Carboxyethylester-polyrotaxanes as a new calcium chelating polymer: synthesis, calcium binding and mechanism of trypsin inhibition

Synthesis of cyclodextrin-based polyrotaxanes and polycatenanes for supramolecular pharmaceutical sciences

Cyclodextrins (CDs) are essential in the pharmaceutical industry and have long been used as food and pharmaceutical additives. CD-based interlocked molecules, such as rotaxanes, polyrotaxanes, catenanes, and polycatenanes, have been synthesized and have attracted considerable attention in supramolecular chemistry. Among them, CD polyrotaxanes have been employed as slide-ring materials and biomaterials. CD polycatenanes are new materials; therefore, to date, no examples of applied research on CD polycatenanes have been reported. Consequently, we expect that applied research on CD polycatenanes will accelerate in the future. This review article summarizes the syntheses and structural analyses of CD polyrotaxanes and polycatenanes to facilitate their applications in the pharmaceutical industry. We believe that this review will promote further research on CD-based interlocked molecules.

Calcium phosphate-adsorbable and acid-degradable carboxylated polyrotaxane consisting of β-cyclodextrins suppresses osteoclast resorptive activity

Recently, the potential of β-cyclodextrin-thread acid-degradable polyrotaxane (AdPRX) has been emphasized as a therapeutic agent for cholesterol-related metabolic disorders. In this study, we investigated whether carboxymethyl carbamate-modified AdPRX (CMC-AdPRX) can be used for adsorption to calcium phosphate to treat bone diseases. We first synthesized CMC-AdPRX and used it to coat the calcium phosphate plate. RAW264.7 cells were then differentiated into osteoclasts via a receptor activator of nuclear factor-κB ligand, and the number of osteoclasts and the area of absorption lacunae were determined. The number of tartrate-resistant acid phosphatase-positive multinucleated cells was reduced on the CMC-AdPRX-coated plate. The area of the absorption lacunae was smaller with CMC-AdPRX than with AdPRX, which was not carboxy-modified. Our results suggest that CMC-AdPRX can adsorb to calcium phosphate and act on differentiated osteoclasts to suppress their functional expression.

Weakly acidic carboxy group-grafted β-cyclodextrin-threaded acid-degradable polyrotaxanes for modulating protein interaction and cellular internalization

To improve the therapeutic potential of β-cyclodextrin (β-CD)-threaded acid-degradable polyrotaxanes (β-CD PRXs) in cholesterol-related metabolic disorders, we investigated the effect of carboxylation of β-CD PRXs on intracellular uptake. In this study, we established a synthetic method for the modification of carboxylalkyl carbamates on β-CD PRXs without degradation and synthesized three series of carboxyalkyl carbamate group-modified β-CD PRXs with different alkyl spacer lengths. The modification of carboxymethyl carbamate (CMC), carboxyethyl carbamate (CEC), and carboxypropyl carbamate (CPC) on the β-CD PRXs slightly reduced the interaction of the PRXs with the lipid layer model compared with the modification of 2-(2-hydroxyethoxy)ethyl carbamate (HEE-PRX), which was used in our previous studies. However, all the carboxylated β-CD PRXs showed a significantly stronger interaction with a protein model compared with HEE-PRX. The carboxylated β-CD PRXs showed significantly high intracellular uptake, through macrophage scavenger receptor A (MSR-A)-mediated endocytosis, in MSR-A-positive RAW 264.7 cells compared with HEE-PRX. Interestingly, the carboxylated β-CD PRXs also showed significantly higher intracellular uptake even in MSR-A-negative cells compared with HEE-PRX. Carboxylated β-CD PRXs are considered to strongly interact with other membrane proteins, resulting in high intracellular uptake. The length of the alkyl spacer affected the intracellular uptake levels of carboxylated PRXs, however, this relationship was varied for different cell types. Furthermore, none of the carboxylated β-CD PRXs exhibited cytotoxicity in the RAW 264.7 and NIH/3T3 cells. Altogether, carboxylation of β-CD PRXs is a promising chemical modification approach for their therapeutic application because carboxylated β-CD PRXs exhibit high cellular internalization efficiency in MSR-A-negative cells and negligible toxicity.

Post-synthesis modification of slide-ring gels for thermal and mechanical reconfiguration

Ring-sliding behavior in polyrotaxanes imbues gels, elastomers, and glasses with remarkable stress-dissipation and actuation properties. Since these properties can be modulated and tuned by structural parameters, many efforts have been devoted to developing synthetic protocols that define the structures and properties of slide-ring materials. We introduce post-synthetic modifications of slide-ring gels derived from unmodified α-cyclodextrin and poly(ethylene glycol) polyrotaxanes that enable (i) actuation and control of the thermo-responsive lower critical solution temperature (LCST) behavior of ring-modified slide-ring hydrogels, and (ii) chemically bonding separate gels into hybrid or shape-reconfigured macro-structures with a slide-ring adhesive solution. The mechanical properties of the post-modified gels have been characterized by shear rheology and uniaxial tensile tests, while the corresponding xerogels were characterized by wide-angle X-ray scattering. These demonstrations show that post-synthetic modification offers a practical solution for re-configuring the properties and shapes of slide-ring gels.

Applications of liquid crystals in biosensing

Liquid crystals (LCs), as a promising branch of highly-sensitive, quick-response, and low-cost materials, are widely applied to the detection of weak external stimuli and have attracted significant attention. Over the past decade, many research groups have been devoted to developing LC-based biosensors due to their self-assembly potential and functional diversity. In this paper, recent investigations on the design and application of LC-based biosensors are reviewed, based on the phenomenon that the orientation of LCs can be directly influenced by the interactions between biomolecules and LC molecules. The sensing principle of LC-based biosensors, as well as their signal detection by probing interfacial interactions, is described to convert, amplify, and quantify the information from targets into optical and electrical parameters. Furthermore, commonly-used LC biosensing targets are introduced, including glucose, proteins, enzymes, nucleic acids, cells, microorganisms, ions, and other micromolecules that are critical to human health. Due to their self-assembly potential, chemical diversity, and high sensitivity, it has been reported that tunable stimuli-responsive LC biosensors show bright perspectives and high superiorities in biological applications. Finally, challenges and future prospects are discussed for the fabrication and application of LC biosensors to both enhance their performance and to realize their promise in the biosensing industry.

Stimuli-Responsive Microarray Films for Real-Time Sensing of Surrounding Media, Temperature, and Solution Properties via Diffraction Patterns

Stimuli-responsive polymers have attracted increasing attention over the years due to their ability to alter physiochemical properties upon external stimuli. However, many stimuli-responsive polymer-based sensors require specialized and expensive equipment, which limits their applications. Here an inexpensive and portable sensing platform of novel microarray films made of stimuli-responsive polymers is introduced for the real-time sensing of various environmental changes. When illuminated by laser light, microarray films generate diffraction patterns that can reflect and magnify variations of the periodical microstructure induced by surrounding invisible parameters in real time. Stimuli-responsive polyelectrolyte complexes are structured into micropillar arrays to monitor the pH variation and the presence of calcium ions based on reversible swelling/shrinking behaviors of the polymers. A pH hysteretic effect of the selected polyelectrolyte pair is determined and explained. Furthermore, polycaprolactone microchamber arrays are fabricated and display a thermal-driven structural change, which is exploited for photonic threshold temperature detection. Experimentally observed diffraction patterns are additionally compared with rigorous coupled-wave analysis simulations that prove that induced diffraction pattern alterations are solely caused by geometrical microstructure changes. Microarray-based diffraction patterns are a novel sensing platform with versatile sensing capabilities that will likely pave the way for the use of microarray structures as photonic sensors.

Porphyrin-terminated nanoscale fluorescent polyrotaxane as a biodegradable drug carrier for anticancer research

Drug delivery carriers hold tremendous promise for improving cancer treatment, and polyrotaxane (PR) has shown excellent drug-carrying properties. However, there have been some reports that, when used as a drug carrier, water-soluble PR is not easily labeled with organic fluorescent dyes. Herein, we synthesized a drug-loaded fluorescent porphyrin-terminated PR (PR-COOH) which can be used as a tracer material in drug and gene delivery. The structure, morphology and zeta potential of PR-COOH were characterized by nuclear magnetic resonance, high-resolution transmission electron microscopy and zeta potentiometry. In this research, cisplatin (CDDP) is used as a model drug. The zeta potential, drug encapsulation efficiency and drug release of CDDP-loaded PR (PR-COOH-Pt) were studied. Confocal laser scanning microscopy showed that PR-COOH could be internalized by HeLa and CT26 cells. The antitumor efficacy of PR-COOH-Pt was investigated in vitro by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and in vivo by a xenograft tumor model. The results showed that PR-COOH-Pt could significantly inhibit tumor growth; thus PR-COOH-Pt has a promising role in cancer therapy.

Scavenger Receptor A-Mediated Targeting of Carboxylated Polyrotaxanes to Macrophages and the Impacts of Supramolecular Structure

Because macrophages are involved in the pathology of many diseases, targeting delivery of therapeutic molecules to macrophages is important issue. Polyrotaxanes (PRXs) composed of multiple cyclodextrins threaded with a linear polymer were utilized as a therapeutic agent for metabolic disease and for regulating cellular metabolism. For targeting delivery of PRXs to macrophages, carboxyethyl ether group-modified PRXs (CEE-PRXs) are designed for promoting interaction to macrophage scavenger receptor class A (SR-A). The cellular internalization of anionic CEE-PRXs in SR-A-positive macrophage-like cells (RAW264.7) is remarkably higher than that of nonionic PRX, whereas the cellular internalization efficiency in SR-A-negative cells is comparable between anionic and nonionic PRX. Furthermore, the molecular weight of axle polymer and the number of CEE groups modified on PRX are found to be the predominant factors governing cellular internalization efficiency in SR-A-positive RAW264.7 cells. Thus, CEE-PRXs are a promising design for targeting delivery of PRXs to macrophages.

A two-stage cold isostatic pressing and gelling approach for fabricating a therapeutically loaded amorphous calcium polyphosphate local delivery system

Local delivery systems have taken on a greater clinical focus for osteomyelitis therapy owing to their ability to overcome many disadvantages of systemic delivery. This study reports for the first time the capacity to fabricate strontium- and vancomycin-doped calcium polyphosphate beads using a two-stage cold isostatic pressing and gelling approach. The fabricated beads were of uniform shape and diameter, and upon gelling exhibited reduced porosity. Of greatest significance in the subsequent in vitro study was the improvement of bead long-term structural stability upon vancomycin incorporation; a characteristic that further encourages the extended release of therapeutically relevant levels of antibiotic. Overall, this study provides support for the inclusion of a cold isostatic pressing step in the fabrication of a therapeutically loaded calcium polyphosphate bead-based local delivery system intended for osteomyelitis treatment.

Nanoparticles assembled via pH-responsive reversible segregation of cyclodextrins in polyrotaxanes

Supramolecular polymers with monomers bound together by secondary interactions, such as polyrotaxanes (PRXs), consisting of alpha cyclodextrin (αCD) threaded onto poly(ethylene glycol) (PEG), have attracted interest as a result of their ability to overcome physical limitations present in conventional, covalently structured polymers. Herein, we describe the formation of pH-responsive supramolecular assemblies from carboxyethylester bearing αCD and PEG PRXs. These PRXs were formed using PEG of Mw 20 kDa and a threading degree of 28%. Upon charge neutralisation the threaded αCDs co-localise, resulting in aggregation of the PRXs and the formation of a suspension by self-assembly. This process is shown to be reversible and possible via the mobility of CDs along the PEG guest chain. As a result of the inherent properties of PRXs, such as enhanced multivalent interactions and degradation, these responsive supramolecular polymers are expected to be of interest in fields where PRX-based materials have already found application, including paints, self-healing materials, surface coatings, and polymer therapeutics.

Supramolecular polymers based on cyclodextrins for drug and gene delivery

Supramolecular polymers based on cyclodextrins (CDs) have inspired interesting and rapid developments as novel biomaterials in a broad range of drug and gene delivery applications, due to their low cytotoxicity, controllable size, and unique architecture. This review will summarize the potential applications of polyrotaxanes in the field of drug delivery and gene delivery. Generally, cyclodextrin-based biodegradable polypseudorotaxane hydrogels could be used as a promising injectable drug delivery system for sustained and controlled drug release. Temperature-responsive, pH-sensitive, and controllable hydrolyzable polyrotaxane hydrogels have attracted much attention because of their controllable properties, and the self-assembly micelles formed by amphiphilic copolymer threaded with CDs could be used as a carrier for controlled and sustained drug release. Polyrotaxanes with drug or ligand conjugated CDs threaded on a polymer chain with a biodegradable end group could be useful for controlled and multivalent targeted delivery. In the field of gene delivery, cationic polyrotaxanes consisting of multiple OEI-grafted CDs threaded on a block copolymer chain are attractive non-viral gene carries due to the strong DNA-binding ability, low cytotoxicity, and high gene delivery capability. Furthermore, cytocleavable end-caps were introduced in the polyrotaxane systems in order to ensure efficient endosomal escape for intracellular trafficking of DNA. The development of the supramolecular approach using CD-containing polyrotaxanes is expected to provide a new paradigm for biomaterials.

Polyrotaxanes composed of β-cyclodextrin and polydimethylsiloxanes: synthesis, morphology and thermal behavior

Epoxy-terminated polydimethylsiloxanes (E-PDMSs) of different molecular weight Mn were proved to undergo inclusion complexation into the inner cavity of β-cyclodextrin (β-CD), resulting in polyrotaxanes (PRots). The dethreading of the macrocycle was prevented by blocking the siloxane chain with a bulky substituent derived from 4-aminophenyltriphenyl methane (APhTPhM). As revealed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), wide-angle X-ray diffraction and statistical analysis of SEM images, the thermal properties and the morphology of polyrotoxanes are dependent upon Mn, β-CD/E-PDMS molar ratio and the presence of free β-CD in the complexes.

Recent advances in the preparation of cyclodextrin-based polyrotaxanes and their applications to soft materials

The present review article deals with recent novel studies on the preparation and application of polyrotaxanes comprised of cyclodextrins (CDs) and various linear polymers, especially poly(ethylene glycol) (PEG). First, a brief introduction of the historical background of the pioneering work on the preparation of an inclusion complex and polyrotaxane is provided. Subsequently, the authors have focused on the recently developed solvent systems for the polyrotaxane. These new solvents are interesting from two fundamental viewpoints: (1) from the perspective of the clarification of the hydrogen-bonding-based dissolution mechanism of polyrotaxanes; and (2) from the practical viewpoint of the preparation of modified polyrotaxanes or slide-ring gels containing ionic liquids. A wide variety of polyrotaxane derivatives, whose cyclodextrin moiety was modified to carry various functional groups, and their intriguing characteristics are introduced in this article. Finally, many instances of the application of the PEG-CD polyrotaxane to soft materials, such as gels, molecular tubes and multivalent ligand systems, are summarized.

Protective effect of Carbopol on enzymatic degradation of a peptide-like substrate. I: Effect of various concentrations and grades of Carbopol and other reaction variables on trypsin activity

The purpose of this study was to determine and compare the effect of various concentrations and grades of Carbopol on trypsin-induced degradation of a prototype substrate, N(alpha)-benzoyl-L-arginine ethyl ester hydrochloride (BAEE). Effect of other reaction variables, such as viscosity and ionic strength of the medium on the trypsin activity, was also analyzed simultaneously. Four concentrations and three commercially available grades of Carbopol were used. The effect of Carbopol was expressed in terms of change in the velocity of degradation reaction. A modified trypsin assay was developed and used for analysis. Up to a concentration of 0.35% w/v, Carbopol 934P showed a concentration-dependent increase in its ability to reduce the rate of enzymatic hydrolysis of BAEE. Similar inhibitory effect was observed with all three grades of Carbopol. The activity of trypsin was unaffected by other reaction variables, suggesting that interaction between the protein and the polymer could be the mechanism responsible for reduced trypsin activity. This study suggests that Carbopol can be a useful excipient for oral delivery of bioactive proteins and peptides, due to its ability to reduce the enzyme-induced degradation of these agents.

Effects of conditions for preparing nanoparticles composed of aminoethylcarbamoyl-β-cyclodextrin and ethylene glycol diglycidyl ether on trap efficiency of a guest molecule

Nanoparticles comprising copolymers of aminoethylcarbamoyl-beta-cyclodextrin (AEC-beta-CD) and ethylene glycol diglycidyl ether (EGDGE) are prepared by an interfacial polyaddition reaction in a miniemulsion system. Polymers are formed in a W/O emulsion containing 0.25-10.0% (w/w) water and 5.0% (w/w) surfactant (MO-3S, tetraglycerin monoester, HLB 8.8), where simple particles are predominantly obtained when the water content is 1.0% and 5.0%. Notably, nano-size small particles (diameter: 0.3 microm) are formed under the condition of 5.0% water and 5.0% surfactant, which have the highest beta-CD contents (75.5 wt.%) and the most positive zeta-potential (53.6 mV). The zeta-potential measurement indicates that the obtained particles have positive charge due to protonation of their amino groups below around pH 10. Actually, uptake of 8-anilino-1-naphthalenesulfonic acid (ANS) bearing negative charge (SO(3)(-)) and moderate hydrophobicity depends on the magnitude of zeta-potential of the particles; viz., the particles with zeta-potential of 53.6 mV show the highest efficiency of uptake. The diameter and the beta-CD contents are closely related with the water/surfactant ratio, and the zeta-potentials are dependent on both the diameter and the beta-CD contents. Inclusion of ANS into the CD cavity of EGDGE/AEC-beta-CD particles can be controlled by electrostatic interaction between ANS (negatively charged) and the particle (positively charged). Namely, synergistic effect of cavity-inclusion and electrostatic interaction can dominate the uptake of guest molecules by the particles.

Preparation ofα-Cyclodextrin-Terminated Polyrotaxane Consisting ofβ-Cyclodextrins and Pluronic as a Building Block of a Biodegradable Network

A beta-CD-based biodegradable polyrotaxane was prepared by capping both terminals of polypseudorotaxane consisting of hydrazide-terminated PEG-block-PPG-block-PEG (Pluronic P-105) and beta-CD-succinates with mono-aldehyde alpha-CDs. By decreasing pH, the fluorescent intensity of TNS was increased with time, indicating cleavage of the terminal hydrazone bonds followed by beta-CD-succinate release. The terminal alpha-CD moieties of the polyrotaxane are useful for self-assembled formation with some guest molecules. [Diagram: see text]

Incorporation of different antibiotics into carbonated hydroxyapatite coatings on titanium implants, release and antibiotic efficacy

Carbonated hydroxyapatite (CHA) coatings were applied onto titanium implants by using a biomimetic precipitation method. Different antibiotics were incorporated into the CHA coatings and their release and efficacy against bacteria growth were studied in vitro. The following antibiotics were used within this study: cephalothin, carbenicillin, amoxicillin, cefamandol, tobramycin, gentamicin and vancomycin. Increased concentrations of antibiotics in the coating solution led to a higher quantity of antibiotic incorporated into the CHA coating. Some antibiotics were better incorporated than others depending on their chemical structure. Antibiotics, containing carboxylic groups such as cephalothin, carbenicillin and cefamandol, were better incorporated than antibiotics lacking these groups. A bacterial inhibition test on Staphylococcus aureus bacteria showed inhibition of growth for all antibiotics that were released from the CHA coating. A release test was conducted in phosphate buffer saline PBS at pH 7.4 and 37 degrees C and showed that antibiotics containing carboxylic groups like cephalothin were slower released from the CHA coating than others. These results suggest that certain antibiotics are able to bind/chelate with calcium, resulting in a better incorporation into the CHA coating and a slower release. Antibiotics incorporated in CHA coatings on titanium implants might be used to prevent post-surgical infections and to promote bone-bonding of orthopedic devices.

Controlling the mechanism of trypsin inhibition by the numbers of α-cyclodextrins and carboxyl groups in carboxyethylester-polyrotaxanes

Carboxyethylester-polyrotaxanes (CEE-polyrotaxanes) with the various number of CEE-modified alpha-cyclodextrins (CEE-alpha-CDs) were synthesized, and the effects of the number of CEE-alpha-CDs on calcium binding and trypsin inhibition were investigated. Calcium binding affinity was dependent on the density of the CEE groups accompanied with the number of alpha-CD threading in the CEE-polyrotaxanes. The high number of CEE-alpha-CDs leads to greater inhibition of trypsin activity than poly(acrylic acid), which is mainly due to the good calcium binding affinity. The CEE-polyrotaxane with the smallest number of CEE-alpha-CDs temporally interacted with trypsin, which was well correlated with the inhibition and recovery of trypsin activity. Therefore, the number of CEE-alpha-CDs in the CEE-polyrotaxanes can control the inhibition mechanism of trypsin activity.

Supramolecular Design for Multivalent Interaction: Maltose Mobility along Polyrotaxane Enhanced Binding with Concanavalin A

High molecular mobility of maltose-conjugated alpha-cyclodextrins (alpha-CDs) along a poly(ethylene glycol) (PEG) chain due to the mechanically locked structure of polyrotaxanes enhanced multivalent interactions between maltose and concanavalin A (Con A). When maltose groups are conjugated with alpha-CDs that were threaded onto a PEG capped with benzyloxycarbonyl l-tyrosine (polyrotaxane), Con A-induced hemagglutination was greatly inhibited by polyrotaxanes with a certain threading % of alpha-CDs. Such an inhibitory effect was significantly superior to the other type of conjugates, in which poly(acrylic acid) was used as a backbone for maltose conjugation. The spin-spin relaxation time (T2) of the maltose C(1) proton in the polyrotaxane at a typical alpha-CD threading % was significantly larger than that of any other conjugate, which was well related to the inhibitory effect. Therefore, we concluded that the high mobility of maltose groups along the polyrotaxane structure contributes to enhanced Con A recognition.