Inhibition of selenite-induced cataract by caffeine

Research progress on antioxidants and protein aggregation inhibitors in cataract prevention and therapy (Review)

Cataracts are primarily caused by aging or gene mutations and are the leading cause of blindness globally. As the older population increases, the number of patients with a cataract is expected to grow rapidly. At present, cataract surgery to replace the lens with an artificial intraocular lens is the principal treatment method. However, surgery has several drawbacks, including economic burdens and complications such as inflammation, xerophthalmia, macular edema and posterior capsular opacification. Thus, developing an effective non‑surgical treatment strategy is beneficial to both patients and public health. Mechanistically, cataract formation may be due to various reasons but is primarily initiated and promoted by oxidative stress and is closely associated with crystallin aggregation. In the present review, the current research progress on anti‑cataract drugs, including antioxidants and protein aggregation inhibitors is examined. It summarizes strategies for preventing and treating cataract through cell apoptosis and protein aggregation inhibition while discussing their limitations and further prospects.

Nanomedicine in Ophthalmology: From Bench to Bedside

Ocular diseases such as cataract, refractive error, age-related macular degeneration, glaucoma, and diabetic retinopathy significantly impact vision and quality of life worldwide. Despite advances in conventional treatments, challenges like limited bioavailability, poor patient compliance, and invasive administration methods hinder their effectiveness. Nanomedicine offers a promising solution by enhancing drug delivery to targeted ocular tissues, enabling sustained release, and improving therapeutic outcomes. This review explores the journey of nanomedicine from bench to bedside, focusing on key nanotechnology platforms, preclinical models, and case studies of successful clinical translation. It addresses critical challenges, including pharmacokinetics, regulatory hurdles, and manufacturing scalability, which must be overcome for successful market entry. Additionally, this review highlights safety considerations, current marketed and FDA-approved nanomedicine products, and emerging trends such as gene therapy and personalized approaches. By providing a comprehensive overview of the current landscape and future directions, this article aims to guide researchers, clinicians, and industry stakeholders in advancing the clinical application of nanomedicine in ophthalmology.

The human lens: An antioxidant-dependent tissue revealed by the role of caffeine

Cataract is the leading cause of blindness worldwide and surgery is the only option to treat the disease. Although the surgery is considered to be relatively safe, complications may occur in a subset of patients and access to ophthalmic care may be limited. Due to a growing and ageing population, an increase in cataract prevalence is expected and its management will become a socioeconomic challenge. Hence, there is a need for an alternative to cataract surgery. It is well known that oxidative stress is one of the main pathological processes leading to the generation of the disease. Antioxidant supplementation may, therefore, be a strategy to delay or to prevent the progression of cataract. Caffeine is a widely consumed high-potency antioxidant and may be of interest for the prevention of the disease. This review aims to give an overview of the anatomy and function of the lens, its antioxidant and reactive oxygen species (ROS) composition, and the role of oxidative stress in cataractogenesis. Also, the pharmacokinetics and -dynamics of caffeine will be described and the literature will be reviewed to give an overview of its anti-cataract potential and its possible role in the prevention of the disease.

Single high-dose peroral caffeine intake inhibits ultraviolet radiation-induced apoptosis in human lens epithelial cells in vitro

PURPOSE

The aim of the present study was to determine whether caffeine concentrations in human lens epithelial cells (LECs) achieved from acute peroral caffeine intake inhibit ultraviolet radiation-induced apoptosis in vitro.

METHODS

Patients were planned for cataract surgery of both eyes with a caffeine abstinence of 2 weeks in total, starting 1 week before surgery of the first eye. The second eye was scheduled 1 week after the first eye. At the day of the second eye surgery, patients were given coffee containing 180 mg caffeine shortly before surgery. Lens capsules including LEC, harvested after capsulorhexis, were transferred to a cell culture dish and immediately exposed to close to threshold ultraviolet radiation (UVR). At 24 hr after UVR exposure, apoptotic LECs were analysed by TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining.

RESULTS

TUNEL-positive cells were detected in UVR-exposed lens capsules both after caffeine intake and in controls. The mean difference in TUNEL-positive cells between caffeine intake and contralateral controls (no caffeine) resulted in a 95% CI 15.3 ± 10.4% (degrees of freedom: 16).

CONCLUSION

Peroral caffeine consumption significantly decreased UVR-induced apoptosis in LEC supporting epidemiological findings that caffeine delays the onset of cataract.

Caffeine Uptake into the Vitreous after Peroral Coffee Consumption

INTRODUCTION

Caffeine and its metabolites have antioxidant activity, scavenging reactive oxygen species. The aim of our study was to measure caffeine concentrations in vitreous samples after peroral caffeine intake.

METHODS

This prospective study included patients scheduled for 23-G pars plana vitrectomy with membrane peeling due to epiretinal membranes. The study was performed in two parts: in the first part, patients were recruited into three different groups: group A consisted of habitual coffee drinkers who agreed to drink coffee containing 180 mg caffeine 1 h before surgery (n = 10), group B consisted of habitual coffee drinkers who were not offered coffee before surgery (n = 5), and group C consisted of non-habitual coffee drinkers, forming the control group (n = 5). In the second part (group D) patients (habitual coffee drinkers) agreed to give additional blood serum samples for measurement of caffeine concentration. Harvested samples of vitreous (groups A-D), epiretinal membranes (groups A-C), and blood serum samples (group D) were examined for concentrations of caffeine with gas chromatography-mass spectrometry.

RESULTS

Samples of 40 eyes of 40 patients were harvested. The concentrations of caffeine in the vitreous samples were 1,998 ± 967 ng/mL in group A and 1,108 ± 874 ng/mL in group B. In group C, caffeine concentrations were below 176 ng/mL in all vitreous samples. Both groups A and B had significantly higher concentrations of caffeine in the vitreous samples than group C (p < 0.002, p < 0.01, Mann-Whitney U test). Caffeine concentrations in epiretinal membranes were below the limits of detection. Correlation of caffeine concentrations between blood serum samples and vitreous samples in group D was high, with significantly higher caffeine concentrations in the blood serum.

CONCLUSION

Coffee consumption leads to significant caffeine levels in the vitreous compared to patients in the control group, and caffeine concentrations in the vitreous showed a high correlation to blood serum concentrations of caffeine after peroral coffee consumption.

Effect of caffeine on biomarkers of oxidative stress in lenses of rats with streptozotocin-induced diabetes

INTRODUCTION

One of the major causes of cataract in diabetes is oxidative stress induced by reactive oxygen species (ROS). Nowadays, new substances with antioxidative properties that may prevent cataract development are needed. One such substance is caffeine - an alkaloid with well-documented antioxidative activity.

MATERIAL AND METHODS

The study was conducted on lenses obtained from female rats, divided into 3 groups: control rats; diabetic rats; diabetic rats treated with caffeine at a dose of 20 mg/kg p.o. Type 1 diabetes was induced by streptozotocin (60 mg/kg i.p.). After 4 weeks of caffeine administration, the rats were sacrificed, and the lenses were collected, weighed and homogenized in PBS. The homogenate was used for analysis of protein content, glutathione (GSH) concentration, advanced oxidation protein product (AOPP) concentration, malondialdehyde (MDA) concentration and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx).

RESULTS

The SOD, CAT and GPx activities were found to be higher in the lenses of diabetic rats. There were also increased MDA and AOPP concentrations as well as decreased GSH concentration. The administration of caffeine resulted in decreased activity of SOD, CAT and GPx. The treatment with caffeine also caused an increase of GSH concentration and a decrease of MDA and AOPP concentrations.

CONCLUSIONS

The results of the present study may be of relevance in determining the effect of caffeine on the processes induced by ROS in vivo. Further, they can be an indication for clinical observations aiming at the assessment of both preventive and therapeutic effects of caffeine in cataract.

Ursodeoxycholic acid suppresses the formation of fructose/streptozotocin-induced diabetic cataract in rats

The main objective of this study was to investigate the potential protective effect of ursodeoxycholic acid (UDCA) on fructose/streptozotocin-induced diabetic cataract in rats. The diabetic model (DM) was induced through the administration of 10% fructose in drinking water for 2 weeks followed by streptozotocin injection (intraperitoneal). One week later, hyperglycemia was assisted and diabetic animals were treated with UDCA either as local eye drops (0.5% solution, four times/day) or orally (100 mg/kg b.w.). Cataract formation was monitored biweekly and scored into four stages. After 12 weeks of treatment, rats were subjected to ophthalmological examination, and then, their blood and lenses were prepared for biochemical analysis of glucose, insulin, reduced glutathione, total antioxidant capacity, malondialdehyde, hydrogen peroxide, caspase-12, and lenticular total proteins. In addition, tertiary structure and conformational changes of lenticular soluble proteins were analyzed using SDS-PAGE and UV absorption while changes in lenticular α-crystallin structure were investigated using intrinsic tryptophan fluorescence. Results demonstrated that both local and oral UDCA restored the normal levels of lens T-AOC, MDA, H₂ O₂ , and caspase-12 and improved noticeably the levels of the lens GSH and total proteins. In addition, conformational and tertiary structure changes of soluble lens proteins were significantly reduced in UDCA-treated groups. Morphological examination of lenses revealed decreased score of cataract progression in UDCA-treated groups compared to DM animals. It was concluded that UDCA decreased the incidence of diabetic cataract by maintaining the antioxidant status, reducing the endoplasmic reticulum stress, and suppressing the structural changes of soluble lens proteins.

Adenosine receptor distribution in Rhesus monkey ocular tissue

Adenosine receptor (ADOR) antagonists, such as 7-methylxanthine (7-MX), have been shown to slow myopia progression in humans and animal models. Adenosine receptors are found throughout the body, and regulate the release of neurotransmitters such as dopamine and glutamate. However, the role of adenosine in eye growth is unclear. Evidence suggests that 7-MX increases scleral collagen fibril diameter, hence preventing axial elongation. This study used immunohistochemistry (IHC) and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) to examine the distribution of the four ADORs in the normal monkey eye to help elucidate potential mechanisms of action. Eyes were enucleated from six Rhesus monkeys. Anterior segments and eyecups were separated into components and flash-frozen for RNA extraction or fixed in 4% paraformaldehyde and processed for immunohistochemistry against ADORA1, ADORA2a, ADORA2b, and ADORA3. RNA was reverse-transcribed, and qPCR was performed using custom primers. Relative gene expression was calculated using the ΔΔCt method normalizing to liver expression, and statistical analysis was performed using Relative Expression Software Tool. ADORA1 immunostaining was highest in the iris sphincter muscle, trabecular meshwork, ciliary epithelium, and retinal nerve fiber layer. ADORA2a immunostaining was highest in the corneal epithelium, trabecular meshwork, ciliary epithelium, retinal nerve fiber layer, and scleral fibroblasts. ADORA2b immunostaining was highest in corneal basal epithelium, limbal stem cells, iris sphincter, ciliary muscle, ciliary epithelium, choroid, isolated retinal ganglion cells and scattered scleral fibroblasts. ADORA3 immunostaining was highest in the iris sphincter, ciliary muscle, ciliary epithelium, choroid, isolated retinal ganglion cells, and scleral fibroblasts. Compared to liver mRNA, ADORA1 mRNA was significantly higher in the brain, retina and choroid, and significantly lower in the iris/ciliary body. ADORA2a expression was higher in brain and retina, ADORA2b expression was higher in retina, and ADORA3 was higher in the choroid. In conclusion, immunohistochemistry and RT-qPCR indicated differential patterns of expression of the four adenosine receptors in the ocular tissues of the normal non-human primate. The presence of ADORs in scleral fibroblasts and the choroid may support mechanisms by which ADOR antagonists prevent myopia. The potential effects of ADOR inhibition on both anterior and posterior ocular structures warrant investigation.

Protective effects of Cassia tora leaves in experimental cataract by modulating intracellular communication, membrane co-transporters, energy metabolism and the ubiquitin-proteasome pathway

CONTEXT

Cataract is the clouding of eye lens which causes impairment in vision and accounts for the leading factor of global blindness. Functional food-based prevention of cataract finds application in vision research because of its availability and easy access to all classes of the society. Cassia tora Linn. (Caesalpinaceae) is an edible plant mentioned in the traditional systems of medicine for whole body health, especially to the eyes.

OBJECTIVE

The present study evaluates the potential of ethyl acetate fraction of Cassia tora leaves (ECT) on experimental cataract.

MATERIALS AND METHODS

Cataract was induced by a single subcutaneous injection of sodium selenite (4 μg/g body weight) on 10th day. ECT was supplemented orally from 8th day up to 12th day at a concentration of 5 μg/g body weight and marker parameters were evaluated after 30 days.

RESULTS

The production of MPO and the activation of calpain were reduced 52.17% and 36.67% by ECT in lens tissue, respectively. It modulated the energy status by significantly increasing the activity of CCO 1 (55.56%) and ATP production (41.88%). ECT maintained the ionic balance in the lens by reducing the level of sodium (50%) and increasing the level of potassium (42.5%). It also reduced cell junction modifications and preserved a functional ubiquitin-proteasome pathway.

DISCUSSION AND CONCLUSION

The results reinforce the growing attention on wild plant food resources for preventive protection against cataract. The data suggest the value of Cassia tora leaves as a functional food for ameliorating cataract pathology.

Prevention and reversal of selenite-induced cataracts by N-acetylcysteine amide in Wistar rats

BACKGROUND

The present study sought to evaluate the efficacy of N-acetylcysteine amide (NACA) eye drops in reversing the cataract formation induced by sodium selenite in male Wistar rat pups.

METHODS

Forty male Wistar rat pups were randomly divided into a control group, an N-acetylcysteine amide-only group, a sodium selenite-induced cataract group, and a NACA-treated sodium selenite-induced cataract group. Sodium selenite was injected intraperitoneally on postpartum day 10, whereas N-acetylcysteine amide was injected intraperitoneally on postpartum days 9, 11, and 13 in the respective groups. Cataracts were evaluated at the end of week 2 (postpartum day 14) when the rat pups opened their eyes. N-acetylcysteine amide eye drops were administered beginning on week 3 until the end of week 4 (postpartum days 15 to 30), and the rats were sacrificed at the end of week 4. Lenses were isolated and examined for oxidative stress parameters such as glutathione, lipid peroxidation, and calcium levels along with the glutathione reductase and thioltransferase enzyme activities. Casein zymography and Western blot of m-calpain were performed using the water soluble fraction of lens proteins.

RESULTS

Morphological examination of the lenses in the NACA-treated group indicated that NACA was able to reverse the cataract grade. In addition, glutathione level, thioltransferase activity, m-calpain activity, and m-calpain level (as assessed by Western blot) were all significantly higher in the NACA-treated group than in the sodium selenite-induced cataract group. Furthermore, sodium selenite- injected rat pups had significantly higher levels of malondialdehyde, glutathione reductase enzyme activity, and calcium levels, which were reduced to control levels upon treatment with NACA.

CONCLUSIONS

The data suggest that NACA has the potential to significantly improve vision and decrease the burden of cataract-related loss of function. Prevention and reversal of cataract formation could have a global impact. Development of pharmacological agents like NACA may eventually prevent cataract formation in high-risk populations and may prevent progression of early-stage cataracts. This brings a paradigm shift from expensive surgical treatment of cataracts to relatively inexpensive prevention of vision loss.

Lens: Management of Cataract Surgery, Cataract Prevention, and Floppy Iris Syndrome

According to the World Health Organization, cataract is the major cause of reversible visual impairment in the world. It is present as the cause of decreased visual acuity in 33% of the visual impaired citizens. With the increase of life expectancy in the last decades, the number of patients with cataract is expected to grow for the next 20 years. Nowadays, the only effective treatment for cataracts is surgery and its surgical outcomes have been increasingly satisfactory with the technological advancement.Pharmaceutical development has been also responsible for surgical outcomes enhancement. This includes the development of new ophthalmic viscoelastic devices (OVDs), intraocular dyes, mydriatics, miotics, anesthetics, irrigating solutions, and antibiotics. However, the increased costs and demand for cataract surgery may be hard to meet in the future unless clinical preventive and curative options are evaluated.In this chapter, we review the studies that addressed pharmacological applications in cataract.

Roasting Enhances the Anti-Cataract Effect of Coffee Beans: Ameliorating Selenite-Induced Cataracts in Rats

PURPOSE

Coffee is a widely consumed beverage. While recent studies have linked its intake to a reduced risk of cataracts, caffeine is believed to be the key factor for its effect. To know how roasting beans affects the effect of coffee on cataract formation, we investigated the impact roasting using a selenite-induced cataract rat model.

MATERIALS AND METHODS

Sprague Dawley rats were given a single injection of sodium selenite, which induced formation of nuclear cataracts by day 6, with or without coffee intake (100% coffee, 0.2 mL/day) for following 3 days.

RESULTS

The concentrations of glutathione (GSH) and ascorbic acid (AsA) in selenite-induced cataract lenses declined to half that of controls. However, 3 days of coffee intake ameliorated the reduction of GSH and AsA so that concentrations remained at 70-80% that of controls. Roasting enhanced the preventive effect of coffee by further reducing cataract formation and ameliorating selenite-induced reduction of antioxidants. High-performance liquid chromatography analysis revealed degradation of chlorogenic acid and generation of pyrocatechol during the coffee roasting process. We discovered that pyrocatechol, at doses equivalent to that found in dark-roasted coffee, was equally effective as caffeine at reducing cataract formation and ameliorating the reduction of antioxidants.

CONCLUSION

Our results indicate that pyrocatechol, generated during the roasting process, acts as an antioxidant together with caffeine to prevent cataract formation.

Cassia tora leaves modulates selenite cataract by enhancing antioxidant status and preventing cytoskeletal protein loss in lenses of Sprague Dawley rat pups

ETHNOPHARMACOLOGICAL RELEVANCE

Cataract is the clouding or opacity that develops in the eye's lens and is considered to be an unavoidable consequence of aging due to irreversible lens damage. Free radicals and oxidant species are reported to be the major factor responsible for the onset and pathology of cataract. No pharmacological measures are formulated to treat cataract blindness and surgical removal of the opaque lens is the only remedy till date. Boosting of antioxidant potential of the lens is proved to prevent cataract and many indigenous plants have been screened for anticataractogenic potential in the last decades. The objective of the present study was to determine whether Cassia tora leaves; the plant employed in traditional medicine for eye rejuvenation and ailments, can prevent cataract in neonatal rats.

MATERIALS AND METHODS

Cataract was induced by a single subcutaneous injection of sodium selenite at a dose of 4 μg/g body weight on the 10th day and Cassia tora leaves was administered orally from 8th day upto 12th day at a concentration of 5 μg/g body weight. After 30 days; lens morphology, oxidant-antioxidant equilibrium, glutathione metabolism, cytoskeletal protein/gene expressions were monitored.

RESULTS

Lens morphology, biochemical analysis and expression studies supported the anticataractogenic effect of Cassia tora leaves.

CONCLUSION

In summary, it can be suggested that the consumption of these leaves afford protection to the lens with its antioxidant action and seems to be a new therapeutic approach against cataract by preventive protection.

Effect of coffee (caffeine) against human cataract blindness

Previous biochemical and morphological studies with animal experiments have demonstrated that caffeine given topically or orally to certain experimental animal models has significant inhibitory effect on cataract formation. The present studies were undertaken to examine if there is a correlation between coffee drinking and incidence of cataract blindness in human beings. That has been found to be the case. Incidence of cataract blindness was found to be significantly lower in groups consuming higher amounts of coffee in comparison to the groups with lower coffee intake. Mechanistically, the caffeine effect could be multifactorial, involving its antioxidant as well as its bioenergetic effects on the lens.

Inhibitory Effect of Crocin(s) on Lens α-Crystallin Glycation and Aggregation, Results in the Decrease of the Risk of Diabetic Cataract

The current study investigates the inhibitory effect of crocin(s), also known as saffron apocarotenoids, on protein glycation and aggregation in diabetic rats, and α-crystallin glycation. Thus, crocin(s) were administered by intraperitoneal injection to normal and streptozotocin-induced diabetic rats. The cataract progression was recorded regularly every two weeks and was classified into four stages. After eight weeks, the animals were sacrificed and the parameters involved in the cataract formation were measured in the animal lenses. Some parameters were also determined in the serum and blood of the rats. In addition, the effect of crocin(s) on the structure and chaperone activity of α-crystallin in the presence of glucose was studied by different methods. Crocin(s) lowered serum glucose levels of diabetic rats and effectively maintained plasma total antioxidants, glutathione levels and catalase activity in the lens of the animals. In the in vitro study, crocin(s) inhibited α-crystallin glycation and aggregation. Advanced glycation end products fluorescence, hydrophobicity and protein cross-links were also decreased in the presence of crocin(s). In addition, the decreased chaperone activity of α-crystallin in the presence of glucose changed and became close to the native value by the addition of crocin(s) in the medium. Crocin(s) thus showed a powerful inhibitory effect on α-crystallin glycation and preserved the structure-function of this protein. Crocin(s) also showed the beneficial effects on prevention of diabetic cataract.

Grape seed extract and zinc containing nutritional food supplement prevents onset and progression of age-related cataract in wistar rats

OBJECTIVE

To study possible inhibition of oxidative stress and cataract formation by single combined formulation of grape seed extract and Zincovit tablets against sodium selenite-induced age-related cataract in Wistar rat pups.

METHODS

Oxidative stress and consequent cataract formation was induced by subcutaneous administration of a single dose of sodium selenite (10 µmoles/kg) to Wistar rat pups on day 7 post-natally. In experiments designed to inhibit such cataract formation, the pups were pretreated subcutaneously with combined formulation of grape seed extract and Zincovit tablets (40, 80 and 160 mg/kg), one day prior to the administration of selenite and continuing such treatment till day 20, when the experiments were terminated. The extent of tissue damage caused by the selenite was assessed biochemically by measurements of the levels of reduced glutathione, glutathione peroxidase, glucose-6-phosphate dehydrogenase, protein thiol, catalase, superoxide dismutase, malondialdehyde, aldose reductase, sorbitol dehydrogenase and adenosine triphosphate in the isolated lenses. Cataract formation and its prevention were monitored by examining the eye with pen light illumination and subsequent photography of the isolated lenses.

RESULTS

Injection of selenite led to a significant loss of lens clarity due to cataract formation. In the group treated with combined formulation of grape seed extract and Zincovit tablets, the formation of cataract was significantly prevented. In the normal and selenite induced senile cataract control group, the levels of lens oxidative stress markers, G6PD and ATP were substantially lower than in the grape seed extract with Zincovit tablets treated group (p < 0.05).

CONCLUSION

Over all, the results suggest that single combined formulation of grape seed extract and Zincovit tablets may offer a prophylactic measure against onset and progression of age- related cataract of human subjects as nutritional food supplement.

Sulforaphane-induced transcription of thioredoxin reductase in lens: possible significance against cataract formation

PURPOSE

Sulforaphane is a phytochemically derived organic isothiocyanate 1-isothiocyanato-4-methylsulfinyl-butane present naturally in crucifers, including broccoli and cauliflower. Biochemically, it has been reported to induce the transcription of several antioxidant enzymes. Since such enzymes have been implicated in preventing cataract formation triggered by the intraocular generation of oxy-radical species, the purpose of this investigation was to examine whether it could induce the formation of antioxidant enzymes in the eye lens. Thioredoxin reductase (TrxR) was used as the target of such induction.

METHODS

Mice lenses were cultured for an overnight period of 17 hours in medium 199 fortified with 10% fetal calf serum. Incubation was conducted in the absence and presence of sulforaphane (5 μM). Subsequently, the lenses were homogenized in phosphate-buffered saline (PBS), followed by centrifugation. TrxR activity was determined in the supernatant by measuring the nicotinamide adenine dinucleotide phosphate (reduced) (NADPH)-dependent reduction of 5,5'-dithiobis-2-nitrobenzoic acid (DTNB). Non-specific reduction of DTNB was corrected for by conducting parallel determinations in the presence of aurothiomalate. The reduction of DTNB was followed spectrophotometrically at 410 nm.

RESULTS

The activity of TrxR in the lenses incubated with sulforaphane was found to be elevated to 18 times of that observed in lenses incubated without sulforaphane. It was also noticeably higher in the lenses incubated without sulforaphane than in the un-incubated fresh lenses. However, this increase was much lower than that observed for lenses incubated with sulforaphane.

CONCLUSION

Sulforaphane has been found to enhance TrxR activity in the mouse lens in culture. In view of the protective effect of the antioxidant enzymes and certain nutrients against cataract formation, the findings suggest that it would, by virtue of its ability to enhance the activity of such enzymes, prevent the tissue against oxidative stress that leads to cataract formation. Additional studies with the activities of other antioxidant enzymes such as quinone oxidoreductase and the levels of Nrf2 are in progress.

Cataract prevalence and prevention in Europe: a literature review

This literature review is aimed at the evaluation of the potential for cataract prevention in Europe. It was performed using PubMed with Mesh and free-text terms. Studies included were (i) performed on a population of Caucasian origin at an age range of 40-95 years, (ii) cataract was clinically verified, (iii) drug record of prescriptions, their indication, a record of every diagnosis, dosage and quantity of prescribed medicine were available, (iv) sample size >300 and (v) published between 1990 and 2009. The results of 29 articles were reviewed. Former [3.75 (2.26-6.21)] or current smoking [2.34 (1.07-5.15)], diabetes of duration >10 years [2.72 (1.72-4.28)], asthma or chronic bronchitis [2.04 (1.04-3.81)], and cardiovascular disease [1.96 (1.22-3.14)] increased the risk of cataract. Cataract was more common in patients taking chlorpromazine during ≥90 days with a dosage ≥300 mg [8.8 (3.1-25.1)] and corticosteroids >5 years [3.25 (1.39-7.58)] in a daily dose >1600 mg [1.69 (1.17-2.43)]. Intake of a multivitamin/mineral formulation [2.00 (1.35-2.98)] or corticosteroids [2.12 (1.93-2.33)] also increased the risk of cataract. Corticosteroids applied orally [3.25 (1.39-7.58)], parenteral [1.56 (1.34-1.82)] or inhalational [1.58 (1.46-1.71)] lead to cataract more frequently than those applied topically: nasal [1.33 (1.21-1.45)], ear [1.31 (1.19-1.45)] or skin [1.43 (1.36-1.50)]. Outpatient cataract surgery was negatively associated with total cataract surgery costs, and chlorpromazine, corticosteroids and multivitamin/mineral formation increase the risk of posterior subcapsular cataract dependent on dose, treatment application and duration. This review presented a comprehensive overview of specific and general cataract risk factors and an update on most recent experimental studies and randomized control trials directed at cataract prevention.

C-phycocyanin modulates selenite-induced cataractogenesis in rats

The present investigation is aimed to evaluate the anticataractogenic potential of C-phycocyanin (C-PC), extracted and purified from Spirulina platensis. Enucleated rat lenses were maintained in vitro in Dulbecco's modified Eagle medium (DMEM). Group I contained DMEM, Group II and Group III contained 100 μM of sodium selenite, Group III was subdivided into three viz IIIa, IIIb, IIIc supplemented with 100, 150, 200 μg of C-PC respectively. In the in vivo study, on tenth day post partum: Group I rat pups received an intraperitoneal injection of saline, Group II, IIIa, IIIb, and IIIc rat pups received a subcutaneous injection of sodium selenite (19 μmol/kg bodyweight) Group IIIa, IIIb, IIIc also received an intraperitoneal injection of 100, 150, 200 mg/kg body weight of C-PC, respectively, from postpartum days 9-14. On termination of the experiment, the lenses from both in vitro and in vivo studies were subjected to morphological examination and subsequently processed to estimate the activities of antioxidant enzymes namely superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, levels of reduced glutathione and lipid peroxidation products. Sodium selenite-exposed, C-PC-treated rat lenses (Group IIIc), showed significant restoration of antioxidant enzyme activity (p < 0.05) when compared to their counterpart Group II. Group IIIc conserved the levels of GSH and lipid peroxidation products at near to normal levels as compared with Group II. Results conclude the possible role of C-PC in modulating the antioxidant enzyme status, thereby retarding sodium selenite-induced cataract incidence both in vitro and in vivo.

Protein misfolding and aggregation in cataract disease and prospects for prevention

The transparency of the eye lens depends on maintaining the native tertiary structures and solubility of the lens crystallin proteins over a lifetime. Cataract, the leading cause of blindness worldwide, is caused by protein aggregation within the protected lens environment. With age, covalent protein damage accumulates through pathways thought to include UV radiation, oxidation, deamidation, and truncations. Experiments suggest that the resulting protein destabilization leads to partially unfolded, aggregation-prone intermediates and the formation of insoluble, light-scattering protein aggregates. These aggregates either include or overwhelm the protein chaperone content of the lens. Here, we review the causes of cataract and nonsurgical methods being investigated to inhibit or delay cataract development, including natural product-based therapies, modulators of oxidation, and protein aggregation inhibitors.

Ursodeoxycholic acid prevents selenite-induced oxidative stress and alleviates cataract formation: In vitro and in vivo studies

OBJECTIVE

To evaluate the antioxidative and anticataractogenic potential effect of ursodeoxycholic acid (UDCA) on selenite-induced cataract in vitro and in vivo.

METHODS

Enucleated rat lenses were incubated in M199 medium alone (Group I), with 200 μM selenite (Group II), or with 200 μM selenite and 500 μM UDCA (Group III). Selenite was administered on the third day and UDCA treatment was from the second to the fifth day. The development of cataracts was observed under an inverted microscope. Total antioxidative capabilities (T-AOC), mean activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (Gpx), glutathione reductase (GR) and glutathione S-transferase (GST), levels of reduced glutathione (GSH), malondialdehyde (MDA), and total sulfhydryl content were analyzed in lenticular samples. In vivo, cataracts were induced in 12-day-old pups by single subcutaneous injections of sodium selenite. The test groups received 180 mg/kg bodyweight/day of UDCA intraperitoneally on postpartum days 11-16 or 0.5% UDCA drops four times daily on postpartum days 11-25.

RESULTS

In vitro, morphological examination of the lenses revealed dense vacuolization and opacification in Group II, minimal vacuolization in 12.5% of Group III, and no opacification in 87.5% of Group III. In Group I, all lenses were clear. UDCA significantly (p<0.05) restored GSH and total sulfhydryl, and decreased MDA levels. T-AOC and the mean activities of the antioxidant enzymes were elevated following treatment with UDCA. In vivo, 0.5% UDCA drops resulted in only 20% nuclear cataract development and 180 mg/kg of UDCA intraperitoneally led to 50% development, compared to 100% in the control group (p<0.05).

CONCLUSIONS

UDCA prevents selenite toxicity and cataractogenesis by maintaining antioxidant status and GSH, protecting the sulfhydryl group, and inhibiting lipid peroxidation in lenses.

Role of ultraviolet irradiation and oxidative stress in cataract formation-medical prevention by nutritional antioxidants and metabolic agonists

PURPOSE

Cataract is a significant cause of visual disability with relatively high incidence. It has been proposed that such high incidence is related to oxidative stress induced by continued intraocular penetration of light and consequent photochemical generation of reactive oxygen species, such as superoxide and singlet oxygen and their derivatization to other oxidants, such as hydrogen peroxide and hydroxyl radical. The latter two can also interact to generate singlet oxygen by Haber-Weiss reaction. It has been proposed that in addition to the endogenous enzymatic antioxidant enzymes, the process can be inhibited by many nutritional and metabolic oxyradical scavengers, such as ascorbate, vitamin E, pyruvate, and xanthine alkaloids, such as caffeine.

METHODS

Initial verification of the hypothesis has been done primarily by rat and mouse lens organ culture studies under ambient as well as ultraviolet (UV) light irradiation and determining the effect of such irradiation on its physiology in terms of its efficiency of active membrane transport activity and the levels of certain metabolites such as glutathione and adenosine triphosphate as well as in terms of apoptotic cell death. In vivo studies on the possible prevention of oxidative stress and cataract formation have been conducted by administering pyruvate and caffeine orally in drinking water and by their topical application using diabetic and galactosemic animal models.

RESULTS

Photosensitized damage to lens caused by exposure to visible light and UVA has been found to be significantly prevented by ascorbate and pyruvate. Caffeine has been found be effective against UVA and UVB. Oral or topical application of pyruvate has been found to inhibit the formation of cataracts induced by diabetes and galactosemia. Caffeine has also been found to inhibit cataract induced by sodium selenite and high levels of galactose. Studies with diabetes are in progress.

CONCLUSIONS

Various in vitro and in vivo studies summarized in this review strongly support the hypothesis that light penetration into the eye is a significant contributory factor in the genesis of cataracts. The major effect is through photochemical generation of reactive oxygen species and consequent oxidative stress to the tissue. The results demonstrate that this can be averted by the use of various antioxidants administered preferably by topical route. That they will be so effective is strongly suggested by the effectiveness of pyruvate and caffeine administered topically to diabetic and galactosemic animals.

Protective effects and mechanism of tetramethylpyrazine against lens opacification induced by sodium selenite in rats

Tetramethylpyrazine (TMP), extracted from the Chinese herbal medicine Ligusticum wallichii franchat (chuan xiong in Chinese), is a potent anti-free radical and calcium antagonist. Correspondingly, two important hypotheses in the causation of cataracts are free radical toxicity and calcium ion overload. In this study we investigated the effect of TMP on lens opacification induced by sodium selenite in rats, addressing the potential of TMP eye drops to prevent and treat cataracts. Results showed that the extent of lens opacification in the untreated Normal Control group (NC group) was significantly less than that of selenite-injected untreated rats (MC group) on days 3, 5, 7 and 10 (p < 0.001), while TMP treated selenite-injected rats (TMP group) had less lens opacification than the MC group on days 3, 5, 7 and 10 (p < 0.05). Compared with the NC group, the MC group had significantly decreased activity of super-oxide dismutase (SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) and significantly elevated malondialdehyde (MDA) and calcium ion content (p < 0.001). Compared with the MC group, the activity of (SOD), (GSH-PX) and (CAT) were significantly higher while (MDA) and calcium ion levels were significantly lower in the TMP group at all time points (p < 0.01). The findings demonstrate that the selenite-induced cataract rat models were successfully built and the TMP eye drops can delay lens opacification induced by sodium selenite in rats. The mechanism by which TMP preserves lens transparency from selenite treated animals is associated with the lenses' ability to maintain normal levels of activity of SOD, GSH-PX and CAT and normal concentrations of MDA and calcium ion.

Effectiveness of topical caffeine in cataract prevention: studies with galactose cataract

PURPOSE

The primary objective of the study was to investigate the possible inhibition of cataract formation by topical administration of caffeine using the galactosemic rat model. It was hypothesized that caffeine will do so by acting as scavenger of reactive oxygen species known to be generated under hyperglycemic conditions.

METHODS

Cataract was induced by feeding young rats a diet containing 24% galactose for a period of 25 days. A control group of such rats was treated with a placebo eye drop preparation containing hydroxy propyl methyl cellulose as a wetting agent. In the experimental group, the rats were treated with the above preparation mixed with 72 mM caffeine.

RESULTS

Administration of caffeine eye drops was found to significantly inhibit the onset as well as the progress of cataract formation. By day 25 on the galactose diet, all the animals in the control group developed advanced white opacity spread over the entire area of the lens. In the caffeine group, the formation of such opacity remained strikingly inhibited. The lenses remained largely transparent. The transparency data paralleled the higher concentration of glutathione maintained by caffeine treatment. Its levels in the placebo group were 0.8, 0.5, and 0.4 µmoles/g lens wt. on days 5, 15, and 25 against a consistent basal control value of ~3 µmoles/g over the entire period. In the caffeine group, the corresponding values were nearly 3 µmoles/g till day 15, but decreasing to ~2 µmoles/g on day 25. The levels were hence significantly higher than in the caffeine untreated group, remaining relatively closer to the basal controls. In addition, the compound was found effective in inhibiting morphological changes induced by galactose.

CONCLUSIONS

Micromolar amounts of topical caffeine have been found to be significantly effective in inhibiting the formation of galactose cataract, strongly suggesting its possible usefulness against diabetic cataracts. The effects are attributed to its ability to prevent oxidative stress and consequent maintenance of tissue metabolic and transport functions, in addition to preventing the induction of apoptosis.