Cyclodextrin sulfates: characterization as polydisperse and amorphous mixtures

Self-doped conducting polymers in biomedical engineering: Synthesis, characterization, current applications and perspectives

Recent studies willingly agree that conducting polymers (CPs) are attractive materials for biomedical engineering purposes, mainly because of their unique physicochemical characteristics combining electrical conductivity and high biocompatibility. Nevertheless, the applicability of CPs is restricted by their limited stability under physiological conditions, associated with a decrease in electrical conductivity upon dedoping. Accordingly, modifying chemical structure of CPs to exhibit a self-doping effect seems to be an appealing approach aimed to enhance their functionality. The aim of this review is to provide a current state-of-the-art in the research concerning self-doped CPs, particularly those with potential biomedical applications. After presenting a library of available structure modifications, we describe their physicochemical characteristics, focusing on achievable conductivities, electrochemical, optical and mechanical behaviour, as well as biological properties. To highlight high applicability of self-doped CPs in biomedical engineering, we elaborate on biomedical areas benefiting most from using this type of conducting materials.

Selective modifications at the different positions of cyclodextrins: a review of strategies

Cyclodextrins (CDs) are natural, nontoxic, and biodegradable macrocyclic oligosaccharides. As supramolecular hosts, CDs have numerous applications in many aspects. However, nonsubstituted CDs have the disadvantages of solubility, unspecific recognition sites, and weak interactions with guest molecules. Therefore, new CD-based derivatives are successfully designed, synthesized, and widely used in various fields. This contribution outlines the research progress in CD derivatives. In particular, this review emphasizes the synthesis and application of CDs modified through functionalization in definite positions, random substitution, and reconstruction of the skeleton. At the end of this review, a summary and future directions are presented.

Effects of Selected Anionic β-Cyclodextrins on Persistence of Blood Glucose Lowering by Insulin Glargine after Subcutaneous Injection to Rats

Insulin glargine is a synthetic long-acting insulin product used for patients with diabetes mellitus. In this study, to obtain the further desirable blood-glucose lowering profile of insulin glargine, we investigated the effects of β-cyclodextrin sulfate (Sul-β-CyD) and sulfobutylether β-cyclodextrin (SBE7-β-CyD) on physicochemical properties of insulin glargine and pharmacokinetics/pharmacodynamics of insulin glargine after subcutaneous injection to rats. Sul-β-CyD and SBE7-β-CyD increased solubility of insulin glargine. SBE7-β-CyD suppressed the formation of oligomer and enhanced the dissolution rate of insulin glargine from its precipitate, compared to that of Sul-β-CyD. Additionally, we revealed that after subcutaneous administration of an insulin glargine solution, SBE7-β-CyD, but not Sul-β-CyD, increased bioavailability and sustained the blood-glucose lowering effect, possibly due to the inhibitory effects of SBE7-β-CyD on the enzymatic degradation at the injection site. These results suggest that SBE7-β-CyD could be a useful excipient for sustained release of insulin glargine.

Cyclodextrin polysulphate protects articular cartilage in experimental lapine knee osteoarthritis

OBJECTIVE

To evaluate the in vivo chondroprotective effect of cyclodextrin polysulphate (CDPS) in a rabbit model of experimental osteoarthritis (OA).

DESIGN

Experimental OA was induced in rabbits by anterior cruciate ligament transection (ACLT). Forty-eight hours post-surgery, the rabbits were randomised into three treatment groups (n=15 in each group) and a sham-operated control group. The rabbits were either injected subcutaneously with saline, 0.25 mg/kg CDPS or 1 mg/kg CDPS once a week for a period of 12 weeks, and their weight was monitored as a parameter for their general status. The animals were then sacrificed for macroscopic and histological assessment of the knee joints.

RESULTS

At the lowest dose, CDPS treatment was unable to induce a significant improvement of cartilage degradation vs the saline control in the experimentally induced knee OA. However, subcutaneous injections of 1 mg/kg CDPS induced a marked inhibition (P<0.05) of osteophyte formation. Additionally, a significant reduction of cartilage degradation revealed an overall chondroprotective effect of CDPS at a concentration of 1 mg/kg. No significant effects on weight gain were noted.

CONCLUSIONS

Systemic administration of CDPS is able to protect cartilage in vivo and can therefore be considered as a chondroprotective agent with structure modifying capacities.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

Isolation and characterization of beta-cyclodextrin sulfates by preparative gradient polyacrylamide gel electrophoresis, capillary electrophoresis and electrospray ionization - mass spectrometry

A beta-cyclodextrin sulfate mixture has been fractionated using discontinuous gradient polyacrylamide gel electrophoresis. Semidry electrotransfer of the sample onto a positively charged nylon membrane and visualization of a portion of this membrane with Alcian blue stain showed multiple bands. The bands were cut from the remaining portion of the membrane and after washing with 8 M urea, the beta-cyclodextrin sulfate fractions were eluted with 2 M sodium chloride and dialyzed. Analysis of each fraction using high resolution analytical gradient polyacrylamide gel electrophoresis as well as capillary electrophoresis, using indirect detection, showed some of the fractions to be pure while others were mixtures. Each beta-cyclodextrin sulfate fraction was complexed with a basic synthetic peptide and analyzed by electrospray ionization mass spectrometry to define the mass of the components in each mixture and thereby to determine the purity of each sample.

Application of a beta-cyclodextrin sulfate-immobilized precolumn to selective on-line enrichment and separation of heparin-binding proteins by column-switching high-performance liquid chromatography

A column-switching high-performance liquid chromatography (HPLC) system which consisted of a beta-cyclodextrin (beta-CD) sulfate-immobilized hydrophilic vinyl-polymer gel precolumn and a reversed-phase analytical column was developed for the selective on-line enrichment and separation of heparin-binding proteins. Of 15 proteins investigated, 10 proteins having heparin-binding activity were retained on the beta-CD sulfate precolumn almost quantitatively, in contrast 5 proteins having no heparin-binding activity were not retained. Calibration graphs for basic fibroblast growth factor constructed at various sample volumes were nearly identical, indicating that the protein could be enriched by this system. The system was successfully used for the selective separation of lysozyme in egg white. The beta-CD sulfate-immobilized precolumn showed no loss of analytical performance over 2 years during which about 400 samples were analysed.

Synthesis and biological evaluation of 2-amino-2-deoxy- and 6-amino-6-deoxy-cyclomaltoheptaose polysulfates as synergists for angiogenesis inhibition

2-Amino-2-deoxy-cyclomaltoheptaose was prepared from beta-cyclodextrin perbenzoate [heptakis(2,3,6-tri-O-benzoyl)cyclomaltoheptaose] by a series of reactions including selective de-O-benzoylation at C-2 of one of the perbenzoylated D-glucopyranosyl moieties, oxidation to the 2-ulose derivative, oxime formation, and reduction to the 2-amino-2-deoxy-D-glucose moiety. This compound and 6-amino-6-deoxycyclomaltoheptaose accessible from beta-cyclodextrin through the known procedure were sulfated to give polysulfated aminocyclomaltoheptaose derivatives (3, 5). Employing beta-cyclodextrin polysulfate as a reference compound, the synergistic effects of 3 and 5 for cortexolone or angiogenesis inhibitory activity were examined by rabbit-corneal micropocket assay system. In contrast to the significant anti-angiogenesis activity of the beta-cyclodextrin polysulfate-cortexolone pair, neither 3 nor 5 showed any cooperative activity with cortexolone in the inhibition of basic FGF-induced angiogenesis.

Differential effects of sulfate and sulfobutyl ether of beta-cyclodextrin on erythrocyte membranes in vitro

The hemolytic activity of beta-cyclodextrin (beta-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of beta-CyD; the membrane disrupting abilities decreased in the order of beta-CyD > 2-hydroxypropyl-beta-CyD (HP-beta-CyD) > sulfobutyl-beta-CyD (SB-beta-CyD) >> beta-CyD sulfate (S-beta-CyD). Under pre-hemolytic concentrations, both beta-CyD and SB-beta-CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S-beta-CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S-beta-CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike beta-CyD, S-beta-CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three beta-CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB-beta-CyD and S-beta-CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent beta-CyD and HP-beta-CyD.

Aluminium beta-cyclodextrin sulphate as a stabilizer and sustained-release carrier for basic fibroblast growth factor

The water-insoluble aluminium salt of beta-cyclodextrin sulphate (Al.beta-CyD-Sul) was used as a stabilizer and sustained-release carrier for recombinant human basic fibroblast growth factor (bFGF). An adsorbate of bFGF with Al.beta-CyD-Sul was prepared by incubating the protein with a suspension of Al.beta-CyD-Sul in water. The mitogenic activity of bFGF released from the adsorbate, as indicated by the proliferation of kidney cells of baby hamster (BHK-21), was almost comparable with that of the intact bFGF. Al.beta-CyD-Sul significantly protected bFGF from proteolytic degradation by pepsin and alpha-chymotrypsin, compared with the water-soluble sodium salt. The in-vitro release of bFGF from the adsorbate was sustained in proportion to a rise in the ratio of Al.beta-CyD-Sul to the protein in the adsorbate. Of the bFGF preparations evaluated, the adsorbate of bFGF with Al.beta-CyD-Sul, when given subcutaneously to the rat, showed the most prominent increase in the formation of granulation tissues, due to the stabilization and slow-release of the mitogen. The limited data presented here suggest that the adsorbate of bFGF with Al.beta-CyD-Sul has a potent therapeutic efficacy for wound healing, and may be applicable to oral protein formulations for the treatment of intestinal mucosal erosions.

Safety of oral cyclodextrins: effects of hydroxypropyl cyclodextrins, cyclodextrin sulfates and cationic cyclodextrins on steroid balance in rats

Derivatives of beta-cyclodextrin differing in the length of a hydroxyalkyl substituent (CH2CH2OH, CH2CHOHCH3, CH2CHOHCH2CH2CH2CH3) or in the electrical charge of the substituents (SO4-, CH2CHOHCH2N(CH3)3+) and hydroxypropyl derivatives (CH2CHOHCH3) of alpha-, beta-, and gamma-cyclodextrin were compared, individually and in mixtures, as solubilizers of cholesterol. The most effective solubilizer proved to be hydroxypropyl derivatives of beta-cyclodextrin; beta-cyclodextrin sulfate (SO4-) was practically devoid of solubilizing activity. Oral administration of these cyclodextrin derivatives, some of which are both nondegradable and effective complexation agents for cholesterol and bile acids, nevertheless did not affect the conversion of [14C]acetic acid to [14C]-cholesterol in rat under the same conditions when another bile acid complexation agent, cholestyramine, increased that conversion. Thus, complexation of cholesterol and of bile acids by cyclodextrin derivatives, which is a significant and well-defined phenomenon in vitro, seems to have limited importance in terms of excretion of cholesterol from the gastrointestinal tract. It is proposed that various untoward effects observed after chronic large oral doses of hydroxypropyl beta-cyclodextrin are administered are not caused by an increased excretion of some vital lipophile or enzyme but are probably caused by solubilization and increased absorption of toxic contaminants of the ingested food.

Protective effects of cyclodextrin sulphates against gentamicin-induced nephrotoxicity in the rat

The effects of cyclodextrin sulphates on the development of rat renal dysfunction induced with gentamicin, an aminoglycoside antibiotic, were studied. Daily subcutaneous injection of gentamicin (100 mg kg-1, 14 days) developed nephrotoxicity in the rat as assessed by an increase in serum urea nitrogen and histopathological changes in the renal cortex. When cyclodextrin sulphates were given intraperitoneally at 300 mg kg-1 at 6 h intervals after gentamicin administration, they protected the rat against the drug-induced renal impairment, while the parent cyclodextrins were ineffective. Since post-administration of cyclodextrin sulphates did not reduce the total amount of gentamicin accumulated in the kidney, the protection may occur through interference with intracellular events leading from the drug accumulation to nephrotoxicity. These results suggest that cyclodextrin sulphates are particularly effective in preventing renal failure associated with aminoglycoside treatment.