals, for example, are typically packaged in boxes with or without inner bags and consumed without further processing. Currently, fossil‐based high‐density polyethylene (HDPE) films are used as a major raw material for such inner bags. However, HDPE is a very poor barrier against mineral‐oil migration. Biobased coatings from cellulose nanofibrils (CNFs), hydroxypropylated xylan, and hydroxypropylated cellulose were applied onto biobased high‐density polyethylene (bio‐HDPE) films, and the mineral‐oil barrier properties were evaluated. All of the coated films significantly decreased the migration of n‐decane, isobutylbenzene, 1‐cyclohexylbutane, 1‐cyclohexylheptane, and 1‐cyclohexyldecane. Biobased barrier bags prepared from (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxy oxidized CNF coated bio‐HDPE film protected the content to a great extent from mineral‐oil migration compared to noncoated bio‐HDPE and other commercial breakfast cereal‐bag films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44586.     

Synergistic effect of carbon nanofiber decorated with iron oxide in enhancing properties of styrene butadiene rubber nanocomposites

Elastomer nanocomposites reinforced with carbon nanofiber (CNF) decorated with metal nanoparticles exhibit excellent thermal, mechanical, and magnetic properties with low volume fraction of the reinforcement. Generally, metal nanoparticles are used to modify the surface of CNF, to improve their dispersion and contact resistance in the polymer matrix. In this study, Fe₂O₃ metal nanoparticles were decorated on CNF by electrostatic attraction via a green and facile solution‐based method. Interestingly, the CNF decorated with Fe₂O₃ (CNF‐Fe₂O₃)/elastomer improved both the tensile strength and the fatigue property of plain CNF/elastomer by as much as 57.2% and 27.2%, respectively. Moreover, the CNF‐Fe₂O₃/elastomer exhibited superior thermal conductivity, a twofold enhancement compared with carbon fibers. The elastomer nanocomposites consisting of CNF‐Fe₂O₃ also exhibited enhanced magnetic properties due to synergies between the Fe₂O₃ nanoparticles and the CNF. The elastomer nanocomposites prepared with CNF‐Fe₂O₃ will open significant new opportunities for preparing advanced elastomer nanocomposites for future engineering applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45376.     

Poly(ϵ‐caprolactone)‐functionalized carbon nanofibers by surface‐initiated ring‐opening polymerization

Carbon nanofibers (CNFs) were covalently functionalized with biodegradable poly(?‐caprolactone) (PCL) by in situ ring‐opening polymerization (ROP) of ?‐caprolactone in the presence of stannous octoate. Surface oxidation treatment of the pristine CNFs afforded carboxylic CNFs (CNF‐COOH). Reaction of CNF‐COOH with excess thionyl chloride (SOCl₂) and glycol produced hydroxyl‐functionalized CNFs (CNF‐OH). Using CNF‐OH as macroinitiator, PCL was covalently grafted from the surfaces of CNFs by ROP, in either the presence or absence of sacrificial initiator, butanol. The grafted PCL content was achieved as high as 64.2 wt %, and can be controlled to some extent by adjusting the feed ratio of monomer to CNF‐OH. The resulting products were characterized by FTIR, NMR, Raman spectroscopy, TGA, DSC, SEM, TEM, HRTEM, and XRD. Core–shell nanostructures were observed under HRTEM for the PCL‐functionalized CNFs because of the thorough grafting. The PCL‐grafted CNFs showed different melting and crystallization behaviors from the mechanical mixture of PCL and CNF‐OH. This approach to PCL‐functionalized CNFs opens an avenue for the synthesis, modification, and application of CNF‐based nanomaterials and biomaterials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Chemically modified cellulose nanofibril as an additive for two‐component polyurethane coatings

The increasing demand for the use of sustainable materials in industrial applications has created an urge to develop technologies that enable the use of biopolymers such as cellulose for the improvement of properties of commercial products. In this study, the potential of the silyl functionalized cellulose nanofibrils (CNF) as a reinforcing additive for the water‐ and solvent‐based two‐component polyurethane (PU) lacquer coatings was evaluated. The addition of the silylated CNF improved the abrasion resistance, strength, and elasticity of the PU coatings. When using the silylated CNF as an additive, the adhesion of the PU coatings was retained. The oxygen permeation rate of the silylated CNF films was strongly influenced by the nature of the solvent. The silylated CNF showed potential as a reinforcing additive even at low loadings in the two‐component PU lacquers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44801.     

Mushroom polysaccharides‐incorporated cellulose nanofiber films with improved mechanical,moisture barrier,and antioxidant properties

Mushroom polysaccharides (MP), including white MP, brown MP, and enoki MP, were incorporated into cellulose nanofiber (CNF). Studies on thermal property, structure, crystallinity, and morphology of CNF‐MP films revealed that MP was well interacted with and adsorbed onto CNF. Incorporation of MP significantly (P < 0.05) increased tensile strength and reduced water vapor permeability of CNF film. CNF‐MP films possessed higher antioxidant activity than CNF only or CNF‐chitosan film, and the antioxidant activity of released components from CNF‐MP films immersed in water was higher than that released from films immersed in methanol. Radical scavenging activity and reducing ability were major antioxidant mechanisms of CNF‐MP films. These trends were consistent with the results of total phenolics content released from films and the antioxidant activity of MP themselves. This study demonstrated CNF‐MP films may be used as packaging material for preventing oxidation and/or dehydration of food during storage. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46166.     

Thermal behavior of poly(ethylene‐co‐propylene) containing carbon nanofibers

The effect of carbon nanofiber on the thermal behavior of poly(ethylene‐co‐propylene) (PEP) as revealed by differential scanning calorimetry and thermogravimetric analysis is reported. Analysis showed faster crystallization of PEP at higher temperature upon cooling with the increase of carbon nanofiber (CNF) content. The crystallization behavior changed to a single narrow crystallization peak as compared with the broad double crystallization peak of the neat polymer. This demonstrates the nucleation ability of CNF to induce crystals with more uniform distribution. The modified‐Avrami approach was used to study the crystallization behavior. We found that the crystallization rate constant increased with addition of CNFs. The dimensionality of crystal growth was found not to depend significantly on the content of CNF. Thermal degradation in air was monitored using thermogravimetric analysis and observed that the incorporation of nanofiber greater than 2.4 vol% improves thermal stability of PEP. All these results indicate that CNFs can significantly help polymer processing and increase thermal stability of polymers. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

混合型TS-1/CNF催化剂的过滤性能及催化活性

纳米碳纤维（CNF）是一种新型的碳基催化剂载体。采用机械湿混的方式制得了混合型钛硅分子筛/纳米碳纤维（TS-1/CNF）催化剂,研究了其在水相体系中的过滤性能,以及在环己酮氨氧化反应中的催化活性。与单独TS-1相比,混合型TS-1/CNF催化剂的团聚体宏观尺寸较大,CNF交织形成的大量大孔非常有利于液体的穿透,使得TS-1/CNF催化剂具有良好的过滤性能,因而可改善TS-1在水相体系中的分离问题。SEM观察显示,CNF具有独特的长纤维结构以及较大的外表面,为TS-1微粒提供了较多的附着点,使得TS-1能均匀分布在CNF表面上。TS-1颗粒与直径处于相同尺度的CNF之间可能存在着较强的分子间作用力、静电作用力及疏水作用力,可避免分散和过滤过程中两者的分离。混合型TS-1/CNF催化剂上环己酮氨氧化反应的结果表明,环己酮的转化率接近100%,环己酮肟收率达98.4%,与纯TS-1的催化活性相当。     

Polyester composite water uptake and organic contaminant release affected by carbon nanofiber reinforcements

The incorporation of carbon nanofiber (CNF) into glass fiber (GF) composites is a potential route to extend polymer composite service‐life and enhance mechanical properties. Under nonstatic conditions, only limited information concerning water uptake and contaminant release properties of nanocomposite materials is currently available. Polyester composites containing GF and oxidized CNF were immersed in water for 30 days under nominal pressure at 23 °C, below the polymer's glass‐transition temperature. Water was analyzed and changed every three days to simulate water chemistry regeneration similar to exposures in flowing systems. Composites with oxidized CNF had greater water sorption capacity and leaching rates than CNF‐free composites. The total mass of organic contaminant released correlated with the amount of water sorbed by each composite (r² = 0.91), although CNF dispersion was found to vary greatly within composites. The greatest and least contaminant release rates were found for the polyester‐CNF and the polyester‐GF composites, respectively. While volatile aromatic resin solvents and stabilizer compounds were detected, their concentrations declined over the 30 day exposure period. We hypothesize that the hydrophilic nature of the oxidized CNF increased the water sorption capacity of the polyester composites. Additional studies are warranted that examine the impact of this phenomenon on composite mechanical and long‐term durability properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43724.     

Conformational Insights into the Control of CNF1 Toxin Activity by Peptidyl-Prolyl Isomerization: A Molecular Dynamics Perspective

The cytotoxic necrotizing factor 1 (CNF1) toxin from uropathogenic Escherichia coli constitutively activates Rho GTPases by catalyzing the deamidation of a critical glutamine residue located in the switch II (SWII). In crystallographic structures of the CNF1 catalytic domain (CNF1^CD), surface-exposed P768 and P968 peptidyl-prolyl imide bonds (X-Pro) adopt an unusual cis conformation. Here, we show that mutation of each proline residue into glycine abrogates CNF1^CD in vitro deamidase activity, while mutant forms of CNF1 remain functional on RhoA in cells. Using molecular dynamics simulations coupled to protein-peptide docking, we highlight the long-distance impact of peptidyl-prolyl cis-trans isomerization on the network of interactions between the loops bordering the entrance of the catalytic cleft. The energetically favorable isomerization of P768 compared with P968, induces an enlargement of loop L1 that fosters the invasion of CNF1^CD catalytic cleft by a peptide encompassing SWII of RhoA. The connection of the P968 cis isomer to the catalytic cysteine C866 via a ladder of stacking interactions is alleviated along the cis-trans isomerization. Finally, the cis-trans conversion of P768 favors a switch of the thiol side chain of C866 from a resting to an active orientation. The long-distance impact of peptidyl-prolyl cis-trans isomerizations is expected to have implications for target modification.