Cyclodextrins and their uses: a review

Complexation Thermodynamics of Cyclodextrins.

Non-phagocytic eukaryotic cells can internalize particles <1 microm in size, encompassing pathogens, liposomes for drug delivery or lipoplexes applied in gene delivery. In the present study, we have investigated the effect of particle size on the pathway of entry and subsequent intracellular fate in non-phagocytic B16 cells, using a range of fluorescent latex beads of defined sizes (50-1000 nm). Our data reveal that particles as large as 500 nm were internalized by cells via an energy-dependent process. With an increase in size (50-500 nm), cholesterol depletion increased the efficiency of inhibition of uptake. The processing of the smaller particles was significantly perturbed upon microtubule disruption, while displaying a negligible effect on that of the 500 nm beads. Inhibitor and co-localization studies revealed that the mechanism by which the beads were internalized, and their subsequent intracellular routing, was strongly dependent on particle size. Internalization of microspheres with a diameter <200 nm involved clathrin-coated pits. With increasing size, a shift to a mechanism that relied on caveolae-mediated internalization became apparent, which became the predominant pathway of entry for particles of 500 nm in size. At these conditions, delivery to the lysosomes was no longer apparent. The data indicate that the size itself of (ligand-devoid) particles can determine the pathway of entry. The clathrin-mediated pathway of endocytosis shows an upper size limit for internalization of approx. 200 nm, and kinetic parameters may determine the almost exclusive internalization of such particles along this pathway rather than via caveolae.

Size-dependent internalization of particles via the pathways of clathrin-and caveolae-mediated endocytosis

The lack of safe and efficient gene-delivery methods is a limiting obstacle to human gene therapy. Synthetic gene-delivery agents, although safer than recombinant viruses, generally do not possess the required efficacy. In recent years, a variety of effective polymers have been designed specifically for gene delivery, and much has been learned about their structure–function relationships. With the growing understanding of polymer gene-delivery mechanisms and continued efforts of creative polymer chemists, it is likely that polymer-based gene-delivery systems will become an important tool for human gene therapy.

Design and development of polymers for gene delivery

The development of nonviral vectors for safe and efficient gene delivery has been gaining considerable attention recently. An ideal nonviral vector must protect the gene against degradation by nuclease in the extracellular matrix, internalize the plasma membrane, escape from the endosomal compartment, unpackage the gene at some point and have no detrimental effects. In comparison to viruses, nonviral vectors are relatively easy to synthesize, less immunogenic, low in cost, and have no limitation in the size of a gene that can be delivered. Significant progress has been made in the basic science and applications of various nonviral gene delivery vectors; however, the majority of nonviral approaches are still inefficient and often toxic. To this end, two nonviral gene delivery systems using either biodegradable poly(D,Llactide-co-glycolide) (PLG) nanoparticles or cell penetrating peptide (CPP) complexes have been designed and studied using A549 human lung epithelial cells. PLG nanoparticles were optimized for gene delivery by varying particle surface chemistry using different coating materials that adsorb to the particle surface during formation. A variety of cationic coating materials were studied and compared to more conventional surfactants used for PLG nanoparticle fabrication. Nanoparticles (~200 nm) efficiently encapsulated plasmids encoding for luciferase (80-90%) and slowly released the same for two weeks. After a delay, moderate levels of gene expression appeared at day 5 for certain positively charged PLG particles and gene expression was maintained for at least two weeks. In contrast, gene expression mediated by polyethyleneimine (PEI) ended at day 5. PLG particles were also significantly less

Nonviral Vectors for Gene Delivery

Cyclodextrin Drug Carrier Systems.

https://onlinelibrary.wiley.com/doi/pdf/10.1021/js960213f

Pharmaceutical applications of cyclodextrins. III. Toxicological issues and safety evaluation

Alpha-, beta- and gamma-cyclodextrins are cyclic hexamers, heptamers, and octamers of glucose, respectively, and thus are hydrophilic; nevertheless, they have the ability to solubilize lipids through the formation of molecular inclusion complexes. The volume of lipophilic space involved in the solubilization process increases with the number of glucose units in the cyclodextrin molecule and, consequently, cyclodextrins were found to have different effects on human erythrocytes: (a) in the induction of shape change from discocyte to spherocyte the potency was observed to be alpha greater than gamma, but with beta-cyclodextrin hemolysis occurred before the change was complete; (b) in the increase of fluorescence intensity of 1-anilinonaphthalene-8-sulfonate in cyclodextrin-pretreated membranes, the observed potency was beta much greater than gamma greater than alpha; (c) in the release of potassium and hemoglobin, the potency was beta greater than alpha greater than gamma. The potencies of cyclodextrin for solubilizing various components of erythrocytes were alpha greater than beta much greater than gamma for phospholipids, beta much greater than gamma greater than alpha for cholesterol and beta much greater than gamma greater than alpha for proteins. The solubilization potencies were derived from concentration/final-effect curves. The above processes occurred without entry of solubilizer into the membrane, since (a) beta-[14C]cyclodextrin did not bind to erythrocytes and (b) cyclodextrins did not enter the cholesterol monolayer. A study of the [3H]cholesterol in erythrocytes indicated that beta-cyclodextrin extracted this lipid from membrane into a new compartment located in the aqueous phase which could equilibrate rapidly with additional erythrocytes. Therefore, the effects of cyclodextrins differ from those of detergents which first incorporate themselves into membranes then extract membrane components into supramolecular micelles.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1989.tb15171.x

Differential effects of α‐, β‐ and γ‐cyclodextrins on human erythrocytes

We have developed an automated method for measuring high-density lipoprotein (HDL)-cholesterol in serum without prior separation, using polyethylene glycol (PEG)-modified enzymes and sulfated alpha-cyclodextrin. When cholesterol esterase and cholesterol oxidase enzymes were modified with PEG, they showed selective catalytic activities towards lipoprotein fractions, with the reactivity increasing in the order: low-density lipoprotein < very-low-density lipoprotein approximately chylomicron < HDL. In the presence of magnesium ions, alpha-cyclodextrin sulfate reduced the reactivity of cholesterol, especially in chylomicrons and very-low-density lipoprotein, without the need for precipitation of those lipoprotein fractions. The combination of PEG-modified enzymes with alpha-cyclodextrin sulfate provided selectivity for the determination of HDL-cholesterol in serum in the presence of a small amount of dextran sulfate without the need for precipitation of lipoprotein aggregates. The results of the HDL-cholesterol assayed in serum by this direct method correlated well with those obtained by precipitation-based methods and also that by an ultracentrifugation method.

Kaneto Uekama

Papers

Cyclodextrin Drug Carrier Systems.

Pharmaceutical applications of cyclodextrins. III. Toxicological issues and safety evaluation

Differential effects of α‐, β‐ and γ‐cyclodextrins on human erythrocytes

Direct measurement of high-density lipoprotein cholesterol in serum with polyethylene glycol-modified enzymes and sulfated alpha-cyclodextrin.

Cyclodextrin-based controlled drug release system.