Medical treatment of cataract

Stereolithographic Rapid Prototyping of Clear, Foldable, Non-Refractive Intraocular Lens Designs: A Proof-of-Concept Study

PURPOSE

A cataract is a cloudy area in the crystalline lens. Cataracts are the leading cause of blindness and the second cause of severe vision impairment worldwide. During cataract surgery, the clouded lens is extracted and replaced with an artificial intraocular lens, which restores the optical power. The fabrication of intraocular lenses using existing molding and lathing techniques is a complex and time-consuming process that limits the development of novel materials and designs. To overcome these limitations, we have developed a stereolithography-based process for producing models of clear lens designs without refractive function, serving as a proof of concept. This process has the potential to contribute toward new lens development, allowing for unlimited design iterations and an expanded range of materials for scientists to explore.

METHODS

Lens-like 3D objects without refractive function were fabricated by using stereolithography. A photopolymerizable resin containing 2-phenoxyethyl acrylate, poly (ethylene glycol) dimethacrylate, and a suitable photoinitiator was developed for the production of lens-like 3D object prototypes. The morphology of the printed devices was characterized by scanning electron microscopy. The transparency and thermal properties were analyzed using spectrophotometry and differential scanning calorimetry, respectively. The biocompatibility of the devices was investigated in a cultured human lens cell line (FHL-124), using a standard lactate dehydrogenase assay, and the lenses were folded and implanted in the human capsular bag model.

RESULTS

One-piece lens-like 3D objects without refractive function and with loop-haptic design were successfully fabricated using Stereolithography (SLA) technique. The resulting 3D objects were transparent, as determined by UV spectroscopy. The lactate dehydrogenase test demonstrated the tolerance of lens cells to the prototyping material, and apparent foldability and shape recovery was observed during direct injection into a human capsular bag model in vitro.

CONCLUSIONS

This proof-of-principle study demonstrated the potential and significance of the rapid prototyping process for research and development of lens-like 3D object prototypes, such as intraocular lenses.

Effects of Laurus Nobilis Eye Drop on Selenite-Induced Cataract Formation and Oxidative Stress-Related Parameters in Rabbits: An Experimental Study

PURPOSE

To evaluate the protective role of Laurus Nobilis eye drops on selenite-induced cataracts in suckling rabbits.

METHODS

Fifteen male albino suckling rabbits with no signs of ocular inflammation were randomly assigned to three groups: controls (Group A), sodium-selenite group (Group B) and sodium-selenite plus Laurus Nobilis group (Group C). By selenite treatment, cataract formation was experimentally induced and then graded. The grade of oxidative stress was defined in the lens, measuring the concentration of malondialdehyde, alpha-tocopherol, oxidized glutathione, ascorbic acid and hydrogen peroxide, and in blood samples as levels of alpha-tocopherol and malondialdehyde.

RESULTS

Mean lens concentrations of GSSG, H2O2, and MDA levels in group B were significantly higher than in both group C and control. Ascorbic acid and alpha-tocopherol concentrations were lower in group B than in both group C and A. As plasma oxidative status markers, the level of MDA was higher in group B respected group C and A. The mean alpha-tocopherol levels in group B were significantly lower than in both group A and group C.

CONCLUSIONS

In animals treated with Laurus Nobilis-based eye drops, inflammation was inhibited, and lipid peroxidation was significantly reduced. Laurus nobilis leaves extract represents a good source of antioxidant components that may contrast sodium selenite-induced cataractogenesis in suckling rabbits.

Natural aldose reductase inhibitors for treatment and prevention of diabetic cataract: A review

Introduction: Aldose reductase (AR) is an enzyme that catalyzes the reduction of glucose to sorbitol responsible for the development of diabetic complications like cataracts. Medicinal plants contain several phytocompounds that can inhibit this enzyme.

Objective: The purpose of this review is to cite medicinal plants that have been tested for their ability to inhibit aldose reductase and consequently prevent cataracts and classify the major isolated compounds that have this activity.

Methods: We reviewed 154 articles published between 1954 and 2020 in English via three databases: ScienceDirect, Web of Science, and PubMed. We have classified the plants that showed a significant anti-cataract effect, in the form of a list including the scientific and family names of each plant. Also, we have cited the IC50 values and the active constituents of each plant that showed inhibitory activity towards AR.

Results: We have described 38 herbs belonging to 29 families. Besides, 47 isolated compounds obtained from the cited herbs have shown an AR inhibitory effect: luteolin, luteolin-7-O-β-D-glucopyranoside, apigenin, 3,5-di-O-caffeoyl-epi-quinic acid, delphinidin 3-O-β-galactopyranoside-3’-O-β-glucopyranoside, 3,5-di-O-caffeoylquinic acid methyl ester, andrographolide, 1,2,3,6-tetra-O-galloyl-β-D-glucose, 1,2,4,6-tetra-O-galloyl-β-D-glucose, 7-(3-hydroxypropyl)-3-methyl-8-β-O-D-glucoside-2H-chromen-2-one, E-4-(60-hydroxyhex-30-en-1-yl)phenyl propionate, delphinidin 3-O-β-galactopyranoside-3’,5’-di-O-β-glucopyranoside, 1,2,3-tri-O-galloyl-β-D-glucose, 1,2,3,4,6-penta-O-galloyl-β-D-glucose, 1,2,6-tri-O-galloyl-β-D-glucose, 2-(4-hydroxy-3-methoxyphenyl)ethanol, (4-hydroxy-3-methoxyphenyl)methanol, trans-anethole, gallic acid 4-O-β-D-(6’-O-galloyl)-glucoside, β-glucogallin, puerariafuran, quercetin, gallic acid 4-O-β-D-glucoside, 2,5-dihydroxybenzoic acid, 4-(4-hydroxy-3-methoxyphenyl)-2-butanone, protocatechuic acid, trans-cinnamic acid, gallic acid, p-coumaric acid and syringic acid.

Conclusion: natural therapy becomes an interesting alternative in the treatment and prevention of cataract by using medicinal plants rich in active compounds considered as AR inhibitors.

Yeast-produced fructosamine-3-kinase retains mobility after ex vivo intravitreal injection in human and bovine eyes as determined by Fluorescence Correlation Spectroscopy

Globally, over 2 billion people suffer from vision impairment. Despite complex multifactorial etiology, advanced glycation end products are involved in the pathogenesis of many causative age- and diabetes-related eye diseases. Deglycating enzyme fructosamine-3-kinase (FN3K) was recently proposed as a potential therapeutic, but for further biopharmaceutical development, knowledge on its manufacturability and stability and mobility in the vitreous fluid of the eye is indispensable. We evaluated recombinant production of FN3K in two host systems, and its diffusion behavior in both bovine and human vitreous. Compared to Escherichia coli, intracellular production in Pichia pastoris yielded more and higher purity FN3K. The yeast-produced enzyme was used in a first attempt to use fluorescence correlation spectroscopy to study protein mobility in non-sonicated bovine vitreous, human vitreous, and intact bovine eyes. It was demonstrated that FN3K retained mobility upon intravitreal injection, although a certain delay in diffusion was observed. Alkylation of free cysteines was tolerated both in terms of enzymatic activity and vitreous diffusion. Ex vivo diffusion data gathered and the availability of yeast-produced high purity enzyme now clear the path for in vivo pharmacokinetics studies of FN3K.

Amphiphilic silicones to mitigate lens epithelial cell growth on intraocular lenses

Silicone intraocular lenses (IOLs) that resist lens epithelial cell (LEC) growth would greatly improve patient outcomes. Herein, amphiphilic surface modifying additives (SMAs) were incorporated into an IOL-type diphenyl silicone to reduce LEC growth without compromising opto-mechanical properties. The SMAs were poly(ethylene oxide)-silane amphiphiles (PEO-SAs) [H-Si-ODMS_m-block-PEO₈-OCH₃], comprised of a PEO segment and siloxane tether of varying lengths (m = 0, 13, and 30). These three SMAs were each blended into the addition cure diphenyl silicone at varying concentrations (5, 10, 15, 20, and 25 μmol g^-1) wherein the wt% of PEO was maintained for all SMAs at a given molar concentration. The chemical crosslinking and subsequent retention of SMAs in modified silicones was confirmed. Key material properties were assessed following equilibration in both air and aqueous environments. Silicones modified with SMAs having longer tethers (m = 13 and 30) underwent rapid and substantial water-driven restructuring of PEO to the surface to form highly hydrophilic surfaces, especially as SMA concentration increased. The % transmittance was also maintained for silicones modified with these particular SMAs. The moduli of the modified silicones were largely unchanged by the SMA and remained in the typical range for silicone IOLs. When the three SMAs were introduced at the highest concentration, modified silicones remained non-cytotoxic and LEC count and associated alpha-smooth muscle actin (α-SMA) expression decreased with increasing tether length. These results demonstrate the potential of silicones modified with PEO-SA SMAs to produce LEC-resistant IOLs.

Effect of oral antioxidants on the progression of canine senile cataracts: a retrospective study

Background

Cataracts are the leading cause of impaired vision or blindness in dogs. There are many antioxidants that can prevent cataract progression, but whether they are clinically effective in dogs has not been established.

Objectives

To analyze the delaying or preventing effect of oral antioxidants on canine senile cataracts through retrospective analysis.

Methods

Medical records of dogs from January 1, 2015 to July 10, 2020 were reviewed. Dogs that were 8 yr of age or older with senile cataracts were included in this study. The dogs were divided into two treatment groups (dogs administered with Ocu-GLO supplement and dogs administered with Meni-One Eye R/C supplement) and a control group (dogs that were not administered any supplement). Dogs with incipient and immature cataracts were included in this study. Altogether, 112 dogs (156 eyes) with incipient cataracts and 60 dogs (77 eyes) with immature cataracts were included. The period of time that cataracts progressed from incipient to immature, and from immature to mature was recorded for each dog.

Results

There was no significant delaying effect on the progression of incipient cataracts. However, both Ocu-GLO (hazard ratio = 0.265, p = 0.026) and Meni-One (hazard ratio = 0.246, p = 0.005) significantly delayed the progression of immature cataracts compared to the control group.

Conclusions

Although there was no significant delaying effect of oral antioxidants on incipient cataract progression, antioxidants could be used to delay the progression of senile immature cataract.

Nanoceria Prevents Glucose-Induced Protein Glycation in Eye Lens Cells

Cerium oxide nanoparticles (nanoceria) are generally known for their recyclable antioxidative properties making them an appealing biomaterial for protecting against physiological and pathological age-related changes that are caused by reactive oxygen species (ROS). Cataract is one such pathology that has been associated with oxidation and glycation of the lens proteins (crystallins) leading to aggregation and opacification. A novel coated nanoceria formulation has been previously shown to enter the human lens epithelial cells (HLECs) and protect them from oxidative stress induced by hydrogen peroxide (H2O2). In this work, the mechanism of nanoceria uptake in HLECs is studied and multiple anti-cataractogenic properties are assessed in vitro. Our results show that the nanoceria provide multiple beneficial actions to delay cataract progression by (1) acting as a catalase mimetic in cells with inhibited catalase, (2) improving reduced to oxidised glutathione ratio (GSH/GSSG) in HLECs, and (3) inhibiting the non-enzymatic glucose-induced glycation of the chaperone lens protein α-crystallin. Given the multifactorial nature of cataract progression, the varied actions of nanoceria render them promising candidates for potential non-surgical therapeutic treatment.

Preloaded vs manually loaded IOL delivery systems in cataract surgery in the largest ambulatory surgery center of northwestern China: an efficiency analysis

BACKGROUND

To compare the efficiency of preloaded vs manually loaded IOL (P-IOL vs M-IOL, respectively) delivery systems in cataract surgery in the largest ambulatory surgery center of Northwestern China.

METHODS

A total of 200 cases were included in this prospective, observational study. Time and motion data were collected in a one- or two-operating room (1-OR or 2-OR, respectively) scenario. A model of the efficiency and revenue implications of introducing a preloaded delivery system for IOLs in cataract surgery was used to estimate the changes in cataract throughput and hospital revenue through transitioning from the M-IOL delivery system to the P-IOL system.

RESULTS

In the 1-OR scenario, the mean total case time was 16.9 min using P-IOL, which was a 7.7% reduction compared with M-IOL (P < 0.01). In the 2-OR scenario, the mean total surgeon time was 10.8 min using P-IOL, which was a 7.8% reduction compared with M-IOL (P < 0.05). By switching from M-IOL to P-IOL, annual throughput will increase by 5.2% (960 cases) in the 1-OR scenario and 7.7% (1440 cases) in the 2-OR scenario, accompany by an increase in revenue of approx. 284,352 USD in the 1-OR scenario and approx. 426,528 USD in the 2-OR scenario.

CONCLUSION

This report is the first of a comparison of two IOL delivery systems in China using different settings in the scenario. IOL delivery with preloaded systems is time saving in both the 1-OR scenario and the 2-OR scenario. Moreover, switching from the M-IOL delivery system to the P-IOL system holds potential to increase cataract throughput and hospital revenue.

Visual and subjective outcomes following trifocal intraocular lens implantation in Iranian cataractous patients

BACKGROUND

The aim of this study was to evaluate visual and refractive outcomes and quality of vision after implantation of the AT LISA tri 839MP intraocular lens (IOL).

PATIENTS AND METHODS

This interventional clinical trial comprised 46 cataractous eyes of patients who underwent phacoemulsification with IOL implantation (mean age of 58.08 ± 11.01 years; range: 36-76 years old). Spherical equivalent (SE), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), uncorrected intermediate visual acuity (UIVA), corrected intermediate visual acuity (CIVA), uncorrected near visual acuity (UNVA), and corrected near visual acuity (CNVA) were measured 1, 3, and 6 months after surgery. Contrast sensitivity (CS) was measured at 6 months. Subjective quality of vision and presence of dysphotopsia by a short questionnaire were evaluated postoperatively.

RESULTS

At 6 months, the mean visual acuity was 0.08 ± 0.11, 0.03 ± 0.08, 0.07 ± 0.09, 0.02 ± 0.08, 0.05 ± 0.09, and 0.02 ± 0.08 LogMAR for UDVA, CDVA, UIVA, CIVA, UNVA, and CNVA, respectively. The mean values of SE were - 0.4728 ± 0.32D. These variables improved over time, yet significant changes were detected in UDVA (P = 0.009) and SE (P = 0.0001). The mean CS value was 1.74 ± 0.08. The mean scores (0% = no symptoms; 100% = strong symptoms/unable to perform activities) for glare and halos were 7.07 ± 0.22% and 8.70 ± 0.23%, respectively. These items were reduced over time. Patients' level of satisfaction mean score for performing activities was 96.66%.

CONCLUSIONS

The AT LISA tri 839MP IOL provides excellent uncorrected distance, intermediate and near vision, and CS. This IOL showed a minimal level of photic phenomena and a high level of patient satisfaction.

Biology of Inherited Cataracts and Opportunities for Treatment

Cataract, the clinical correlate of opacity or light scattering in the eye lens, is usually caused by the presence of high-molecular-weight (HMW) protein aggregates or disruption of the lens microarchitecture. In general, genes involved in inherited cataracts reflect important processes and pathways in the lens including lens crystallins, connexins, growth factors, membrane proteins, intermediate filament proteins, and chaperones. Usually, mutations causing severe damage to proteins cause congenital cataracts, while milder variants increasing susceptibility to environmental insults are associated with age-related cataracts. These may have different pathogenic mechanisms: Congenital cataracts induce the unfolded protein response and apoptosis. By contrast, denatured crystallins in age-related cataracts are bound by α-crystallin and form light-scattering HMW aggregates. New therapeutic approaches to age-related cataracts use chemical chaperones to solubilize HMW aggregates, while attempts are being made to regenerate lenses using endogenous stem cells to treat congenital cataracts.

Medicinal Plants and Natural Products Used in Cataract Management

Cataract is the leading reason of blindness worldwide and is defined by the presence of any lens opacities or loss of transparency. The most common symptoms of cataract are impaired vision, decreased contrast sensitivity, color disturbance, and glare. Oxidative stress is among the main mechanisms involved in the development of age-related cataract. Surgery through phacoemulsification and intraocular lens implantation is the most effective method for cataract treatment, however, there are chances of serious complications and irreversible loss of vision associated with the surgery. Natural compounds consisting of antioxidant or anti-inflammatory secondary metabolites can serve as potential leads for anticataract agents. In this review, we tried to document medicinal plants and plant-based natural products used for cataract treatment worldwide, which are gathered from available ethnopharmacological/ethnobotanical data. We have extensively explored a number of recognized databases like Scifinder, PubMed, Science Direct, Google Scholar, and Scopus by using keywords and phrases such as “cataract”, “blindness”, “traditional medicine”, “ethnopharmacology”, “ethnobotany”, “herbs”, “medicinal plants”, or other relevant terms, and summarized the plants/phytoconstituents that are evaluated in different models of cataract and also tabulated 44 plants that are traditionally used in cataract in various folklore medical practices. Moreover, we also categorized the plants according to scientific studies carried out in different cataract models with their mechanisms of action.

Dietary antioxidant for disease prevention corroborated by the Nrf2 pathway

Dietary antioxidants are widely distributed in various types of our food. They are strongly associated with reduced risk of many chronic diseases such as atherosclerosis, cancer, and Alzheimer's diseases. They include vitamins such as vitamins A, E, C, and carotenoids. Also, some minerals like; zinc, manganese, copper, iron, and selenium are essential for the activity of antioxidant enzymes. Furthermore, dietary polyphenols and flavonoids are considered as potent antioxidant compounds. Vegetables, fruits, and edible herbs are the richest sources of such antioxidants. Antioxidants reduce oxidative stress, either directly by reducing reactive species or indirectly by enhancing the body antioxidant defense mechanisms in different ways. These may include upregulating gene expression of some antioxidant enzymes via a nuclear factor erythroid 2 related factor2 pathway. Administration of a mixture of antioxidants is beneficial since they act synergistically in various phases. The aims of this review are to summarize the different antioxidants from dietary sources and their role in the prevention of different diseases.

Mutations and mechanisms in congenital and age-related cataracts

The crystalline lens plays an important role in the refractive vision of vertebrates by facilitating variable fine focusing of light onto the retina. Loss of lens transparency, or cataract, is a frequently acquired cause of visual impairment in adults and may also present during childhood. Genetic studies have identified mutations in over 30 causative genes for congenital or other early-onset forms of cataract as well as several gene variants associated with age-related cataract. However, the pathogenic mechanisms resulting from genetic determinants of cataract are only just beginning to be understood. Here, we briefly summarize current concepts pointing to differences in the molecular mechanisms underlying congenital and age-related forms of cataract.

Anticataractogenesis Mechanisms of Curcumin and a Comparison of Its Degradation Products: An in Vitro Study

Curcumin (Cur) exhibits anticataractogenesis activity. This study aimed to compare the activities of Cur with those of its degradation products in a series of in vitro lens protein turbidity assays. The results show that Cur (200 μM) ameliorates selenite-induced crystallin aggregation, and the mean OD value was 0.10 ± 0.02 (p < 0.05), which was significantly different from controls (0.15 ± 0.01) after incubating for 3 days. However, Cur did not significantly inhibit calcium-induced proteolysis after incubating for 3 days. Such results were supported by isothermal titration calorimetry observation that Cur binds with selenite but not with calcium. Presence of Cur and the degradation products examined (ferulic acid, cinnamic acid, vanillin, and vanillic acid) indicates significantly protective activities on lens γ-crystallins after UVC exposure for 3 h. Among the compounds examined, only ferulic acid exhibited a significant inhibitory effect against UVB-induced turbidity with a mean OD of 0.32 ± 0.01 (p < 0.05), which was significantly different from controls (0.49 ± 0.02). The previously reported anticataract effects of Cur may stem not only from Cur but also from its degradation products through various cataractogenesis mechanisms in vitro.

Carnosine and Related Peptides: Therapeutic Potential in Age-Related Disorders

Imidazole dipeptides (ID), such as carnosine (β-alanyl-L-histidine), are compounds widely distributed in excitable tissues of vertebrates. ID are also endowed of several biochemical properties in biological tissues, including antioxidant, bivalent metal ion chelating, proton buffering, and carbonyl scavenger activities. Furthermore, remarkable biological effects have been assigned to such compounds in age-related human disorders and in patients whose activity of serum carnosinase is deficient or undetectable. Nevertheless, the precise biological role of ID is still to be unraveled. In the present review we shall discuss some evidences from clinical and basic studies for the utilization of ID as a drug therapy for age-related human disorders.

Ocular delivery of cyanidin-3-glycoside in liposomes and its prevention of selenite-induced oxidative stress

CONTEXT

Cataracts have become the leading cause of blindness around the world, which is mainly mediated by oxidative stress.

OBJECTIVE

N-trimethyl chitosan (TMC)-coated liposomes of cyanidin-3-glycoside (C3G) (C3G-TCL) were prepared to attenuate oxidative stress induced by selenite sodium in rats.

MATERIALS AND METHODS

C3G-TCL were prepared by reverse-phase evaporation method and then coated with self-synthesized TMC. The physicochemical properties were determined. A gamma-scintigraphy study was employed to evaluate the precorneal elimination of the radioactive preparations. The transcorneal visualization for fluorescence-labeled samples was determined by confocal laser scanning microscopy (CLSM). The in vivo anti-oxidative study using C3G-TCL was carried out in rats with selenite-induced cataracts by topical administration.

RESULTS

The sphere-like morphological characterization of the vesicles was confirmed by TEM, with a size of 158.3 ± 2.8 nm and a zeta potential of 31.7 mV. The encapsulation efficiency was (53.7 ± 0.2) % as measured by ultrafiltration. C3G-TCL showed a 3.3-fold increment in precorneal residence time when compared with that of the (99m)Tc-solution. A TMC coating enhanced the transepithelial transport of liposomes to a depth of 40-μm in the cornea. Moreover, C3G-TCL could significantly elevate the activity of superoxide dismutase and catalase in lens and also show a considerable reversal of reduced glutathione activity. The lipid peroxidation in lens was strongly prevented when compared with that of groups treated with uncoated C3G-loaded liposomes.

DISCUSSION AND CONCLUSION

The coating material TMC for liposomes helps improve the anti-oxidative effect of C3G in vivo through prolonged residence time on the cornea and improved permeability in the corneal epithelium.

Analytical and physicochemical characterisation of the senile cataract drug dipeptide β-alanyl-L-histidine (carnosine)

This study presents a simple but sensitive HPLC chromatographic method with a stability-indicating assay for determination and physicochemical characterisation of L-carnosine, a promising senile cataract prophylactic agent. Chromatographic analysis was conducted using a reverse phase (RP)-HPLC system and an isocratic mobile phase of 98% v/v trifluoroacetic acid (0.1% v/v) and 2% v/v acetonitrile with detection at 220 nm. L-carnosine was subjected to stress conditions to force its degradation using chemical and thermal agents and was subsequently detected from its degradation products using ESI-MS. The lipophilicity of the drug and 1:1 drug to phospholipid complex (PC) mol/mol was determined by estimating the partition coefficient (P). Lipophilicity was greatly enhanced when L-carnosine was formulated as a phospholipid complex using the solvent evaporation method. L-carnosine-phospholipid complex could be a promising approach for effective delivery to the human lens as offers a potential novel treatment for senile cataract.

Use of cataract surgery in urban Beijing: a post screening follow-up of the elderly with visual impairment due to age-related cataract

OBJECTIVE

To understand the perception for the use of cataract surgical services in a population of acceptors and non-acceptors of cataract surgery in urban Beijing.

METHODS

From a community-based screening program a total of 158 patients with presenting visual acuity of less than 6/18 on either eye due to age-related cataract were informed about the possibility of surgical treatment. These patients were interviewed and re-examined 36 to 46 months after initial screening. The main reasons for not accepting surgery were obtained using a questionnaire. Vision function and vision-related quality of life scores were assessed in those who received and did not receive surgery.

RESULTS

At the follow-up examination 116 of the 158 patients were available and 36 (31.0%) had undergone cataract surgery. Cases who chose surgery had higher education level than those who did not seek surgery (OR=2.64, 95% CI: 1.08-6.63, P=0.02). There were no significant differences in vision function (P=0.11) or quality of life scores (P=0.16) between the surgery group and the non-surgery group. Main reasons for not having surgery included no perceived need (50.0%), feeling of being "too old" (19.2%), and worry about the quality of surgery (9.6%). Cost was cited by 1 (1.9%) subject as the main reason for not seeking surgery.

CONCLUSIONS

The data suggest that in China's capital urban center for patients with moderate visual impairment there is a relative low acceptance rate of cataract surgery, mainly due to people's perception of marginal benefits of surgery. Cost is not a determining factor as barrier to undergo surgery and patients with poorer education are less likely to undertake surgery.

Age-related cataract and drug therapy: opportunities and challenges for topical antioxidant delivery to the lens

Objectives

The search for anticataract drugs has been continuing for decades; some treatments no longer exist but antioxidants are still of much interest.

Key findings

The primary function of the human lens, along with the cornea, is to refract light so that it is correctly focused onto the retina for optimum image quality. With age, the human lens undergoes morphological, biochemical and physical changes leading to opacification. Age-related or senile cataract is one of the main causes of visual impairment in the elderly; given the lack of access to surgical treatment in many parts of the world, cataract remains a major cause of sight loss. Surgical treatment is the only means of treating cataract; this approach, however, has limitations and complications.

Summary

This review discusses the anatomy and physiology of the lens and the changes that are understood to occur with ageing and cataract formation to identify potential areas for effective therapeutic intervention. Experimental techniques and agents used to induce cataract in animal models, the advantages and disadvantages of potential pharmacological treatments specific barriers to delivery of exogenous antioxidants to the lens and the prospects for future research are discussed.

Antioxidants and vision health: facts and fiction

A number of nutritional supplements containing antioxidants are advertised for better vision health. Do they benefit the average consumer? The literature was examined for the effectiveness of antioxidants for human eye health, and for the intricacies in collection of such evidence. The following diseases were considered: cataract, glaucoma, age-related macular degeneration (AMD), retinopathy, retinitis pigmentosa, eye infections, and uveitis. The literature indicates that antioxidant supplements plus lutein have a reasonable probability of retarding AMD. For glaucoma, such supplements were ineffectual in some studies but useful in others. In some studies, antioxidant rich fruits and vegetables were also useful for protection against glaucoma. For diabetic retinopathy, antioxidant supplements may have a small benefit, if any, but only as an adjunct to glycemic control. In very high-risk premature retinopathy and retinitis pigmentosa, antioxidant supplements may be beneficial but those with excess Vitamin E should be avoided. For cataract, there is no evidence for an advantage of such nutritional supplements. However, lubricant drops containing N-acetylcarnosine may be helpful in initial stages of the disease. For eye infections and other causes of uveitis, antioxidants have not been found useful. We recommend that a diet high in antioxidant rich foods should be developed as a habit from an early age. However, when initial signs of vision health deterioration are observed, the appropriate nutritional supplement products may be recommended but only to augment the primary medical treatments.

Rutin ameliorates free radical mediated cataract by enhancing the chaperone activity of α-crystallin

BACKGROUND

Cataract, the leading cause of blindness, is associated with oxidative damage and protein modification in the lens. The present study was carried out to assess the efficacy of rutin on rat-lens crystallins in selenite-induced in-vivo cataract models.

METHODS

Eight-day-old Sprague-Dawley rat pups were grouped as control (G I), experimental (G II) and rutin-treated (G III). The rat pups in G II, and G III received a single subcutaneous injection of sodium selenite (4 μg/g body weight) and G I received a single subcutaneous injection of sterile water on the 10th day. The treatment groups (G III) were administered with rutin (1 μg/g body weight) respectively from the 8th to 15th day. Cataract was visualized from the 16th day. Lens crystallins (α, β, and γ) were isolated by size exclusion chromatography. Chaperone activity of isolated crystallins was measured by heat, DTT, and oxidation-induced aggregation and refolding assays. Concentration of total protein (soluble and insoluble) and SDS-PAGE analysis of soluble proteins were also done.

RESULTS

Treatment with rutin prevented the loss of α crystallin chaperone property, and protein insolubilization prevailed during selenite-induced cataract.

CONCLUSIONS

These results suggest the therapeutic potential of rutin, a bioflavonoid, against selenite-induced cataract, which has been reported in this paper for the first time. The work assumes significance, as this is a novel approach in modulating the chaperone activity of lens crystallins in selenite-induced cataract by a natural product.

The Impact of Senile Cataract Maturity on Blood Oxidative Stress Markers and Glutathione-Dependent Antioxidants: Relations with Lens Variables

Oxidative stress is implicated in senile cataract (SC) genesis, although the impact of SC maturity on blood oxidative stress markers is unclear. Total hydroperoxides, malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) were measured in the blood and lens samples of patients having either immature (n=31) or mature SC (n=50), and in 22 blood samples from noncataract controls. Compared to controls, SC patients had higher plasma MDA and serum GST, and decreased plasma GR and GSH levels. Plasma GPx as well as hydroperoxides differed from control values only in patients with mature SC. The multivariate logistic regression analysis showed that the fall of plasma GR activity (OR 5.14; CI 1.82-14.51;p=0.0020), as well as serum GST activity (OR 3.84; CI 1.36-10.83;p=0.0108) were independently associated with the maturity of SC. Lens hydroperoxides, MDA and GST, showed no correlation with correspondent blood values, in contrast to GPx (r=0.715; p<0.001) and GR (r=0.703; p<0.001). This study showed that the severity of SC is associated with increased systemic oxidative stress, which could be due to the fall of GSH-dependent antioxidant enzymes activities.

Prevention of selenite-induced cataractogenesis by an ethanolic extract of Cineraria maritima: an experimental evaluation of the traditional eye medication

In the present study, the antioxidant potential of an ethanolic extract of Cineraria maritima and its efficacy in preventing selenite-induced cataractogenesis were assessed in vitro and in vivo. In the in vitro phase of the study, lenses dissected out from the eyes of Wistar rats were incubated for 24 h at 37 °C in Dulbecco's modified Eagle medium (DMEM) alone (group I), in DMEM containing 100 μM of selenite only (group II), or in DMEM containing 100 μM of selenite and 300 μg/ml C. maritima extract added at the same time (group III). Gross morphological examination of the lenses revealed dense opacification in group II, minimal opacification in group III, and no opacification in group I lenses. The mean activities of the antioxidant enzymes catalase, glutathione peroxidase, and superoxide dismutase were significantly lower in group II than in group I or group III lenses, while malondialdehyde concentration was significantly higher in group II lenses than in group I and group III lenses. In the in vivo phase of the study, dense opacification of lenses was noted in all rat pups (100%) that had received a single subcutaneous injection of sodium selenite alone (19 μM/kg body weight) on postpartum day 10, whereas cataract formation occurred in only 33.3% of rat pups that had received selenite as well as an intraperitoneal injection of the extract of C. maritima (350 mg/kg body weight) for five consecutive days. These observations suggest that the ethanolic extract of C. maritima may prevent experimental selenite-induced cataractogenesis.

Contribution of cholesterol and oxysterols in the physiopathology of cataract: implication for the development of pharmacological treatments

The development of cataract is associated with some lipid changes in human lens fibers, especially with increased accumulation and redistribution of cholesterol inside these cells. Some direct and indirect lines of evidence, also suggest an involvement of cholesterol oxide derivatives (also named oxysterols) in the development of cataract. Oxysterol formation can result either from nonenzymatic or enzymatic processes, and some oxysterols can induce a wide range of cytotoxic effects (overproduction of reactive oxygen species (ROS); phospholipidosis) which might contribute to the initiation and progression of cataract. Thus, the conception of molecules capable of regulating cholesterol homeostasia and oxysterol levels in human lens fibers can have some interests and constitute an alternative to surgery at least at early stages of the disease.

Connexin mediated cataract prevention in mice

Cataracts, named for any opacity in the ocular lens, remain the leading cause of vision loss in the world. Non-surgical methods for cataract prevention are still elusive. We have genetically tested whether enhanced lens gap junction communication, provided by increased α3 connexin (Cx46) proteins expressed from α8(Kiα3) knock-in alleles in Gja8^tm1(Gja3)Tww mice, could prevent nuclear cataracts caused by the γB-crystallin S11R mutation in Crygb^S11R/S11R mice. Remarkably, homozygous knock-in α8(Kiα3/Kiα3) mice fully prevented nuclear cataracts, while single knock-in α8(Kiα3/−) allele mice showed variable suppression of nuclear opacities in Crygb^S11R/S11R mutant mice. Cataract prevention was correlated with the suppression of many pathological processes, including crystallin degradation and fiber cell degeneration, as well as preservation of normal calcium levels and stable actin filaments in the lens. This work demonstrates that enhanced intercellular gap junction communication can effectively prevent or delay nuclear cataract formation and suggests that small metabolites transported through gap junction channels protect the stability of crystallin proteins and the cytoskeletal structures in the lens core. Thus, the use of an array of small molecules to promote lens homeostasis may become a feasible non-surgical approach for nuclear cataract prevention in the future.

Effect of estrogen replacement therapy on lens epithelial cell apoptosis in an experimental rat model

Epidemiologic studies have revealed a higher incidence of cataracts in estrogen-deprived postmenopausal women, although the pathogenic mechanism has not yet been elucidated. Apoptosis of lens epithelial cells has been associated with cataractogenesis. The aim of the study reported here was to investigate the effect of estrogen replacement therapy (ERT) on lens epithelial cell apoptosis in an experimental rat model. Forty female Wistar rats were randomized into four groups: ERT (17beta-estradiol, 10 microg/kg/day) for 3 months without ovariectomy (group 1) and with ovariectomy (group 2); only ovariectomy (group 3); sham operated (group 4). At the end of the third month, all rats were sacrificed in estrous cycle, as determined by the vaginal smear test, and their right eyes were enucleated. Enucleated eyes were analyzed by immunohistochemical methods for the expression of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end (TUNEL), caspase-3, and bcl-2 labeling. The TUNEL, caspase-3, and bcl-2 staining scores were found to increase in group 3 rats following the ovariectomy compared to the sham-operated group. The ERT decreased these scores in rats with or without the ovariectomy; however, these differences were not statistically significant. These data suggest that estrogen does not significantly affect lens epithelial cell apoptosis. Further studies are needed to gain a better understanding of the protective mechanism of estrogen and to provide new ideas for the treatment and prevention of cataract.

The structure of the cataract-causing P23T mutant of human gammaD-crystallin exhibits distinctive local conformational and dynamic changes

Crystallins are major proteins of the eye lens and essential for lens transparency. Mutations and aging of crystallins cause cataracts, the predominant cause of blindness in the world. In human γD-crystallin, the P23T mutant is associated with congenital cataracts. Until now, no atomic structural information has been available for this variant. Biophysical analyses of this mutant protein have revealed dramatically reduced solubility compared to that of the wild-type protein due to self-association into higher-molecular weight clusters and aggregates that retain a nativelike conformation within the monomers [Pande, A., et al. (2005) Biochemistry 44, 2491−2500]. To elucidate the structure and local conformation around the mutation site, we have determined the solution structure and characterized the protein’s dynamic behavior by NMR. Although the global structure is very similar to the X-ray structure of wild-type γD-crystallin, pivotal local conformational and dynamic differences are caused by the threonine substitution. In particular, in the P23T mutant, the imidazole ring of His22 switches from the predominant Nε2 tautomer in the wild-type protein to the Nδ1 tautomer, and an altered motional behavior of the associated region in the protein is observed. The data support structural changes that may initiate aggregation or polymerization by the mutant protein.

Phytochelatins inhibit the metal-induced aggregation of alpha-crystallin

Phytochelatins (PCs) are heavy-metal-binding peptides found in some eukaryotes. This study investigates the use of plant-derived PCs for the inhibition of metal-induced protein aggregation. The results of this study show that PCs inhibit zinc-induced alpha-crystallin aggregation, and suggest that PCs might be useful as anti-cataract agents.