Cyclodextrins promote protein aggregation posing risks for therapeutic applications

Change in the Kinetic Regime of Aggregation of Yeast Alcohol Dehydrogenase in the Presence of 2-Hydroxypropyl-β-cyclodextrin

Chemical chaperones are low-molecular-weight compounds that suppress protein aggregation. They can influence different stages of the aggregation process-the stage of protein denaturation, the nucleation stage and the stage of aggregate growth-and this may lead to a change in the aggregation kinetic regime. Here, the possibility of changing the kinetic regime in the presence of a chemical chaperone 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) was investigated for a test system based on the thermally induced aggregation of yeast alcohol dehydrogenase (yADH) at 56 °C. According to differential scanning calorimetry data, 2-HP-β-CD did not affect the stage of the protein molecule unfolding. Dynamic light scattering data indicated changes in the aggregation kinetics of yADH during the nucleation and aggregate growth stages in the presence of the chaperone. The analysis of kinetic curves showed that the order of aggregation with respect to protein (nc), calculated for the stage of aggregate growth, changed from nc = 1 to nc = 2 with the addition of 100 mM 2-HP-β-CD. The mechanism of 2-HP-β-CD action on the yADH thermal aggregation leading to a change in its kinetic regime of aggregation is discussed.

Cyclodextrins: Structural, Chemical, and Physical Properties, and Applications

Due to their unique structural, physical and chemical properties, cyclodextrins and their derivatives have been of great interest to scientists and researchers in both academia and industry for over a century. Many of the industrial applications of cyclodextrins have arisen from their ability to encapsulate, either partially or fully, other molecules, especially organic compounds. Cyclodextrins are non-toxic oligopolymers of glucose that help to increase the solubility of organic compounds with poor aqueous solubility, can mask odors from foul-smelling compounds, and have been widely studied in the area of drug delivery. In this review, we explore the structural and chemical properties of cyclodextrins that give rise to this encapsulation (i.e., the formation of inclusion complexes) ability. This review is unique from others written on this subject because it provides powerful insights into factors that affect cyclodextrin encapsulation. It also examines these insights in great detail. Later, we provide an overview of some industrial applications of cyclodextrins, while emphasizing the role of encapsulation in these applications. We strongly believe that cyclodextrins will continue to garner interest from scientists for many years to come, and that novel applications of cyclodextrins have yet to be discovered.

Force Field Parameterization for the Description of the Interactions between Hydroxypropyl-β-Cyclodextrin and Proteins

Cyclodextrins are cyclic oligosaccharides, widely used as drug carriers, solubilizers, and excipients. Among cyclodextrins, the functionalized derivative known as hydroxypropyl-β-cyclodextrin (HPβCD) offers several advantages due to its unique structural features. Its optimal use in pharmaceutical and medical applications would benefit from a molecular-level understanding of its behavior, as can be offered by molecular dynamics simulations. Here, we propose a set of parameters for all-atom simulations of HPβCD, based on the ADD force field for sugars developed in our group, and compare it to the original CHARMM36 description. Using Kirkwood-Buff integrals of binary HPβCD-water mixtures as target experimental data, we show that the ADD-based description results in a considerably improved prediction of HPβCD self-association and interaction with water. We then use the new set of parameters to characterize the behavior of HPβCD toward the different amino acids. We observe pronounced interactions of HPβCD with both polar and nonpolar moieties, with a special preference for the aromatic rings of tyrosine, phenylalanine, and tryptophan. Interestingly, our simulations further highlight a preferential orientation of HPβCD's hydrophobic cavity toward the backbone atoms of amino acids, which, coupled with a favorable interaction of HPβCD with the peptide backbone, suggest a propensity for HPβCD to denature proteins.

Complex Formation of Resorufin and Resazurin with Β-Cyclodextrins: Can Cyclodextrins Interfere with a Resazurin Cell Viability Assay?

Resazurin (or Alamar Blue) is a poorly fluorescent dye. During the cellular reduction of resazurin, its highly fluorescent product resorufin is formed. Resazurin assay is a commonly applied method to investigate viability of bacterial and mammalian cells. In this study, the interaction of resazurin and resorufin with β-cyclodextrins was investigated employing spectroscopic and molecular modeling studies. Furthermore, the influence of β-cyclodextrins on resazurin-based cell viability assay was also tested. Both resazurin and resorufin form stable complexes with the examined β-cyclodextrins (2.0–3.1 × 10³ and 1.3–1.8 × 10³ L/mol were determined as binding constants, respectively). Cells were incubated for 30 and 120 min and treated with resazurin and/or β-cyclodextrins. Our results suggest that cyclodextrins are able to interfere with the resazurin-based cell viability assay that presumably results from the following mechanisms: (1) inhibition of the cellular uptake of resazurin and (2) enhancement of the fluorescence signal of the formed resorufin.

HP-β-cyclodextrin as an inhibitor of amyloid-β aggregation and toxicity

Amyloid deposits of misfolded amyloid-β protein (Aβ) on neuronal cells are a pathological hallmark of Alzheimer's disease (AD). Prevention of the abnormal Aβ aggregation has been considered as a promising therapeutic strategy for AD treatment. To prevent reinventing the wheel, we proposed to search the existing drug database for other diseases to identify potential Aβ inhibitors. Herein, we reported the inhibitory activity of HP-β-cyclodextrin (HP-β-CD), a well-known sugar used in drug delivery, genetic vector, environmental protection and treatment of Niemann-Pick disease type C1 (NPC1), against Aβ1-42 aggregation and Aβ-induced toxicity, with the aim of adding a new function as a sugar-based Aβ inhibitor. Experimental data showed that HP-β-CD molecules were not only nontoxic to cells, but also greatly inhibited Aβ fibrillization and reduced Aβ-induced toxicity in a concentration-dependent manner. At an optimal molar ratio of Aβ : HP-β-CD = 1 : 2, HP-β-CD enabled the reduction of 60% of Aβ fibrils and increased the cell viability to 92%. Such concentration-dependent inhibitor capacity of HP-β-CD was likely attributed to several combined effects, including the enhancement of Aβ-HP-β-CD interactions, prevention of structural transition of Aβ peptides towards β-sheet structures, and reduction of self-aggregation of HP-β-CD. In parallel, molecular simulations further revealed the atomic details of HP-β-CD interacting with the Aβ oligomer, showing that HP-β-CD had a high tendency to interact with hydrophobic residues of Aβ in two β-strands and the N-terminal tail. More importantly, we identified that the inner hydrophobic cavity of HP-β-CD was a key active site for Aβ inhibition. Once the inner cavity of HP-β-CD was blocked by a small hydrophobic molecule of ferulic acid, HP-β-CD completely lost its inhibition capacity against Aβ. Given the already established pharmaceutical functions of HP-β-CD in drug delivery, our findings suggest that HP-β-CD has great potential to be designed as a sugar-based Aβ inhibitor.

Aminocyclodextrin Oligomers as Protective Agents of Protein Aggregation

Over 30 different amyloid proteins and a number of corresponding protein-misfolding diseases have been identified. Among these is Alzheimer's disease, the most common neurodegenerative disorder. The treatment of these diseases is still a goal to reach and many molecules have been studied in this context. Among these, the cyclodextrins have shown interesting potential as agents against protein aggregation (antiaggregants). On the basis of this interest, we investigated the effect on protein aggregation of some oligomers of β-cyclodextrins. In particular, it was found that amino oligomers show good inhibition of β-amyloid aggregation in the micromolar concentration range. The presence of both a multicavity system and amino groups seems to be essential for preventing protein aggregation.

Cyclodextrins as Protective Agents of Protein Aggregation: An Overview

Cyclodextrins are extensively used in different fields (e.g., catalysis, chromatography, pharma, supramolecular chemistry, bioorganic chemistry, and bioinorganic chemistry), and their applications have been widely reviewed. Their main application in the field of pharmaceutical is as a drug carrier. This review overviews, for the first time, the use of cyclodextrins and their derivatives as antiaggregant agents in a number of proteins (e.g., amyloid-β, insulin, recombinant human growth hormone, prion protein, transthyretin, and α-synuclein) and some multimeric enzymes. There are many diseases that are correlated to protein misfolding and amyloid formation processes affecting numerous organs and tissues. There are over 30 different amyloid proteins and a number of corresponding diseases. Alzheimer's disease is the most common neurodegenerative disease. Treatment of these diseases is still a goal to reach, and many molecules are studied in this perspective. Cyclodextrins have also been studied, and they show great potential; as such, further studies could be very promising. This review aims to be a stimulus for the design of new cyclodextrin derivatives to obtain multifunctional systems with antiaggregant activity.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.

β-cyclodextrin and curcumin, a potent cocktail for disaggregating and/or inhibiting amyloids: a case study with α-synuclein

Aggregation of α-synuclein has been implicated in Parkinson's disease (PD). While many compounds are known to inhibit α-synuclein aggregation, dissolution of aggregates into their constituent monomers cannot be readily achieved. In this study, using a range of techniques, we have shown that an optimized cocktail of curcumin and β-cyclodextrin, at appreciably low concentrations, not only inhibited aggregation but also broke up the preformed aggregates almost completely. We propose that these compounds exhibit synergy in their action and thus provide us with the exciting prospect of working toward the development of a suitable drug candidate for prevention and treatment of PD.

Diaminothiazoles modify Tau phosphorylation and improve the tauopathy in mouse models

Although Tau accumulation is a feature of several neurodegenerative conditions, treatment options for these conditions are nonexistent. Targeting Tau kinases represents a potential therapeutic approach. Small molecules in the diaminothiazole class are potent Tau kinase inhibitors that target CDK5 and GSK3β. Lead compounds from the series have IC50 values toward CDK5/p25 and GSK3β in the low nanomolar range and no observed toxicity in the therapeutic dose range. Neuronal protective effects and decreased PHF-1 immunoreactivity were observed in two animal models, 3×Tg-AD and CK-p25. Treatment nearly eliminated Sarkosyl-insoluble Tau with the most prominent effect on the phosphorylation at Ser-404. Treatment also induced the recovery of memory in a fear conditioning assay. Given the contribution of both CDK5/p25 and GSK3β to Tau phosphorylation, effective treatment of tauopathies may require dual kinase targeting.

Dye-binding assays for evaluation of the effects of small molecule inhibitors on amyloid (aβ) self-assembly

Dye-binding assays, such as those utilizing Congo red and thioflavin T, are among the most widely used tools to probe the aggregation of amyloidogenic biomolecules and for the evaluation of small molecule inhibitors of amyloid aggregation and fibrillization. A number of recent reports have indicated that these dye-binding assays could be prone to false positive effects when assessing inhibitors' potential toward Aβ peptides, species involved in Alzheimer's disease. Specifically, this review focuses on the application of thioflavin T for determining the efficiency of small molecule inhibitors of Aβ aggregation and addresses potential reasons that might be associated with the false positive effects in an effort to increase reliability of dye-binding assays.

Oxidative stress: a pathogenic mechanism for Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a neurovisceral atypical lipid storage disorder involving the accumulation of cholesterol and other lipids in the late endocytic pathway. The pathogenic mechanism that links the accumulation of intracellular cholesterol with cell death in NPC disease in both the CNS and the liver is currently unknown. Oxidative stress has been observed in the livers and brains of NPC mice and in different NPC cellular models. Moreover, there is evidence of an elevation of oxidative stress markers in the serumof NPC patients. Recent evidence strongly suggests that mitochondrial dysfunction plays an important role in NPC pathogenesis and that mitochondria could be a significant source of oxidative stress in this disease. In this context, the accumulation of vitamin E in the late endosomal/lysosomal compartments in NPC could lead to a potential decrease of its bioavailability and could be another possible cause of oxidative damage. Another possible source of reactive species in NPC is the diminished activity of different antioxidant enzymes. Moreover, because NPC is mainly caused by the accumulation of free cholesterol, oxidized cholesterol derivatives produced by oxidative stress may contribute to the pathogenesis of the disease.

Specific binding of a β-cyclodextrin dimer to the amyloid β peptide modulates the peptide aggregation process

Alzheimer's disease involves progressive neuronal loss. Linked to the disease is the amyloid β (Aβ) peptide, a 38-43-amino acid peptide found in extracellular amyloid plaques in the brain. Cyclodextrins are nontoxic, cone-shaped oligosaccharides with a hydrophilic exterior and a hydrophobic cavity making them suitable hosts for aromatic guest molecules in water. β-Cyclodextrin consists of seven α-d-glucopyranoside units and has been shown to reduce the level of fibrillation and neurotoxicity of Aβ. We have studied the interaction between Aβ and a β-cyclodextrin dimer, consisting of two β-cyclodextrin monomers connected by a flexible linker. The β-cyclodextrin monomer has been found to interact with Aβ(1-40) at sites Y10, F19, and/or F20 with a dissociation constant (K(D)) of 3.9 ± 2.0 mM. Here (1)H-(15)N and (1)H-(13)C heteronuclear single-quantum correlation nuclear magnetic resonance (NMR) spectra show that in addition, the β-cyclodextrin monomer and dimer bind to the histidines. NMR translational diffusion experiments reveal the increased affinity of the β-cyclodextrin dimer (apparent K(D) of 1.1 ± 0.5 mM) for Aβ(1-40) compared to that of the β-cyclodextrin monomer. Kinetic aggregation experiments based on thioflavin T fluorescence indicate that the dimer at 0.05-5 mM decreases the lag time of Aβ aggregation, while a concentration of 10 mM increases the lag time. The β-cyclodextrin monomer at a high concentration decreases the lag time of the aggregation. We conclude that cyclodextrin monomers and dimers have specific, modulating effects on the Aβ(1-40) aggregation process. Transmission electron microscopy shows that the regular fibrillar aggregates formed by Aβ(1-40) alone are replaced by a major fraction of amorphous aggregates in the presence of the β-cyclodextrin dimer.

Protein stabilization by cyclodextrins in the liquid and dried state

Aggregation is arguably the biggest challenge for the development of stable formulations and robust manufacturing processes of therapeutic proteins. In search of novel excipients inhibiting protein aggregation, cyclodextrins and their derivatives have been under examination for use in parenteral protein products since more than 20 years and significant research work has been accomplished highlighting the great potential of cyclodextrins as stabilizers of therapeutic proteins. Oftentimes, the potential of cyclodextrins to inhibit protein aggregation has been attributed to their capability to incorporate hydrophobic residues on aggregation-prone proteins or on their partially unfolded intermediates into the hydrophobic cavity. In addition, also other mechanisms besides or even instead of complex formation play a role in the stabilization mechanism, e.g. non-ionic surfactant-like effects. In this review a comprehensive overview of the available research work on the beneficial use of cyclodextrins and their derivatives in protein formulations, liquid as well as dried, is provided. The mechanisms of stabilization against different kinds of stress conditions, such as thermal or surface-induced, are discussed in detail.

Rab GTPases as regulators of endocytosis, targets of disease and therapeutic opportunities

Rab GTPases are well-recognized targets in human disease, although are underexplored therapeutically. Elucidation of how mutant or dysregulated Rab GTPases and accessory proteins contribute to organ specific and systemic disease remains an area of intensive study and an essential foundation for effective drug targeting. Mutation of Rab GTPases or associated regulatory proteins causes numerous human genetic diseases. Cancer, neurodegeneration and diabetes represent examples of acquired human diseases resulting from the up- or downregulation or aberrant function of Rab GTPases. The broad range of physiologic processes and organ systems affected by altered Rab GTPase activity is based on pivotal roles in responding to cell signaling and metabolic demand through the coordinated regulation of membrane trafficking. The Rab-regulated processes of cargo sorting, cytoskeletal translocation of vesicles and appropriate fusion with the target membranes control cell metabolism, viability, growth and differentiation. In this review, we focus on Rab GTPase roles in endocytosis to illustrate normal function and the consequences of dysregulation resulting in human disease. Selected examples are designed to illustrate how defects in Rab GTPase cascades alter endocytic trafficking that underlie neurologic, lipid storage, and metabolic bone disorders as well as cancer. Perspectives on potential therapeutic modulation of GTPase activity through small molecule interventions are provided.

Cyclodextrin induces calcium-dependent lysosomal exocytosis

Cyclodextrins (CDs) have long been used to manipulate cellular cholesterol levels both in vitro and in vivo, but their direct effects at a cellular level are not well characterized. Recently, CDs have garnered much interest because of their ability to clear stored cholesterol from Niemann Pick Type C (NPC) cells and markedly prolong the life of NPC1 disease mice. Here, we investigate the hypothesis that treatment with 2-hydroxypropyl- β-cyclodextrin (HPB-CD) stimulates lysosomal exocytosis in a calcium-enhanced manner. We propose that this exocytosis is the mechanism by which HPB-CD ameliorates the endolysosomal cholesterol storage phenotype in NPC cells. These findings have significant implications for the use of HPB-CD in biochemical assays and data interpretation as well as for their use for the treatment for NPC and other disorders.

Niemann-Pick type C pathogenesis and treatment: from statins to sugars

The isolation of the causative genes for Niemann-Pick type C disease, a panethnic lysosomal lipid storage disorder, has provided models of how sterols and other lipids such as glycosphingolipids traverse the membranes of eukaryotic cells. Unfortunately, these molecular advances have yet to reciprocate with a cure for this devastating neurodegenerative disorder where neuronal replenishment will most likely yield the greatest benefit. In the meantime, stabilizing treatment strategies based on the removal of presumably toxic metabolites are in place. For example, the small molecule inhibition of glucosylceramide synthase by miglustat limits ganglioside accumulation and is now the only approved treatment of Niemann-Pick type C. In addition, 2-hydroxypropyl-B-cyclodextrin, a lipid chelator, relieves the lysosomal to endoplasmic reticulum blockage and markedly increases the life expectancy of the murine model. Ultimately, these strategies, targeting the primary biochemical lesion in these cells, and others will likely be combined to provide a synergistic cocktail approach to treating this disease.

Effect of 2-hydroxypropyl-beta-cyclodextrin on thermal inactivation, denaturation and aggregation of glyceraldehyde-3-phosphate dehydrogenase from rabbit skeletal muscle

The effect of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on thermal aggregation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rabbit skeletal muscle at 45 degrees C has been studied using dynamic light scattering. In the presence of HP-beta-CD higher values of the rate of aggregation and larger aggregates were registered. The acceleration of GAPDH aggregation was due to destabilization of the enzyme molecule under the action of HP-beta-CD. This is evidenced by the data on thermal inactivation of GAPDH and differential scanning calorimetry.

Thermal stability and aggregation of creatine kinase from rabbit skeletal muscle. Effect of 2-hydroxypropyl-beta-cyclodextrin

Effect of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on thermal aggregation of creatine kinase from rabbit skeletal muscle (RMCK) at 48 degrees C has been studied using dynamic light scattering. An increase in the duration of the lag period on the kinetic curves of aggregation, registered as an increment of the light scattering intensity in time, has been observed in the presence of HP-beta-CD. It has been shown that the initial parts of the dependences of the hydrodynamic radius (R(h)) of the protein aggregates on time follow the exponential law. The reciprocal value of parameter t(2R) (t(2R) is the time interval over which the R(h) value is doubled) was used to characterize the rate of aggregation. A 10-fold decrease in the 1/t(2R) value was observed in the presence of 76mM HP-beta-CD. Judging from the data on the kinetics of RMCK inactivation and the data on differential scanning calorimetry of RMCK, HP-beta-CD does not affect the rate of RMCK unfolding.