Beta cyclodextrins bind, stabilize, and remove lipofuscin bisretinoids from retinal pigment epithelium

Lysosomal Targeting of β-Cyclodextrin

β-Cyclodextrin (β-CD) and derivatives are approved therapeutics in >30 clinical settings. β-CDs have also shown promise as therapeutics for treatment of some lysosomal storage disorders, such as Niemann-Pick disease type C, and other disease states which involve metabolite accumulation in the lysosome. In these cases, β-CD activity relies on transport to the lysosome, wherein it can bind hydrophobic substrate and effect extraction. The post-translational attachment of N-glycans terminated in mannose-6-phosphate (M6P) residues is the predominant method by which lysosomal enzymes are targeted to the lysosome. In this work we covalently attach a synthetic biantennary bis-M6P-terminated N-glycan to β-CD and study the effect of the added glycans in a mammalian cell line. The formation of a host guest complex with a Cy5 fluorophore allows study of both cellular internalisation and transport to the lysosome by fluorescence microscopy. Results indicate that the rates of both internalisation and lysosomal transport are increased by the attachment of M6P-glycans to β-CD, indicating that M6P-glycan conjugation may improve the therapeutic effectiveness of β-CD for the treatment of disorders involving hydrophobic metabolite accumulation in the lysosome.

2-Hydroxypropyl-β-cyclodextrin mitigates pathological changes in a mouse model of retinal cholesterol dyshomeostasis

CYP46A1 is a CNS-specific enzyme, which eliminates cholesterol from the brain and retina by metabolism to 24-hydroxycholesterol, thus contributing to cholesterol homeostasis in both organs. 2-Hydroxypropyl-β-cyclodextrin (HPCD), a Food and Drug Administration-approved formulation vehicle, is currently being investigated off-label for treatment of various diseases, including retinal diseases. HPCD was shown to lower retinal cholesterol content in mice but had not yet been evaluated for its therapeutic benefits. Herein, we put Cyp46a1^-/- mice on high fat cholesterol-enriched diet from 1 to 14 months of age (control group) and at 12 months of age, started to treat a group of these animals with HPCD until the age of 14 months. We found that as compared with mature and regular chow-fed Cyp46a1^-/- mice, control group had about 6-fold increase in the retinal total cholesterol content, focal cholesterol and lipid deposition in the photoreceptor-Bruch's membrane region, and retinal macrophage activation. In addition, aged animals had cholesterol crystals at the photoreceptor-retinal pigment epithelium interface and changes in the Bruch's membrane ultrastructure. HPCD treatment mitigated all these manifestations of retinal cholesterol dyshomeostasis and altered the abundance of six groups of proteins (genetic information transfer, vesicular transport, and cytoskeletal organization, endocytosis and lysosomal processing, unfolded protein removal, lipid homeostasis, and Wnt signaling). Thus, aged Cyp46a1^-/- mice on high fat cholesterol-enriched diet revealed pathological changes secondary to retinal cholesterol overload and supported further studies of HPCD as a potential therapeutic for age-related macular degeneration and diabetic retinopathy associated with retinal cholesterol dyshomeostasis.

Continuous Flow Synthesis of A2E Guided by Design of Experiments and High-Throughput Studies

N-Retinylidene-N-retinylethanolamine (A2E) is the most studied lipid bisretinoid. It forms lipofuscin deposits in the retinal pigment epithelium (RPE), causing vision impairment and blindness in eye conditions, such as Stargardt's disease, cone-rod dystrophy, Best's macular dystrophy, and potentially age-related macular degeneration. Synthetic A2E is often used for inducing the accumulation of lipofuscins within the lysosomes of RPE cells in culture as an in vitro surrogate of retinal lipofuscin buildup, providing insights into the mechanisms of these eye conditions. Many reports describing the use of synthetic A2E employ material that has been prepared using a one-pot reaction of all-trans-retinal (ATR) and ethanolamine at room temperature for 48 h. We have revisited this synthesis by performing a design of experiments (DoE) and high-throughput experimentation workflow that was tailored to identify the most productive combination of the variables (temperature, solvent, and reagent equivalences) for optimization of A2E yield. Our DoE findings revealed that the interaction of ethanolamine with acetic acid and ATR was pivotal for the formation of A2E in high yield, indicating that imine formation is the critical step in the reaction. Armed with these results, we were able to optimize the method using a microfluidic reactor system before upscaling those conditions for continuous flow synthesis of A2E. This revised method enabled a more efficient production of material, from a reaction time of 48 h to a residence time of 33 min, with an accompanying yield improvement from 49 to 78%. Furthermore, we implemented a simple method to evaluate the quality of the A2E produced using optical spectroscopy and LC-MS characteristics to assure that the biological properties observed with A2E samples are not confounded by the presence of oxidized impurities that are commonly present in conventional A2E samples.

Modulation of CD36-mediated lipid accumulation and senescence by vitamin E analogs in monocytes and macrophages

The CD36/FAT scavenger receptor/fatty acids transporter regulates cellular lipid accumulation important for inflammation, atherosclerosis, lipotoxicity, and initiation of cellular senescence. Here we compared the regulatory effects of the vitamin E analogs alpha-tocopherol (αT), alpha-tocopheryl phosphate (αTP), and αTP/βCD (a nanocarrier complex between αTP and β-cyclodextrin [βCD]) and investigated their regulatory effects on lipid accumulation, phagocytosis, and senescence in THP-1 monocytes and macrophages. Both, αTP and αTP/βCD inhibited CD36 surface exposition stronger than αT leading to more pronounced CD36-mediated events such as inhibition of DiI-labeled oxLDL uptake, phagocytosis of fluorescent Staphylococcus aureus bioparticles, and cell proliferation. When compared to βCD, the complex of αTP/βCD extracted cholesterol from cellular membranes with higher efficiency and was associated with the delivery of αTP to the cells. Interestingly, both, αTP and more so αTP/βCD inhibited lysosomal senescence-associated beta-galactosidase (SA-β-gal) activity and increased lysosomal pH, suggesting CD36-mediated uptake into the endo-lysosomal phagocytic compartment. Accordingly, the observed pH increase was more pronounced with αTP/βCD in macrophages whereas no significant increase occurred with αT, alpha-tocopheryl acetate (αTA) or βCD. In contrast to αT and αTA, the αTP molecule is di-anionic at neutral pH, but upon moving into the acidic endo-lysosomal compartment becomes protonated and thus is acting as a base. Moreover, it is expected to be retained in lysosomes since it still carries one negative charge, similar to lysosomotropic drugs. Thus, treatment with αTP or αTP/βCD and/or inhibition of conversion of αTP to αT as it occurs in aged cells may counteract CD36-mediated overlapping inflammatory, senescent, and atherosclerotic events.

Orange palpebral spots: A case presentation

Orange palpebral spots are described as bilateral, ovoid, poorly defined orange-yellow macules on the superior eyelid and are predominantly reported in Caucasian populations. Previous reports have found correlations with melatonin incontinence secondary to trauma, lipofuscin accumulation in patients with superficial fatty tissue and palpebral thinness, and vitamin E, carotenoid and beta-cryptoxanthin levels. We present, to our knowledge, the first case of orange palpebral spots reported in the United Kingdom, in a patient with a background of atopy, significant sun exposure, bilateral cataracts and retinal detachment. The 59-year-old male initially presented with a dorsal nasal lesion with the differential: basal cell/trichoblastic carcinoma. During his excisional Mohs surgery, bilateral orange-yellow discolourations of the superior palpebrae were noted. The history was not significant for consumption of dietary sources of pigmentation, such as carotenoids, xanthophylls and vitamin E – found in green leafy vegetables and nut oils, respectively. The age of onset was unknown. A diagnostic skin punch biopsy was suggestive of orange palpebral spots and showed thinning of the epidermis, high-situated superficial and mature fat cells, with minimal pigment incontinence and perivascular lymphocytic infiltration. In addition, solar elastoses were identified on histology. After review in our local clinic-pathological meeting and of the published literature, a diagnosis of orange palpebral spots was given. The pathogenesis of orange palpebral spots remains to be elucidated. The role of sun exposure as a contributing factor to the generation of orange palpebral spots is therefore discussed.

Removal of RPE lipofuscin results in rescue from retinal degeneration in a mouse model of advanced Stargardt disease: Role of reactive oxygen species

Accumulation of lipofuscin in the retinal pigment epithelium (RPE) is a hallmark of aging and is associated with retinal degeneration encountered in age-related macular degeneration (AMD) and Stargardt disease (SD). Currently, treatment for lipofuscin-induced retinal degeneration is unavailable. Here, we report that Remofuscin (INN: soraprazan, a tetrahydropyridoether small molecule) reverses lipofuscin accumulation in aged primary human RPE cells and is non-cytotoxic in aged SD mouse RPE cells in vitro. In addition, we show that the removal of lipofuscin after a single intravitreal injection of Remofuscin results in a rescue from retinal degeneration in a mouse model of advanced SD which is even accompanied by an amelioration of the retinal dysfunction. Finally, we demonstrate that the mechanism causing lipofuscinolysis may involve the reactive oxygen species generated via the presence of Remofuscin. These data suggest a possible therapeutic approach to untreatable lipofuscin-mediated diseases like AMD, SD and lipofuscinopathies in neurodegenerative diseases.

Programmed Synthesis of Hepta-Differentiated β-Cyclodextrin: 1 out of 117655 Arrangements

Cyclodextrin poly-functionalization has fueled progress in their use in multiple applications such as enzyme mimicry, but also in the polymer sciences, luminescence, as sensors or for biomedical applications. However, regioselective access to a given pattern of functions on β-cyclodextrin is still very limited. We uncover a new orienting group, the thioacetate, that expands the toolbox available for cyclodextrin poly-hetero-functionalization using diisobutylaluminum hydride (DIBAL-H) promoted debenzylation. The usefulness of this group is illustrated in the first synthesis of a precisely hepta-hetero-functionalized β-cyclodextrin. By way of comparison, a random hepta-functionalization would give 117655 different molecules. This synthesis is not simply the vain quest for the Holy Grail of CD hetero-functionalization, but it illustrates the versatility of the DIBAL-H oriented hetero-functionalization strategy, opening the way to a multitude of useful functionalization patterns for new practical applications.

Cytotoxicity of β-Cyclodextrins in Retinal Explants for Intravitreal Drug Formulations

Cyclodextrins (CDs) have been widely used as pharmaceutical excipients for formulation purposes for different delivery systems. Recent studies have shown that CDs are able to form complexes with a variety of biomolecules, such as cholesterol. This has subsequently paved the way for the possibility of using CDs as drugs in certain retinal diseases, such as Stargardt disease and retinal artery occlusion, where CDs could absorb cholesterol lumps. However, studies on the retinal toxicity of CDs are limited. The purpose of this study was to examine the retinal toxicity of different beta-(β)CD derivatives and their localization within retinal tissues. To this end, we performed cytotoxicity studies with two different CDs—2-hydroxypropyl-βCD (HPβCD) and randomly methylated β-cyclodextrin (RMβCD)—using wild-type mouse retinal explants, the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, and fluorescence microscopy. RMβCD was found to be more toxic to retinal explants when compared to HPβCD, which the retina can safely tolerate at levels as high as 10 mM. Additionally, studies conducted with fluorescent forms of the same CDs showed that both CDs can penetrate deep into the inner nuclear layer of the retina, with some uptake by Müller cells. These results suggest that HPβCD is a safer option than RMβCD for retinal drug delivery and may advance the use of CDs in the development of drugs designed for intravitreal administration.

Penetration, distribution, and elimination of remofuscin/soraprazan in Stargardt mouse eyes following a single intravitreal injection using pharmacokinetics and transmission electron microscopic autoradiography: Implication for the local treatment of Stargardt's disease and dry age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in older people in the developed world while Stargardt's disease (SD) is a juvenile macular degeneration and an orphan disease. Both diseases are untreatable and are marked by accumulation of lipofuscin advancing to progressive deterioration of the retinal pigment epithelium (RPE) and retina and subsequent vision loss till blindness. We discovered that a small molecule belonging to the tetrahydropyridoether class of compounds, soraprazan renamed remofuscin, is able to remove existing lipofuscin from the RPE. This study investigated the drug penetration, distribution, and elimination into the eyes of a mouse model for increased lipofuscinogenesis, following a single intravitreal injection. We measured the time course of concentrations of remofuscin in different eye tissues using high-performance liquid chromatography combined with mass spectroscopy (HPLC-MS). We also visualized the penetration and distribution of 3 H-remofuscin in eye sections up to 20 weeks post-injection using transmission electron microscopic (TEM) autoradiography. The distribution of silver grains revealed that remofuscin accumulated specifically in the RPE by binding to the RPE pigments (melanin, lipofuscin and melanolipofuscin) and that it was still detected after 20 weeks. Importantly, the melanosomes in choroidal melanocytes only rarely bind remofuscin emphasizing its potential to serve as an active ingredient in the RPE for the treatment of SD and dry AMD. In addition, our study highlights the importance of electron microscopic autoradiography as it is the only method able to show drug binding with a high intracellular resolution.

Reversing cytotoxicity of uric acid by supramolecular encapsulation with acyclic cucurbit[n]uril

Supramolecular encapsulation removes harmful substances from organisms has evolved into a new strategy. In this article, we prepared three supramolecular complexes of acyclic cucurbit[n]urils (ACBs) with uric acid (UA), and studied the inclusion behaviors of ACBs and UA by fluorescence spectroscopy, UV-vis spectroscopy and nuclear magnetic resonance. Furthermore, we characterized the effect of the complexes of UA with ACBs on the expression of inflammatory biomarkers in human hepatoma HepG2 cell lines through C-reactive protein (CRP) western blot. The results showed UA molecules can be recognized by three ACBs with different binding constants, and ACBs successfully blocked the inflammatory stimulation of uric acid on HepG2 cell lines and inhibited the expression of the major inflammatory factor CRP by formations of complexes between UA and ACBs. This article proves that ACBs can efficiently reversing cytotoxicity of UA, which provides a new method to treating hyperuricemia disease.

Supramolecular hosts as in vivo sequestration agents for pharmaceuticals and toxins

Pharmaceutical agents, drugs of abuse, and toxic substances have a large impact, positive and negative, on modern society. Efforts to mitigate the side effects of pharmaceuticals and counteract the life threatening effects of drugs of abuse and toxins can occur either by pharmacodynamic (PD) approaches based on bioreceptor·drug antagonism or by pharmacokinetic (PK) approaches that seek to reduce the concentration of free drug. In this tutorial review, we present the use of supramolecular hosts (cyclodextrins, calixarenes, (acyclic) cucurbiturils, and pillararenes) as in vivo sequestration agents for neuromuscular blockers, drugs of abuse (methamphetamine and fentanyl), anesthetics, neurotoxins, the pesticide paraquat, and heparin anti-coagulants by the PK approach. The review presents the basic physical and molecular recognition features of the supramolecular hosts and some of the principles used in their selection and structural optimization for in vivo sequestration applications. The influence of host·guest complexation on other relevant in vivo properties of drugs (e.g. distribution, circulation time, excretion, redox properties) is also mentioned. The article concludes with a discussion of future directions.

Sequestration of pyridinium herbicides in plants by carboxylated pillararenes possessing different alkyl chains

We report that the sequestration of pyridinium-containing herbicides can be achieved on plant foliage through the strong supramolecular complexation with water-soluble pillararenes. The host–guest interaction appears to exert a protective effect on the plant growth, thus holding great promise in agricultural application.

We report that the sequestration of pyridinium-containing herbicides can be achieved on plant foliage through the strong supramolecular complexation with water-soluble pillararenes.

2-Hydroxypropyl-β-cyclodextrin reduces retinal cholesterol in wild-type and Cyp27a1-/- Cyp46a1-/- mice with deficiency in the oxysterol production

BACKGROUND AND PURPOSE

2-Hydroxypropyl-β-cyclodextrin (HPCD) is an FDA approved vehicle for drug delivery and an efficient cholesterol-lowering agent. HPCD was proposed to lower tissue cholesterol via multiple mechanisms including those mediated by oxysterols. CYP27A1 and CYP46A1 are the major oxysterol-producing enzymes in the retina that convert cholesterol to 27- and 24-hydroxycholesterol, respectively. We investigated whether HPCD treatments affected the retina of wild-type and Cyp27a1^-/- Cyp46a1^-/- mice that do not produce the major retinal oxysterols.

EXPERIMENTAL APPROACH

HPCD administration was either by i.p., p.o. or s.c. Delivery to the retina was confirmed by angiography using the fluorescently labelled HPCD. Effects on the levels of retinal sterols, mRNA and proteins were evaluated by GC-MS, qRT-PCR and label-free approach, respectively.

KEY RESULTS

In both wild-type and Cyp27a1^-/- Cyp46a1^-/- mice, HPCD crossed the blood-retinal barrier when delivered i.p. and lowered the retinal cholesterol content when administered p.o. and s.c. In both genotypes, oral HPCD treatment affected the expression of cholesterol-related genes as well as the proteins involved in endocytosis, lysosomal function and lipid homeostasis. Mechanistically, liver X receptors and the altered expression of Lipe (hormone-sensitive lipase), Nceh1 (neutral cholesterol ester hydrolase 1) and NLTP (non-specific lipid-transfer protein) could mediate some of the HPCD effects.

CONCLUSIONS AND IMPLICATIONS

HPCD treatment altered retinal cholesterol homeostasis and is a potential therapeutic approach for the reduction of drusen and subretinal drusenoid deposits, cholesterol-rich lesions and hallmarks of age-related macular degeneration.

LINKED ARTICLES

This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

The Diverse Roles of TIMP-3: Insights into Degenerative Diseases of the Senescent Retina and Brain

Tissue inhibitor of metalloproteinase-3 (TIMP-3) is a component of the extracellular environment, where it mediates diverse processes including matrix regulation/turnover, inflammation and angiogenesis. Rare TIMP-3 risk alleles and mutations are directly linked with retinopathies such as age-related macular degeneration (AMD) and Sorsby fundus dystrophy, and potentially, through indirect mechanisms, with Alzheimer's disease. Insights into TIMP-3 activities may be gleaned from studying Sorsby-linked mutations. However, recent findings do not fully support the prevailing hypothesis that a gain of function through the dimerisation of mutated TIMP-3 is responsible for retinopathy. Findings from Alzheimer's patients suggest a hitherto poorly studied relationship between TIMP-3 and the Alzheimer's-linked amyloid-beta (A) proteins that warrant further scrutiny. This may also have implications for understanding AMD as aged/diseased retinae contain high levels of A. Findings from TIMP-3 knockout and mutant knock-in mice have not led to new treatments, particularly as the latter does not satisfactorily recapitulate the Sorsby phenotype. However, recent advances in stem cell and in vitro approaches offer novel insights into understanding TIMP-3 pathology in the retina-brain axis, which has so far not been collectively examined. We propose that TIMP-3 activities could extend beyond its hitherto supposed functions to cause age-related changes and disease in these organs.

[Intracellularly Degradable Polyrotaxanes for Therapeutic Applications]

Recently, the application of β-cyclodextrins (β-CDs) as therapeutic agents has received considerable attention. β-CDs have been reported to have therapeutic effects on various diseases, such as Niemann-Pick type C (NPC) disease, a family of lysosomal storage disorders characterized by the lysosomal accumulation of cholesterol. To further improve the therapeutic efficacy of β-CDs, the use of β-CD-threaded polyrotaxanes (PRXs) has been proposed as a carrier of β-CDs for NPC disease. PRXs are supramolecular polymers composed of many CDs threaded onto a linear polymer chain and capped with bulky stopper molecules. In this review, the design of PRXs and their therapeutic applications are described. To achieve the intracellular release of threaded β-CDs from PRXs, stimuli-cleavable linkers are introduced in an axle polymer of PRXs. The stimuli-labile PRXs can dissociate into their constituent molecules by a cleavage reaction under specific stimuli, such as pH reduction in lysosomes. The release of the threaded β-CDs from acid-labile PRXs in acidic lysosomes leads to the formation of an inclusion complex with the cholesterol that has accumulated in NPC disease patient-derived fibroblasts, thus promoting the extracellular excretion of the excess cholesterol. Moreover, the administration of PRXs to a mouse model of NPC disease caused significant suppression of the tissue accumulation of cholesterol, resulting in a prolonged life span in the model mice. Additionally, the induction of autophagy by the methylated β-CD-threaded PRXs (Me-PRXs) is described. Accordingly, the stimuli-labile PRXs are expected to be effective carriers of CDs for therapeutic applications.

Reaction kinetics of a water-soluble palladium–β-cyclodextrin catalyst for a Suzuki–Miyaura cross-coupling in continuous flow

An experimental and theoretical investigation on the reaction kinetics of a Suzuki–Miyaura cross-coupling catalyzed using the Pd–β-cyclodextrin ligand in continuous flow.

Quercetin-3-O-α-l-arabinopyranoside protects against retinal cell death via blue light-induced damage in human RPE cells and Balb-c mice

Age-related macular degeneration (AMD) is among the increasing number of diseases causing irreversible blindness in the elderly. Dry AMD is characterized by the accumulation of lipofuscin in retinal pigment epithelium (RPE) cells. N-Retinylidene-N-retinylethanolamine (A2E), a component of lipofuscin, is oxidized to oxo-A2E under blue light illumination, leading to retinal cell death. The aim of this study was to investigate the protective effect and mechanism of quercetin-3-O-α-l-arabinopyranoside (QA) against blue light (BL)-induced damage in both RPE cells and mice models. Treatment by QA inhibited A2E uptake in RPE cells, as determined by a decrease in fluorescence intensity. QA also protected A2E-laden RPE cells against BL-induced apoptosis. QA inhibited C3 complement activation and poly (ADP-ribose) polymerase (PARP) cleavage, as determined by western blotting. QA showed an inhibitory effect on AP1 and NF-kB activity as estimated in a reporter gene assay. In addition, QA activated the gene expression of aryl hydrocarbon receptor target genes (CYP1A1, CYP1B1) in TCDD-treated RPE cells. In the mice model, oral administration of QA protected against retinal degeneration induced by BL exposure as determined by histological analyses (thickness of retinal layers and immunostaining for caspase-3). In addition, QA inhibited apoptosis and inflammation via inhibition of NF-kB p65 translocation, C3 activation, and PARP cleavage. Collectively, these results revealed the protective mechanism of QA against BL-induced retinal damage both in vitro and in vivo.

Polyrotaxane-based systemic delivery of β-cyclodextrins for potentiating therapeutic efficacy in a mouse model of Niemann-Pick type C disease

Niemann-Pick type C (NPC) disease is a fatal metabolic disorder characterized by the lysosomal accumulation of cholesterol. Although 2-hydroxypropyl β-cyclodextrin (HP-β-CD) promotes the excretion of cholesterol and prolongs the life span in animal models of NPC disease, it requires extremely high dose. We developed acid-labile β-CD-based polyrotaxanes (PRXs) comprising multiple β-CDs threaded along a polymer chain capped with acid-cleavable stopper molecules for potentiating therapeutic efficacy of β-CD in NPC disease. The acid-labile PRXs dissociate under the acidic lysosomes and release threaded β-CDs in lysosomes, which promotes cholesterol excretion in NPC disease model cells at lower concentration than HP-β-CD. In this study, the therapeutic effect of the PRXs in a mouse model of NPC disease was investigated. Weekly administration of the PRXs significantly prolonged the life span and suppressed neurodegeneration in mice, even at a dose of 500mg/kg, a markedly lower dose than previously reported for HP-β-CD. Detailed analysis of tissue cholesterol revealed that PRX treatment markedly suppressed the tissue accumulation of cholesterol in the NPC mouse model, but did not alter cholesterol content in wild-type mice. Acid-labile PRX is therefore a promising candidate for potentiating the efficacy of β-CD in the treatment of NPC disease.

Acid-Induced Intracellular Dissociation of β-Cyclodextrin-Threaded Polyrotaxanes Directed toward Attenuating Phototoxicity of Bisretinoids through Promoting Excretion

In the retinal pigment epithelium of patients with age-related macular degeneration (AMD), excess N-retinylidene-N-retinylethanolamine (A2E), a dimer of all-trans-retinal, accumulats to induce inflammatory cytokine secretion and phototoxic effects. Therefore, the reduction of intracellular A2E is a promising approach for the prevention and treatment of AMD. In this study, acid-labile β-cyclodextrin (β-CD)-threaded polyrotaxanes (PRXs) were synthesized and investigated their effects on the removal of A2E accumulated in retinal pigment epithelium cells (ARPE-19) in comparison to nonlabile PRXs and 2-hydroxypropyl β-CD (HP-β-CD) were examined. GC-MS and HPLC studies strongly suggest that the acid-labile PRXs dissociated into their constituent molecules in cells by lysosomal acidification and threaded β-CDs were considered to be released from the PRXs. The released β-CDs formed an inclusion complex with A2E, which promoted the excretion of A2E. Indeed, the acid-labile PRXs effectively reduced intracellular A2E level at approximately a 10-fold lower concentration than HP-β-CD. Accompanied with A2E removal, the toxicity and phototoxicity of A2E were attenuated by treatment with acid-labile PRXs. Because the nonlabile PRX failed to reduce intracellular A2E level and attenuate phototoxicity, intracellular release of threaded β-CDs from the acid-labile PRX might contribute to reducing intracellular A2E. We conclude that acid-labile PRXs are promising candidates for the treatment of macular diseases through the removal of toxic metabolites.

2-Hydroxypropyl-beta-cyclodextrin (HPβCD) reduces age-related lipofuscin accumulation through a cholesterol-associated pathway

Oxidative stress causes significant increases in both cholesterol uptake and intracellular accumulation of the aging biomarker lipofuscin. Here we show that HPβCD addition mitigates these adverse effects in human fibroblasts by significantly reducing LDLr and SREBP1 gene expression. In the absence of oxidative stress, HPβCD addition induces a paradoxical response, increasing cholesterol accumulation (but not lipofuscin) via upregulation of cholesterol biosynthesis. These two distinct, but opposite effects highlight a previously overlooked therapeutic consideration: the cholesterol content of the treated cell determines which cholesterol pathways, either beneficial or harmful, are responsive to HPβCD.

Autophagy Regulates Proteasome Inhibitor-Induced Pigmentation in Human Embryonic Stem Cell-Derived Retinal Pigment Epithelial Cells

The impairment of autophagic and proteasomal cleansing together with changes in pigmentation has been documented in retinal pigment epithelial (RPE) cell degeneration. However, the function and co-operation of these mechanisms in melanosome-containing RPE cells is still unclear. We show that inhibition of proteasomal degradation with MG-132 or autophagy with bafilomycin A1 increased the accumulation of premelanosomes and autophagic structures in human embryonic stem cell (hESC)-derived RPE cells. Consequently, upregulation of the autophagy marker p62 (also known as sequestosome-1, SQSTM1) was confirmed in Western blot and perinuclear staining. Interestingly, cells treated with the adenosine monophosphatedependent protein kinase activator, AICAR (5-Aminoimidazole-4-carboxamide ribonucleotide), decreased the proteasome inhibitor-induced accumulation of premelanosomes, increased the amount of autophagosomes and eradicated the protein expression of p62 and LC3 (microtubule-associated protein 1A/1B-light chain 3). These results revealed that autophagic machinery is functional in hESC-RPE cells and may regulate cellular pigmentation with proteasomes.

Cyclodextrin has conflicting actions on autophagy flux in vivo in brains of normal and Alzheimer model mice

2-hydroxypropyl-β-cyclodextrin (CYCLO), a modifier of cholesterol efflux from cellular membrane and endo-lysosomal compartments, reduces lysosomal lipid accumulations and has therapeutic effects in animal models of Niemann-Pick disease type C and several other neurodegenerative states. Here, we investigated CYCLO effects on autophagy in wild-type mice and TgCRND8 mice-an Alzheimer's Disease (AD) model exhibiting β-amyloidosis, neuronal autophagy deficits leading to protein and lipid accumulation within greatly enlarged autolysosomes. A 14-day intracerebroventricular administration of CYCLO to 8-month-old TgCRND8 mice that exhibit moderately advanced neuropathology markedly diminished the sizes of enlarged autolysosomes and lowered their content of GM2 ganglioside and Aβ-immunoreactivity without detectably altering amyloid precursor protein processing or extracellular Aβ/β-amyloid burden. We identified two major actions of CYCLO on autophagy underlying amelioration of lysosomal pathology. First, CYCLO stimulated lysosomal proteolytic activity by increasing cathepsin D activity, levels of cathepsins B and D and two proteins known to interact with cathepsin D, NPC1 and ABCA1. Second, CYCLO impeded autophagosome-lysosome fusion as evidenced by the accumulation of LC3, SQSTM1/p62, and ubiquitinated substrates in an expanded population of autophagosomes in the absence of greater autophagy induction. By slowing substrate delivery to lysosomes, autophagosome maturational delay, as further confirmed by our in vitro studies, may relieve lysosomal stress due to accumulated substrates. These findings provide in vivo evidence for lysosomal enhancing properties of CYCLO, but caution that prolonged interference with cellular membrane fusion/autophagosome maturation could have unfavorable consequences, which might require careful optimization of dosage and dosing schedules.

Reversing the Cytotoxicity of Bile Acids by Supramolecular Encapsulation

Supramolecular encapsulation has been developed into a powerful tool in clearance of toxic substances and hazardous waste from living body and external environments. Herein we tested the special efficacy of tyramine-modified β-cyclodextrin (1) in inhibiting and reversing of the inherent cytotoxicity of deoxycholic acid (DCA). The decarboxylation from tyrosine to tyramine in 1 is crucial to the mutual electrostatic communication, ultimately leading to great enhancement in binding affinity and molecular selectivity toward bile acids. As a result, the DCA-mediated cytotoxicity could be largely eliminated by the biocompatible 1. Meanwhile, the excess DCA could be rapidly excreted by 1 via rat urinary clearance, thus facilitating the decrease of DCA concentration in blood. This study presents a proof of principle that the supramolecular encapsulation with functional cyclodextrin derivatives can efficiently modulate the cell progression and remove the cytotoxic DCA, which provides a practical approach to prevent or treat bile acid-involved diseases.

Oligo(ethylene glycol)-modified β-cyclodextrin-based polyrotaxanes for simultaneously modulating solubility and cellular internalization efficiency

We developed stimuli-labile polyrotaxanes (PRXs) composed of β-cyclodextrin (β-CD), Pluronic as an axle polymer, and acid-cleavable N-triphenylmethyl groups as bulky stopper molecules, and found that the PRXs are potent therapeutics for Niemann-Pick type C disease, because the PRX can effectively reduce intracellular cholesterol through the intracellular release of threaded β-CDs. In general, the PRXs need to be chemically modified with hydrophilic functional groups because PRXs are not soluble in aqueous media. Herein, four series of oligo(ethylene glycol)s (OEGs) with different ethylene glycol repeating unit (2 or 3) and chemical structure of OEG terminal (hydroxy or methoxy) were modified onto the threaded β-CDs in PRX. The effects of the structure of OEG on the aqueous solubility, toxicity, and cellular internalization efficiency of OEG-modified PRXs were investigated to optimize the chemical structure of OEG. The hydroxy-terminated OEG-modified PRXs showed excellent solubility in aqueous media and no toxicity, regardless of the number of ethylene glycol repeating units. In the case of the methoxy-terminated OEG-modified PRXs, sufficient solubility in aqueous media and negligible toxicity were observed when the number of ethylene glycol repeating units was 3, while low solubility and toxicity were observed when the ethylene glycol repeating unit was 2. Additionally, cellular uptake levels of methoxy-terminated OEG-modified PRXs in RAW264.7 cells were higher than those of hydroxy-terminated OEG-modified PRXs. Consequently, the chemical structure of the OEG strongly affects the chemical and biological properties of the PRXs, and that a methoxy-terminated OEG with 3 ethylene glycol repeating units is the most preferable modification of PRXs, since the resultant PRX is sufficiently soluble in aqueous media, non-toxic, and possesses high cellular internalization efficiency.

Norbixin Protects Retinal Pigmented Epithelium Cells and Photoreceptors against A2E-Mediated Phototoxicity In Vitro and In Vivo

The accumulation of N-retinylidene-N-retinylethanolamine (A2E, a toxic by-product of the visual pigment cycle) in the retinal pigment epithelium (RPE) is a major cause of visual impairment in the elderly. Photooxidation of A2E results in retinal pigment epithelium degeneration followed by that of associated photoreceptors. Present treatments rely on nutrient supplementation with antioxidants. 9’-cis-Norbixin (a natural diapocarotenoid, 97% purity) was prepared from Bixa orellana seeds. It was first evaluated in primary cultures of porcine retinal pigment epithelium cells challenged with A2E and illuminated with blue light, and it provided an improved photo-protection as compared with lutein or zeaxanthin. In Abca4^-/-Rdh8^-/- mice (a model of dry AMD), intravitreally-injected norbixin maintained the electroretinogram and protected photoreceptors against light damage. In a standard rat blue-light model of photodamage, norbixin was at least equally as active as phenyl-N-tert-butylnitrone, a free radical spin-trap. Chronic experiments performed with Abca4^-/-Rdh8^-/- mice treated orally for 3 months with norbixin showed a reduced A2E accumulation in the retina. Norbixin appears promising for developing an oral treatment of macular degeneration. A drug candidate (BIO201) with 9’-cis-norbixin as the active principle ingredient is under development, and its potential will be assessed in a forthcoming clinical trial.

A novel fluorescence-based assay for measuring A2E removal from human retinal pigment epithelial cells to screen for age-related macular degeneration inhibitors

Age-related macular degeneration (AMD) is a common retinal disease that leads to irreversible central vision loss in the elderly population. Recent studies have identified many factors related to the development of dry AMD, such as aging, cigarette smoking, genetic predispositions, and oxidative stress, eventually inducing the accumulation of lipofuscin, which is one of the most critical risk factors. One of the major lipofuscins in retinal pigment epithelial (RPE) cells is N-retinylidene-N-retinylethanolamine (also known as A2E), a pyridinium bis-retinoid. Currently there is a lack of effective therapy to prevent or restore vision loss caused by dry AMD. Recent studies have shown that 430 nm blue light induces the oxidation of A2E and the activation of caspase-3 to subsequently cause the death of RPE cells, suggesting that removal of A2E from retinal pigment cells might be critical for preventing AMD. Here, we developed a fluorescence-labeled A2E analog (A2E-BDP) that functions similar to A2E in RPE cells, but is more sensitive to detection than A2E. A2E-BDP-based tracing of intracellular A2E will be helpful, not only for studying the accumulation and removal of A2E in human RPE cells but also for identifying possible inhibitors of AMD.

Retinoids and Retinal Diseases

Recent progress in molecular understanding of the retinoid cycle in mammalian retina stems from painstaking biochemical reconstitution studies supported by natural or engineered animal models with known genetic lesions and studies of humans with specific genetic blinding diseases. Structural and membrane biology have been used to detect critical retinal enzymes and proteins and their substrates and ligands, placing them in a cellular context. These studies have been supplemented by analytical chemistry methods that have identified small molecules by their spectral characteristics, often in conjunction with the evaluation of models of animal retinal disease. It is from this background that rational therapeutic interventions to correct genetic defects or environmental insults are identified. Thus, most presently accepted modulators of the retinoid cycle already have demonstrated promising results in animal models of retinal degeneration. These encouraging signs indicate that some human blinding diseases can be alleviated by pharmacological interventions.

Photodegradation of retinal bisretinoids in mouse models and implications for macular degeneration

Adducts of retinaldehyde (bisretinoids) form nonenzymatically in photoreceptor cells and accumulate in retinal pigment epithelial (RPE) cells as lipofuscin; these fluorophores are implicated in the pathogenesis of inherited and age-related macular degeneration (AMD). Here we demonstrate that bisretinoid photodegradation is ongoing in the eye. High-performance liquid chromatography (HPLC) analysis of eyes of dark-reared and cyclic light-reared wild-type mice, together with comparisons of pigmented versus albino mice, revealed a relationship between intraocular light and reduced levels of the bisretinoids A2E and A2-glycero-phosphoethanolamine (A2-GPE). Analysis of the bisretinoids A2E, A2-GPE, A2-dihydropyridine-phosphatidylethanolamine (A2-DHP-PE), and all-trans-retinal dimer-phosphatidylethanolamine (all-trans-retinal dimer-PE) also decreases in albino Abca4(-/-) mice reared in cyclic light compared with darkness. In albino Abca4(-/-) mice receiving a diet supplemented with the antioxidant vitamin E, higher levels of RPE bisretinoid were evidenced by HPLC analysis and quantitation of fundus autofluorescence; this effect is consistent with photooxidative processes known to precede bisretinoid degradation. Amelioration of outer nuclear layer thinning indicated that vitamin E treatment protected photoreceptor cells. Conversely, in-cage exposure to short-wavelength light resulted in reduced fundus autofluorescence, decreased HPLC-quantified A2E, outer nuclear layer thinning, and increased methylglyoxal (MG)-adducted protein. MG was also released upon bisretinoid photodegradation in cells. We suggest that the lower levels of these diretinal adducts in cyclic light-reared and albino mice reflect photodegradative loss of bisretinoid. These mechanisms may underlie associations among AMD risk, oxidative mechanisms, and lifetime light exposure.

Vitamin A-aldehyde adducts: AMD risk and targeted therapeutics

Although currently available treatment options for age-related macular degeneration (AMD) are limited, particularly for atrophic AMD, the identification of predisposing genetic variations has informed clinical studies addressing therapeutic options such as complement inhibitors and anti-inflammatory agents. To lower risk of early AMD, recommended lifestyle interventions such as the avoidance of smoking and the intake of low glycemic antioxidant-rich diets have largely followed from the identification of nongenetic modifiable factors. On the other hand, the challenge of understanding the complex relationship between aging and cumulative damage leading to AMD has fueled investigations of the visual cycle adducts that accumulate in retinal pigment epithelial (RPE) cells and are a hallmark of aging retina. These studies have revealed properties of these compounds that provide insights into processes that may compromise RPE and could contribute to disease mechanisms in AMD. This work has also led to the design of targeted therapeutics that are currently under investigation.

Predicting Progression of ABCA4-Associated Retinal Degenerations Based on Longitudinal Measurements of the Leading Disease Front

PURPOSE

To evaluate the progression of the earliest stage of disease in ABCA4-associated retinal degenerations (RDs).

METHODS

Near-infrared excited reduced-illuminance autofluorescence imaging was acquired across the retina up to 80 degrees eccentricity in 44 patients with two ABCA4 alleles. The eccentricity of the leading disease front (LDF) corresponding to the earliest stage of disease was measured along the four meridians. A mathematical model describing the expansion of the LDF was developed based on 6 years of longitudinal follow-up.

RESULTS

The extent of LDF along the superior, inferior, and temporal meridians showed a wide spectrum from 3.5 to 70 degrees. In patients with longitudinal data, the average centrifugal expansion rate was 2 degrees per year. The nasal extent of LDF between the fovea and ONH ranged from 4.3 to 16.5 degrees and expanded at 0.35 degrees per year. The extent of LDF beyond ONH ranged from 19 to 75 degrees and expanded on average at 2 degrees per year. A mathematical model fit well to the longitudinal data describing the expansion of the LDF.

CONCLUSIONS

The eccentricity of the LDF in ABCA4-RD shows a continuum from parafovea to far periphery along all four meridians consistent with a wide spectrum of severity observed clinically. The model of progression may provide a quantitative prediction of the LDF expansion based on the age and eccentricity of the LDF at a baseline visit, and thus contribute significantly to the enrollment of candidates appropriate for clinical trials planning specific interventions, efficacy outcomes, and durations.

Protective effect of autophagy on human retinal pigment epithelial cells against lipofuscin fluorophore A2E: implications for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly. Degeneration of retinal pigment epithelial (RPE) cells is a crucial causative factor responsible for the onset and progression of AMD. A2E, a major component of toxic lipofuscin implicated in AMD, is deposited in RPE cells with age. However, the mechanism whereby A2E may contribute to the pathogenesis of AMD remains unclear. We demonstrated that A2E was a danger signal of RPE cells, which induced autophagy and decreased cell viability in a concentration- and time-dependent manner. Within 15 min after the treatment of RPE with 25 μM A2E, the induction of autophagosome was detected by transmission electron microscopy. After continuous incubating RPE cells with A2E, intense punctate staining of LC3 and increased expression of LC3-II and Beclin-1 were identified. Meanwhile, the levels of intercellular adhesion molecule (ICAM), interleukin (IL)1β, IL2, IL-6, IL-8, IL-17A, IL-22, macrophage cationic peptide (MCP)-1, stromal cell-derived factor (SDF)-1, and vascular endothelial growth factor A (VEGFA) were elevated. The autophagic inhibitor 3-methyladenine (3-MA) and activator rapamycin were also used to verify the effect of autophagy on RPE cells against A2E. Our results revealed that 3-MA decreased the autophagosomes and LC3 puncta induced by A2E, increased inflammation-associated protein expression including ICAM, IL1β, IL2, IL-6, IL-8, IL-17A, IL-22, and SDF-1, and upregulated VEGFA expression. Whereas rapamycin augmented the A2E-mediated autophagy, attenuated protein expression of inflammation-associated and angiogenic factors, and blocked the Akt/mTOR pathway. Taken together, A2E induces autophagy in RPE cells at the early stage of incubation, and this autophagic response can be inhibited by 3-MA or augmented by rapamycin via the mTOR pathway. The enhancement of autophagy has a protective role in RPE cells against the adverse effects of A2E by reducing the secretion of inflammatory cytokines and VEGFA.

The genetics of age-related macular degeneration (AMD)--Novel targets for designing treatment options?

Age-related macular degeneration (AMD) is a progressive disease of the central retina and the main cause of legal blindness in industrialized countries. Risk to develop the disease is conferred by both individual as well as genetic factors with the latter being increasingly deciphered over the last decade. Therapeutically, striking advances have been made for the treatment of the neovascular form of late stage AMD while for the late stage atrophic form of the disease, which accounts for almost half of the visually impaired, there is currently no effective therapy on the market. This review highlights our current knowledge on the genetic architecture of early and late stage AMD and explores its potential for the discovery of novel, target-guided treatment options. We reflect on current clinical and experimental therapies for all forms of AMD and specifically note a persisting lack of efficacy for treatment in atrophic AMD. We further explore the current insight in AMD-associated genes and pathways and critically question whether this knowledge is suited to design novel treatment options. Specifically, we point out that known genetic factors associated with AMD govern the risk to develop disease and thus may not play a role in its severity or progression. Treatments based on such knowledge appear appropriate rather for prevention than treatment of manifest disease. As a consequence, future research in AMD needs to be greatly focused on approaches relevant to the patients and their medical needs.

Topical cyclodextrin reduces amyloid beta and inflammation improving retinal function in ageing mice

Retinal ageing results in chronic inflammation, extracellular deposition, including that of amyloid beta (Aβ) and declining visual function. In humans this can progress into age-related macular degeneration (AMD), which is without cure. Therapeutic approaches have focused on systemic immunotherapies without clinical resolution. Here, we show using aged mice that 2-Hydroxypropyl-β-cyclodextrin, a sugar molecule given as eye drops over 3 months results in significant reductions in Aβ by 65% and inflammation by 75% in the aged mouse retina. It also elevates retinal pigment epithelium specific protein 65 (RPE65), a key molecule in the visual cycle, in aged retina. These changes are accompanied by a significant improvement in retinal function measured physiologically. 2-Hydroxypropyl-β-cyclodextrin is as effective in reducing Aβ and inflammation in the complement factor H knockout (Cfh(-/-)) mouse that shows advanced ageing and has been proposed as an AMD model. β-cyclodextrin is economic, safe and may provide an efficient route to reducing the impact of retinal ageing.

Morphological and physiological retinal degeneration induced by intravenous delivery of vitamin A dimers in rabbits

The eye uses vitamin A as a cofactor to sense light and, during this process, some vitamin A molecules dimerize, forming vitamin A dimers. A striking chemical signature of retinas undergoing degeneration in major eye diseases such as age-related macular degeneration (AMD) and Stargardt disease is the accumulation of these dimers in the retinal pigment epithelium (RPE) and Bruch's membrane (BM). However, it is not known whether dimers of vitamin A are secondary symptoms or primary insults that drive degeneration. Here, we present a chromatography-free method to prepare gram quantities of the vitamin A dimer, A2E, and show that intravenous administration of A2E to the rabbit results in retinal degeneration. A2E-damaged photoreceptors and RPE cells triggered inflammation, induced remolding of the choroidal vasculature and triggered a decline in the retina's response to light. Data suggest that vitamin A dimers are not bystanders, but can be primary drivers of retinal degeneration. Thus, preventing dimer formation could be a preemptive strategy to address serious forms of blindness.

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.

Quantitative autofluorescence and cell density maps of the human retinal pigment epithelium

PURPOSE

Lipofuscin (LF) accumulation within RPE cells is considered pathogenic in AMD. To test whether LF contributes to RPE cell loss in aging and to provide a cellular basis for fundus autofluorescence (AF) we created maps of human RPE cell number and histologic AF.

METHODS

Retinal pigment epithelium-Bruch's membrane flat mounts were prepared from 20 donor eyes (10 ≤ 51 and 10 > 80 years; postmortem: ≤4.2 hours; no retinal pathologies), preserving foveal position. Phalloidin-binding RPE cytoskeleton and LF-AF (488-nm excitation) were imaged at up to 90 predefined positions. Maps were assembled from 83,330 cells in 1470 locations. From Voronoi regions representing each cell, the number of neighbors, cell area, and total AF intensity normalized to an AF standard was determined.

RESULTS

Highly variable between individuals, RPE-AF increases significantly with age. A perifoveal ring of high AF mirrors rod photoreceptor topography and fundus-AF. Retinal pigment epithelium cell density peaks at the fovea, independent of age, yet no net RPE cell loss is detectable. The RPE monolayer undergoes considerable lifelong re-modeling. The relationship of cell size and AF, a surrogate for LF concentration, is orderly and linear in both groups. Autofluorescence topography differs distinctly from the topography of age-related rod loss.

CONCLUSIONS

Digital maps of quantitative AF, cell density, and packing geometry provide metrics for cellular-resolution clinical imaging and model systems. The uncoupling of RPE LF content, cell number, and photoreceptor topography in aging challenges LF's role in AMD.