Characterization of hydroxypropyl-beta-cyclodextrins used in the treatment of Niemann-Pick Disease type C1

Solving the puzzle of 2-hydroxypropyl β-cyclodextrin: Detailed assignment of the substituent distribution by NMR spectroscopy

2-Hydroxypropyl-β-cyclodextrin (HPBCD) is one of the most important cyclodextrin derivatives, finding extensive applications in the pharmaceutical sector. Beyond its role as an excipient, HPBCD achieved orphan drug status in 2015 for Niemann-Pick type C disease treatment, prompting research into its therapeutic potential for various disorders. However, the acceptance of HPBCD as an active pharmaceutical ingredient may be impeded by its complex nature. Indeed, HPBCD is not a single entity with a well-defined structure, instead, it is a complex mixture of isomers varying in substituent positions and the degree of hydroxypropylation, posing several challenges for unambiguous characterization. Pharmacopoeias' methods only address the average hydroxypropylation extent, lacking a rapid approach to characterize the substituent positions on the CD scaffold. Recognizing that the distribution of substituents significantly influences the complexation ability and overall activity of the derivative, primarily by altering cavity dimensions, we present a straightforward and non-destructive method based on liquid state NMR spectroscopy to analyze the positions of the hydroxypropyl sidechains. This method relies on a single set of routine experiments to establish quantitative assignment and it provides a simple yet effective tool to disclose the substitution pattern of this complex material, utilizing easily accessible (400 MHz NMR) instrumentation.

Cyclodextrins and derivatives in drug delivery: New developments, relevant clinical trials, and advanced products

Cyclodextrins (CD) and derivatives are functional excipients that can improve the bioavailability of numerous drugs. Because of their drug solubility improving properties they are used in many pharmaceutical products. Furthermore, the stability of small molecular drugs can be improved by the incorporation in CDs and an unpleasant taste and smell can be masked. In addition to well-established CD derivatives including hydroxypropyl-β-CD, hydroxypropyl-γ-CD, methylated- β-CD and sulfobutylated- β-CD, there are promising new derivatives in development. In particular, CD-based polyrotaxanes exhibiting cellular uptake enhancing properties, CD-polymer conjugates providing sustained drug release, enhanced cellular uptake, and mucoadhesive properties, and thiolated CDs showing mucoadhesive, in situ gelling, as well as permeation and cellular uptake enhancing properties will likely result in innovative new drug delivery systems. Relevant clinical trials showed various new applications of CDs such as the formation of CD-based nanoparticles, stabilizing properties for protein drugs or the development of ready-to-use injection systems. Advanced products are making use of various benefical properties of CDs at the same time. Within this review we provide an overview on these recent developments and take an outlook on how this class of excipients will further shape the landscape of drug delivery.

Hydroxypropyl-β-cyclodextrin inhibits the development of triple negative breast cancer by enhancing antitumor immunity

Triple negative breast cancer (TNBC) is regarded as one of the most aggressive forms of breast cancer. Hydroxypropyl-β-cyclodextrin (HP-β-CD) has been used as a therapeutic agent for Niemann-Pick disease Type C (NPC). However, the exact actions and mechanisms of HP-β-CD on TNBC are not fully understood. To examine the influence of HP-β-CD on the proliferation and migration of TNBC cell lines, particularly 4T1 and MDA-MB-231 cells, a range of assays, including MTT, scratch, cell cycle, and clonal formation assays, were performed. Furthermore, the effectiveness of HP-β-CD in the treatment of TNBC was assessed in vivo using a 4T1 tumor-bearing BALB/c mouse model. We demonstrated the anti-proliferation and anti-migration effect of HP-β-CD on TNBC both in vitro and in vivo. High cholesterol diet can attenuate HP-β-CD-inhibited TNBC growth. Mechanistically, HP-β-CD reduced tumor cholesterol levels by increasing ABCA1 and ABCG1-mediated cholesterol reverse transport. HP-β-CD promoted the infiltration of T cells into the tumor microenvironment (TME) and improved exhaustion of CD8+ T cells via reducing immunological checkpoint molecules expression. Additionally, HP-β-CD inhibited the recruitment of tumor associated macrophages to the TME via reducing CCL2-p38MAPK-NF-κB axis. HP-β-CD also inhibited the epithelial mesenchymal transition (EMT) of TNBC cells mediated by the TGF-β signaling pathway. In summary, our study suggests that HP-β-CD effectively inhibited the proliferation and metastasis of TNBC, highlighting HP-β-CD may hold promise as a potential antitumor drug.

Different solubilizing ability of cyclodextrin derivatives for cholesterol in Niemann-Pick disease type C treatment

BACKGROUND

Niemann-Pick disease type C (NPC) is a fatal neurodegenerative disorder caused by abnormal intracellular cholesterol trafficking. Cyclodextrins (CDs), the most promising therapeutic candidates for NPC, but with concerns about ototoxicity, are cyclic oligosaccharides with dual functions of unesterified cholesterol (UC) shuttle and sink that catalytically enhance the bidirectional flux and net efflux of UC, respectively, between the cell membrane and the extracellular acceptors. However, the properties of CDs that regulate these functions and how they could be used to improve treatments for NPC are unclear.

METHODS

We estimated CD-UC complexation for nine CD derivatives derived from native α-, β-, and γ-CD with different cavity sizes, using solubility and molecular docking analyses. The stoichiometry and complexation ability of the resulting complexes were investigated in relation to the therapeutic effectiveness and toxicity of each CD derivative in NPC experimental models.

FINDINGS

We found that shuttle and sink activities of CDs are dependent on cavity size-dependent stoichiometry and substituent-associated stability of CD-UC complexation. The ability of CD derivatives to form 1:1 and 2:1 complexes with UC were correlated with their ability to normalize intracellular cholesterol trafficking serving as shuttle and with their cytotoxicity associated with cellular UC efflux acting as sink, respectively, in NPC model cells. Notably, the ability of CD derivatives to form an inclusion complex with UC was responsible for not only efficacy but ototoxicity, while a representative derivative without this ability negligibly affected auditory function, underscoring its preventability.

CONCLUSIONS

Our findings highlight the importance of strategies for optimizing the molecular structure of CDs to overcome this functional dilemma in the treatment of NPC.

2-Hydroxypropyl-β-Cyclodextrin Treatment Induces Modest Immune Activation in Healthy Rhesus Macaques

Experimental simian immunodeficiency virus (SIV) infection of Asian macaques is an excellent model for HIV disease progression and therapeutic development. Recent coformulations of nucleoside analogs and an integrase inhibitor have been used for parenteral antiretroviral (ARV) administration in SIV-infected macaques, successfully resulting in undetectable plasma SIV RNA. In a cohort of SIVmac239-infected macaques, we recently observed that administration of coformulated ARVs resulted in an unexpected increase in plasma levels of soluble CD14 (sCD14), associated with stimulation of myeloid cells. We hypothesized that the coformulation solubilizing agent Kleptose (2-hydroxypropyl-β-cyclodextrin [HPβCD]) may induce inflammation with myeloid cell activation and the release of sCD14. Herein, we stimulated peripheral blood mononuclear cells (PBMCs) from healthy macaques with HPβCD from different commercial sources and evaluated inflammatory cytokine production in vitro. Treatment of PBMCs resulted in increased sCD14 release and myeloid cell interleukin-1β (IL-1β) production-with stimulation varying significantly by HPβCD source-and destabilized lymphocyte CCR5 surface expression. We further treated healthy macaques with Kleptose alone. In vivo, we observed modestly increased myeloid cell activation in response to Kleptose treatment without significant perturbation of the immunological transcriptome or epigenome. Our results demonstrate a need for vehicle-only controls and highlight immunological perturbations that can occur when using HPβCD in pharmaceutical coformulations. IMPORTANCE SIV infection of nonhuman primates is the principal model system for assessing HIV disease progression and therapeutic development. HPβCD has recently been incorporated as a solubilizing agent in coformulations of ARVs in SIV-infected nonhuman primates. Although HPβCD has historically been considered inert, recent findings suggest that HPβCD may contribute to inflammation. Herein, we investigate the contribution of HPβCD to healthy macaque inflammation in vitro and in vivo. We observe that HPβCD causes an induction of sCD14 and IL-1β from myeloid cells in vitro and demonstrate that HPβCD stimulatory capacity varies by commercial source. In vivo, we observe modest myeloid cell activation in blood and bronchoalveolar lavage specimens absent systemic immune activation. From our findings, it is unclear whether HPβCD stimulation may improve or diminish immune reconstitution in ARV-treated lentiviral infections. Our results demonstrate a need for vehicle-only controls and highlight immunological perturbations that can occur when using HPβCD in pharmaceutical coformulations.

Cyclodextrins applied to the treatment of lysosomal storage disorders

Cyclodextrin (CD), a cyclic oligosaccharide, is a pharmaceutical additive that improves the solubility of hydrophobic compounds. Recent research has focused on the potential active pharmaceutical abilities of CD. Lysosomal storage diseases are inherited metabolic diseases characterized by lysosomal dysfunction and abnormal lipid storage. Niemann-Pick disease type C (NPC) is caused by mutations in cholesterol transporter genes (NPC1, NPC2) and is characterized by cholesterol accumulation in lysosomes. A biocompatible cholesterol solubilizer 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was recently used in NPC patients for compassionate use and in clinical trials. HP-β-CD is an attractive drug candidate for NPC; however, its adverse effects, such as ototoxicity, should be solved. In this review, we discuss the current use of HP-β-CD in basic and clinical research and discuss alternative CD derivatives that may outperform HP-β-CD, which should be considered for clinical use. The potential of CD therapy for the treatment of other lysosomal storage diseases is also discussed.

Effects of 6-O-α-maltosyl-β cyclodextrin on lipid metabolism in Npc1-deficient Chinese hamster ovary cells

Niemann-Pick disease Type C (NPC) is a lysosomal storage disorder caused by mutation of the NPC1/NPC2 genes, which ultimately results in the accumulation of unesterified cholesterol (UEC) in lysosomes, thereby inducing symptoms such as progressive neurodegeneration and hepatosplenomegaly. This study determines the effects of 6-O-α-maltosyl-β cyclodextrin (Mal-βCD) on lipid levels and synthesis in Npc1-deficient (Npc1-KO cells) and vehicle CHO cells. Compared to vehicle cells, Npc1-KO cells exhibited high level of UEC, and low levels of esterified cholesterols (ECs) and long-chain fatty acids (LCFAs). The difference in lipid levels between Npc1-KO and CHO cells was largely ameliorated by Mal-βCD administration. Moreover, the effects of Mal-βCD were reproduced in the lysosomes prepared from Npc1-KO cells. Stable isotope tracer analysis with extracellular addition of D4-deuterated palmitic acid (D4-PA) to Npc1-KO cells increased the synthesis of D4-deuterated LCFAs (D4-LCFAs) and D4-deuterated ECs (D4-ECs) in a Mal-βCD-dependent manner. Simultaneous addition of D6-deuterated UEC (D6-UEC) and D4-PA promoted the Mal-βCD-dependent synthesis of D6-/D4-ECs, consisting of D6-UEC and D4-PA, D4-deuterated stearic acid, or D4-deuterated myristic acid, in Npc1-KO cells. These results suggest that Mal-βCD helps to maintain normal lipid metabolism by restoring balance among UEC, ECs, and LCFAs through acting on behalf of NPC1 in Npc1-KO cells and may therefore be useful in designing effective therapies for NPC.

Fine-tuned cholesterol solubilizer, mono-6-O-α-D-maltosyl-γ-cyclodextrin, ameliorates experimental Niemann-Pick disease type C without hearing loss

Niemann-Pick disease type C (NPC) is a fatal disorder with abnormal intracellular cholesterol trafficking resulting in neurodegeneration and hepatosplenomegaly. A cyclic heptasaccharide with different degrees of substitution of 2-hydroxypropyl groups, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), acts as a strong cholesterol solubilizer and is under investigation for treating this disease in clinical trials, but its physicochemical properties and ototoxicity remain a concern. Here, we evaluated the potential of mono-6-O-α-maltosyl-γ-CD (G2-γ-CD), a single-maltose-branched cyclic octasaccharide with a larger cavity than HP-β-CD, for treating NPC. We identified that G2-γ-CD ameliorated NPC manifestations in model mice and showed lower ototoxicity in mice than HP-β-CD. To investigate the molecular mechanisms of action behind the differential ototoxicity of these CDs, we performed cholesterol solubility analysis, proton nuclear magnetic resonance spectroscopy, and molecular modeling, and estimated that the cholesterol inclusion mode of G2-γ-CD maintained solely the 1:1 inclusion complex, whereas that of HP-β-CD shifted to the highly-soluble 2:1 complex at higher concentrations. We predicted the associations of these differential complexations of CDs with cholesterol with the profile of disease attenuation and of the auditory cell toxicity using specific cell models. We proposed that G2-γ-CD can serve as a fine-tuned cholesterol solubilizer for treating NPC, being highly biocompatible and physicochemically suitable for clinical application.

Parkinson's Disease Phenotypes in Patient Neuronal Cultures and Brain Organoids Improved by 2-Hydroxypropyl-β-Cyclodextrin Treatment

Background

The etiology of Parkinson's disease (PD) is only partially understood despite the fact that environmental causes, risk factors, and specific gene mutations are contributors to the disease. Biallelic mutations in the phosphatase and tensin homolog (PTEN)‐induced putative kinase 1 (PINK1) gene involved in mitochondrial homeostasis, vesicle trafficking, and autophagy are sufficient to cause PD.

Objectives

We sought to evaluate the difference between controls' and PINK1 patients' derived neurons in their transition from neuroepithelial stem cells to neurons, allowing us to identify potential pathways to target with repurposed compounds.

Methods

Using two‐dimensional and three‐dimensional models of patients' derived neurons we recapitulated PD‐related phenotypes. We introduced the usage of midbrain organoids for testing compounds. Using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9), we corrected the point mutations of three patients' derived cells. We evaluated the effect of the selected compound in a mouse model.

Results

PD patient‐derived cells presented differences in their energetic profile, imbalanced proliferation, apoptosis, mitophagy, and a reduced differentiation efficiency to tyrosine hydroxylase positive (TH+) neurons compared to controls' cells. Correction of a patient's point mutation ameliorated the metabolic properties and neuronal firing rates as well as reversing the differentiation phenotype, and reducing the increased astrocytic levels. Treatment with 2‐hydroxypropyl‐β‐cyclodextrin increased the autophagy and mitophagy capacity of neurons concomitant with an improved dopaminergic differentiation of patient‐specific neurons in midbrain organoids and ameliorated neurotoxicity in a mouse model.

Conclusion

We show that treatment with a repurposed compound is sufficient for restoring the impaired dopaminergic differentiation of PD patient‐derived cells. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Conformational preferences of TEMPO type radicals in complexes with cyclodextrins revealed by a combination of EPR spectroscopy, induced circular dichroism and molecular modeling

Electron paramagnetic resonance (EPR) spectroscopy is the main tool for evidencing the formation of inclusion complexes of cyclodextrins with paramagnetic guests, based on changes in the EPR parameters. In-depth information on complexation can only be obtained by a combination of physico-chemical methods. Herein we report on the interaction of three TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl) type radicals with cyclodextrins by collecting and analysing data provided experimentally by EPR and circular dichroism spectroscopies and theoretically by density functional theory and molecular docking. The study focused on the pH influence on the complexation of three paramagnetic probes with cyclodextrins. The EPR spectra revealed that the type and protonation state of the substituent linked to the TEMPO structure influences the affinity of the paramagnetic group for the cyclodextrin cavity. Neutral radical species favour stronger association with cyclodextrins and inclusion of the nitroxide group into the cavity, especially in the case of 4-carboxy-TEMPO. Induced circular dichroism signals of neutral species varied in sign and intensity as a function of substituent and cyclodextrin type. Density functional theory and molecular docking results supported the experimental data regarding the conformational preferences of TEMPO radicals in complexes with cyclodextrins.

Quantifying the hygroscopic properties of cyclodextrin containing aerosol for drug delivery to the lungs

Aerosol dynamics is important to quantify in drug delivery to the lungs with the aim of delivering therapeutics to a target location and optimising drug efficacy. The macrocycle (2-hydroxypropyl)-β-cyclodextrin (2-HP-β-CD) is thought to alleviate symptoms associated with neurodegenerative diseases when inhaled but the hygroscopic response is not well understood. Here we measure the hygroscopic growth of individual aqueous aerosol containing 2-HP-β-CD in optical tweezers through analysis of morphology-dependent resonances arising in Raman spectra. Droplets are analysed in the size range of 3-5 μm in radius. The evolving radius and refractive index of each droplet are measured in response to change in relative humidity from 98-20% to determine mass and radius based hygroscopic growth factors, and compared with dynamic vapour sorption measurements. Bulk solution refractive index and density measurements were used in accordance with the self-consistent Lorenz-Lorentz rule to determine melt solute and droplet properties. The refractive index of 2-HP-β-CD was determined to be 1.520 ± 0.002 with a density of 1.389 ± 0.005 g cm^-3. To our knowledge, we show the first aerosol measurements of 2-HP-β-CD and determine hygroscopicity. By quantifying the hygroscopic growth and physicochemical properties of 2-HP-β-CD, the impact of aerosol dynamics can be accounted for in tailoring drug formulations and informing models used to predict drug deposition patterns within the respiratory system.

2-Hydroxypropyl-β-cyclodextrins and the Blood-Brain Barrier: Considerations for Niemann-Pick Disease Type C1

The rare, chronic, autosomal-recessive lysosomal storage disease Niemann-Pick disease type C1 (NPC1) is characterized by progressively debilitating and ultimately fatal neurological manifestations. There is an urgent need for disease-modifying therapies that address NPC1 neurological pathophysiology, and passage through the blood-brain barrier represents an important consideration for novel NPC1 drugs. Animal investigations of 2-hydroxypropyl-β-cyclodextrins (HPβCD) in NPC1 in mice demonstrated that HPβCD does not cross the blood-brain barrier in significant amounts but suggested a potential for these complex oligosaccharides to moderately impact CNS manifestations when administered subcutaneously or intraperitoneally at very high doses; however, safety concerns regarding pulmonary toxicity were raised. Subsequent NPC1 investigations in cats demonstrated far greater HPβCD efficacy at much lower doses when the drug was administered directly to the CNS. Based on this, a phase 1/2a clinical trial was initiated with intrathecal administration of a specific, wellcharacterized mixture of HPβCD, with a tightly controlled molar substitution specification and a defined molecular "fingerprint" of the different species. The findings were very encouraging and a phase 2b/3 clinical trial has completed enrollment and is underway. In addition, phase 1 clinical studies utilizing high-dose intravenous administration of a different HPβCD are currently recruiting. Independent studies are needed for each product to satisfactorily address questions of safety, efficacy, dosing, and route of administration. The outcomes cannot be assumed to be translatable between HPβCD products and/or routes of administration.

In Vitro and In Vivo Evaluation of 6-O-α-Maltosyl-β-Cyclodextrin as a Potential Therapeutic Agent Against Niemann-Pick Disease Type C

Niemann-Pick disease Type C (NPC) is a rare lysosomal storage disease characterized by the dysfunction of intracellular cholesterol trafficking with progressive neurodegeneration and hepatomegaly. We evaluated the potential of 6-O-α-maltosyl-β-cyclodextrin (G2-β-CD) as a drug candidate against NPC. The physicochemical properties of G2-β-CD as an injectable agent were assessed, and molecular interactions between G2-β-CD and free cholesterol were studied by solubility analysis and two-dimensional proton nuclear magnetic resonance spectroscopy. The efficacy of G2-β-CD against NPC was evaluated using Npc1 deficient Chinese hamster ovary (CHO) cells and Npc1 deficient mice. G2-β-CD in aqueous solution showed relatively low viscosity and surface activity; characteristics suitable for developing injectable formulations. G2-β-CD formed higher-order inclusion complexes with free cholesterol. G2-β-CD attenuated dysfunction of intercellular cholesterol trafficking and lysosome volume in Npc1 deficient CHO cells in a concentration dependent manner. Weekly subcutaneous injections of G2-β-CD (2.9 mmol/kg) ameliorated abnormal cholesterol metabolism, hepatocytomegaly, and elevated serum transaminases in Npc1 deficient mice. In addition, a single cerebroventricular injection of G2-β-CD (21.4 μmol/kg) prevented Purkinje cell loss in the cerebellum, body weight loss, and motor dysfunction in Npc1 deficient mice. In summary, G2-β-CD possesses characteristics favorable for injectable formulations and has therapeutic potential against in vitro and in vivo NPC models.

Synthesis of the Anionic Hydroxypropyl-β-cyclodextrin:Poly(decamethylenephosphate) Polyrotaxane and Evaluation of its Cholesterol Efflux Potential in Niemann-Pick C1 Cells

Niemann-Pick type C disease (NPC) is a lysosomal storage disease that is characterized by a progressive accumulation of unesterified cholesterol in the lysosomes leading to organ damage from cell dysfunction. Hydroxypropyl-β-cyclodextrin (HP-β-CD) is an attractive drug candidate for treating NPC, as it diminishes cholesterol accumulation in NPC cells. Systemic HP-β-CD treatment, however, is limited by rapid renal clearance. We designed a new anionic HP-β-CD polyrotaxane to act as a slow release formulation based on a polyalkylene phosphate core to improve the pharmacokinetics. The polyalkylene phosphate comprises hydrophobic decamethylene spacers linked by biodegradable anionic phosphodiester bonds. HP-β-CD was threaded onto this polymer first and α-CD afterwards to prevent burst release of the threaded HP-β-CD. Our findings show that HP-β-CD was slowly released from the watersoluble polyrotaxane over a 30 days period. The polyrotaxane provided persistently diminished cholesterol levels in NPC1 cells by 20% relative to untreated cells. These results demonstrate the therapeutic potential of this novel HP-β-CD polyrotaxane for the mobilization of aberrantly stored cholesterol in NPC1 cells.

Recent neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC

Niemann–Pick disease type C (NPC) is a rare autosomal recessive lysosomal storage disorder with extensive biological, molecular, and clinical heterogeneity. Recently, numerous studies have tried to shed light on the pathophysiology of the disease, highlighting possible disease pathways common to other neurodegenerative disorders, such as Alzheimer’s disease and frontotemporal dementia, and identifying possible candidate biomarkers for disease staging and response to treatment. Miglustat, which reversibly inhibits glycosphingolipid synthesis, has been licensed in the European Union and elsewhere for the treatment of NPC in both children and adults. A number of ongoing clinical trials might hold promise for the development of new treatments for NPC. The objective of the present work is to review and evaluate recent literature data in order to highlight the latest neuroimaging, neurophysiological, and neuropathological advances for the understanding of NPC pathophysiology. Furthermore, ongoing developments in disease-modifying treatments will be briefly discussed.

Cyclodextrins and Iatrogenic Hearing Loss: New Drugs with Significant Risk

Cyclodextrins are a family of cyclic oligosaccharides with widespread usage in medicine, industry and basic sciences owing to their ability to solubilize and stabilize guest compounds. In medicine, cyclodextrins primarily act as a complexing vehicle and consequently serve as powerful drug delivery agents. Recently, uncomplexed cyclodextrins have emerged as potent therapeutic compounds in their own right, based on their ability to sequester and mobilize cellular lipids. In particular, 2-hydroxypropyl-β-cyclodextrin (HPβCD) has garnered attention because of its cholesterol chelating properties, which appear to treat a rare neurodegenerative disorder and to promote atherosclerosis regression related to stroke and heart disease. Despite the potential health benefits, use of HPβCD has been linked to significant hearing loss in several species, including humans. Evidence in mice supports a rapid onset of hearing loss that is dose-dependent. Ototoxicity can occur following central or peripheral drug delivery, with either route resulting in the preferential loss of cochlear outer hair cells (OHCs) within hours of dosing. Inner hair cells and spiral ganglion cells are spared at doses that cause ~85% OHC loss; additionally, no other major organ systems appear adversely affected. Evidence from a first-to-human phase 1 clinical trial mirrors animal studies to a large extent, indicating rapid onset and involvement of OHCs. All patients in the trial experienced some permanent hearing loss, although a temporary loss of function can be observed acutely following drug delivery. The long-term impact of HPβCD use as a maintenance drug, and the mechanism(s) of ototoxicity, are unknown. β-cyclodextrins preferentially target membrane cholesterol, but other lipid species and proteins may be directly or indirectly involved. Moreover, as cholesterol is ubiquitous in cell membranes, it remains unclear why OHCs are preferentially susceptible to HPβCD. It is possible that HPβCD acts upon several targets—for example, ion channels, tight junctions (TJ), membrane integrity, and bioenergetics—that collectively increase the sensitivity of OHCs over other cell types.