Oxidative damage and the prevention of age-related cataracts

Age-related eye disease and gender

Worldwide, the prevalence of moderate to severe visual impairment and blindness is 285 millions, with 65% of visually impaired and 82% of all blind people being 50 years and older. Meta-analyses have shown that two out of three blind people are women, a gender discrepancy that holds true for both developed and developing countries. Cataract accounts for more than half of all blindness globally and gender inequity in access to cataract surgery is the major cause of the higher prevalence of blindness in women. In addition to gender differences in cataract surgical coverage, population-based studies on the prevalence of lens opacities indicate that women have a higher risk of developing cataract. Laboratory as well as epidemiologic studies suggest that estrogen may confer antioxidative protection against cataractogenesis, but the withdrawal effect of estrogen in menopause leads to increased risk of cataract in women. For the other major age-related eye diseases; glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy, data are inconclusive. Due to anatomic factors, angle closure glaucoma is more common in women, whereas the dominating glaucoma type; primary open-angle glaucoma (POAG), is more prevalent in men. Diabetic retinopathy also has a male predominance and vascular/circulatory factors have been implied both in diabetic retinopathy and in POAG. For AMD, data on gender differences are conflicting although some studies indicate increased prevalence of drusen and neovascular AMD in women. To conclude, both biologic and socioeconomic factors must be considered when investigating causes of gender differences in the prevalence of age-related eye disease.

The Relationship Between Serum 25-Hydroxyvitamin D Levels and Nuclear Cataract in the Carotenoid Age-Related Eye Study (CAREDS), an Ancillary Study of the Women's Health Initiative

PURPOSE

To investigate the relationship between serum 25-hydroxyvitamin D (25[OH]D) levels and nuclear cataract among participants of the Carotenoids in Age-Related Eye Disease Study (CAREDS), an ancillary study of the Women's Health Initiative (WHI) Observational Study (OS).

METHODS

Nuclear cataract was assessed from slit lamp photographs (2001-2004) taken 6 years after collecting serum analyzed for 25(OH)D levels at WHI baseline (1994-1998) in 1278 CAREDS participants age 50 to 79 years. Multivariate (age, iris color, smoking, pulse pressure) odds ratios (ORs) for nuclear cataract (nuclear opacities > level 4 or cataract extraction) by quintiles of serum 25(OH)D were estimated using logistic regression.

RESULTS

No significant association was observed between serum 25(OH)D and nuclear cataract among women of all ages (age-adjusted OR [95% confidence interval (CI)] 0.97 [0.65-1.45]). However, there was a significant age interaction (P for interaction = 0.04). There were no significant associations in the women 70 years or older. In women younger than 70 years, we observed an inverse association between serum 25(OH)D and nuclear cataract (multivariate adjusted ORs [95% CI] 0.54 [0.29-0.99] and 0.66 [0.36-1.20] for quintiles 4 and 5 vs. 1, respectively; P = 0.03). Further adjustment for 25(OH)D determinants (body mass index, vitamin D intake, and UVB exposure) attenuated this association.

CONCLUSIONS

Serum 25(OH)D levels were unrelated to nuclear opacities in this study sample. However, exploratory analyses suggest a protective association in women younger than 70 years. Further investigations of the relationship between vitamin D and nuclear lens opacities are warranted.

Different amounts of alcohol consumption and cataract: a meta-analysis

PURPOSE

To evaluate the association between different amounts of alcohol consumption and the risk of age-related cataract.

METHODS

We searched PubMed and Embase from their inception until May 2014 for case-control or cohort studies with data on alcohol consumption and age-related cataract. Heavy alcohol consumption was defined as more than two standard drinks per day, which is equal to a daily intake of 20 g of alcohol or 140 g per week. Moderate consumption was defined as less than 20 g of alcohol per day but more than never any. We performed separate meta-analyses for the associations of moderate or heavy alcohol consumption with age-related cataract under a random-effects model, respectively.

RESULTS

Five case-control and five cohort studies were identified through comprehensive literature search. In the meta-analysis of 10 studies, the associations between moderate alcohol consumption and age-related cataract were marginally nonsignificant (pooled relative risk, 0.88; 95% confidence interval, 0.74 to 1.05; I = 82.1%), whereas heavy alcohol consumption was associated with an increased risk of age-related cataract (pooled relative risk, 1.26; 95% confidence interval, 1.06 to 1.50; I = 58.9%). The association between heavy alcohol consumption and cataract was stronger in case-control than in cohort studies. Adjusting for smoking as a potential confounder attenuated the association between heavy alcohol consumption and cataract.

CONCLUSIONS

Heavy alcohol consumption significantly increased the risk of age-related cataract, whereas moderate consumption may be protective for this ocular condition. Clinically, information on a patient's alcohol drinking history might be valuable to general physicians and ophthalmologists when there is a diagnosis of age-related cataract and should be collected on a routine basis in eye clinics.

The Gender-Dependent Association between Obesity and Age-Related Cataracts in Middle-Aged Korean Adults

The aim of this study was to investigate the association of central and abdominal obesity with the prevalence of cataracts in a middle-aged Korean population. This retrospective cross-sectional study was based on the data collected from the Korea National Health and Nutrition Examination Survey 2008–2009, in which 4,914 subjects were examined. Ophthalmological examinations were performed to determine the presence of a nuclear, cortical, or posterior subcapsular cataract. Both general obesity (a body mass index ≥25 kg/m²) and abdominal obesity (a waist circumference ≥90 cm for men and ≥80 cm for women) were significantly associated with the occurrence of cataracts among middle-aged women [adjusted odds ratio (aOR), 1.32; 95% confidence interval (CI), 1.03–1.69; and aOR, 1.40; 95% CI, 1.06–1.85, respectively], while abdominal obesity was significantly inversely associated with the occurrence of cataracts among middle-aged men (aOR, 0.76; 95% CI, 0.58–1.01; and aOR, 0.66; 95% CI, 0.49–0.89, respectively). We report a difference in the association between obesity and the prevalence of cataracts based on gender.

Targeted deletion of the murine Lgr4 gene decreases lens epithelial cell resistance to oxidative stress and induces age-related cataract formation

Oxidative stress contributes to the formation of cataracts. The leucine rich repeat containing G protein-coupled receptor 4 (LGR4, also known as GPR48), is important in many developmental processes. Since deletion of Lgr4 has previously been shown to lead to cataract formation in mice, we sought to determine the specific role that Lgr4 plays in the formation of cataracts. Initially, the lens opacities of Lgr4(-/-) mice at different ages without ocular anterior segment dysgenesis (ASD) were evaluated with slit-lamp biomicroscopy. Lenses from both Lgr4(-/-) and wild-type mice were subjected to oxidation induced protein denaturation to assess the ability of the lens to withstand oxidation. The expression of antioxidant enzymes was evaluated with real-time quantitative PCR. Phenotypically, Lgr4(-/-) mice showed earlier onset of lens opacification and higher incidence of cataract formation compared with wild-type mice of similar age. In addition, Lgr4(-/-) mice demonstrated increased sensitivity to environmental oxidative damage, as evidenced by altered protein expression. Real-time quantitative PCR showed that two prominent antioxidant defense enzymes, catalase (CAT) and superoxidase dismutase-1 (SOD1), were significantly decreased in the lens epithelial cells of Lgr4(-/-) mice. Our results suggest that the deletion of Lgr4 can lead to premature cataract formation, as well as progressive deterioration with aging. Oxidative stress and altered expression of several antioxidant defense enzymes contribute to the formation of cataracts.

αA-crystallin gene CpG islands hypermethylation in nuclear cataract after pars plana vitrectomy

PURPOSE

To investigate the DNA methylation status of αA-crystallin gene in cataract secondary to pars plana vitrectomy.

METHODS

Anterior capsular membranes of 40 eyes of 40 patients with cataract secondary to vitrectomy were collected. Another 20 eyes of 20 patients who received pars plana vitrectomy and phacoemulsification in the primary procedure, were recruited as control. Methylation status of the CpG islands of αA-crystallin gene was analyzed by pyrosequencing. Expression of αA-crystallin was evaluated by real-time polymerase chain reaction and western blot.

RESULTS

In the post vitrectomy group, five patients with posterior subcapsular opacity and four patients with cortical opacity were excluded from further analysis. The remaining 31 patients with nuclear cataract were assigned into two groups according to tamponade types: 19 of octafluoropropane (C3F8) and 12 of silicone oil (SiO). The average nuclear color grading was elevated both in C3F8 and SiO groups after vitrectomy. Compared to the control group, hypermethylation of the CpG islands in the αA-crystallin gene promoter was found in both post vitrectomy groups, accompanied by significantly reduced αA-crystallin expression. No statistically significant differences were found between the C3F8 and SiO groups either for DNA methylation status or αA-crystallin expression.

CONCLUSIONS

CpG islands hypermethylation of αA-crystallin gene may be involved in nuclear cataract formation after pars plana vitrectomy.

Acetylated 8-oxoguanine DNA glycosylase 1 and its relationship with p300 and SIRT1 in lens epithelium cells from age-related cataract

The human 8-oxoguanine-DNA glycosylase 1 (OGG1) is the major DNA glycosylase responsible for repair of 7,8-dihydro-8-oxoguanine (8-oxoG) and ring-opened fapyguanine, critical mutagenic DNA lesions that are induced by reactive oxygen species. OGG1 acetylation has been demonstrated playing an important role in response to DNA damage. Here, we investigated the relationship between acetylated OGG1 (Ac-OGG1) and ARC, and clarified the effect of p300 and SIRT1 on the 8-oxoG excision ability of OGG1 in ARC development. Our results showed that anterior lens capsules from ARC group had higher proportion of 8-oxoG positive LECs than those from control group. OGG1 mRNA and protein levels significantly increased in ARC group compared with control group, while the protein levels of Ac-OGG1 were lower in ARC group. We investigated the factors involved in OGG1 acetylation and found that p300 and SIRT1 are the major acetyltransferases for OGG1 acetylation. We also identified acetylation of K338/K341 lysine residues in OGG1 has an important role on the repair activity of OGG1 to oxidative damage after H2O2 exposure in human lens epithelial cells (HLE-B3). Taken together, these data demonstrate that OGG1 acetylation regulates its function in response to DNA damage and could be one of the mechanisms of ARC.

Carotenoids: potential allies of cardiovascular health?

Carotenoids are a class of natural, fat-soluble pigments found principally in plants. They have potential antioxidant biological properties because of their chemical structure and interaction with biological membranes. Epidemiologic studies supported the hypothesis that antioxidants could be used as an inexpensive means of both primary and secondary cardiovascular disease (CVD) prevention. In fact, the oxidation of low-density lipoproteins (LDL) in the vessels plays a key role in the development of atherosclerotic lesions. The resistance of LDL to oxidation is increased by high dietary antioxidant intake, so that carotenoids, as part of food patterns such as the Mediterranean diet, may have beneficial effects on cardiovascular health too. Further properties of carotenoids leading to a potential reduction of cardiovascular risk are represented by lowering of blood pressure, reduction of pro-inflammatory cytokines and markers of inflammation (such as C-reactive protein), and improvement of insulin sensitivity in muscle, liver, and adipose tissues. In addition, recent nutrigenomics studies have focused on the exceptional ability of carotenoids in modulating the expression of specific genes involved in cell metabolism. The aim of this review is to focus attention to this effect of some carotenoids to prevent CVD.

Free radicals: properties, sources, targets, and their implication in various diseases

Free radicals and other oxidants have gained importance in the field of biology due to their central role in various physiological conditions as well as their implication in a diverse range of diseases. The free radicals, both the reactive oxygen species (ROS) and reactive nitrogen species (RNS), are derived from both endogenous sources (mitochondria, peroxisomes, endoplasmic reticulum, phagocytic cells etc.) and exogenous sources (pollution, alcohol, tobacco smoke, heavy metals, transition metals, industrial solvents, pesticides, certain drugs like halothane, paracetamol, and radiation). Free radicals can adversely affect various important classes of biological molecules such as nucleic acids, lipids, and proteins, thereby altering the normal redox status leading to increased oxidative stress. The free radicals induced oxidative stress has been reported to be involved in several diseased conditions such as diabetes mellitus, neurodegenerative disorders (Parkinson's disease-PD, Alzheimer's disease-AD and Multiple sclerosis-MS), cardiovascular diseases (atherosclerosis and hypertension), respiratory diseases (asthma), cataract development, rheumatoid arthritis and in various cancers (colorectal, prostate, breast, lung, bladder cancers). This review deals with chemistry, formation and sources, and molecular targets of free radicals and it provides a brief overview on the pathogenesis of various diseased conditions caused by ROS/RNS.

Polymorphisms of DNA repair genes XPD (Lys751Gln) and XRCC1 (Arg399Gln), and the risk of age-related cataract: a meta-analysis

PURPOSE

A meta-analysis of available studies was used to test the association between two DNA repair genes and age-related cataract.

MATERIALS AND METHODS

A systematic search of the Chinese National Knowledge Infrastructure, EMBASE and PubMed databases identified six studies that were analyzed. Meta-analysis was used to evaluate single nucleotide polymorphisms (SNP) of the DNA repair gene xeroderma pigmentosum complementation group D (XPD) (Lys751Gln) and the X-ray repair cross-complementing gene 1 (XRCC1) (Arg399Gln). Only articles published before June 6, 2014, were included. The quality of the studies was determined using Newcastle-Ottawa Scale tools. The summary odds ratio (OR) and corresponding confidence interval (CI) for XPD Lys751Gln and XRCC1 Arg399Gln polymorphisms and risk of age-related cataract were estimated by random and fixed-effects models. Sensitivity analysis was employed to determine the robustness of the conclusions.

RESULTS

Six studies, with a total of 1518 patients with cataractous lenses and 1437 subjects with clear lenses, were included in the meta-analysis. XRCC1 Arg399Gln polymorphisms were associated with cataract risk (recessive model: ORfixed = 0.79, 95% CI: 0.67-0.93; dominant model: ORfixed = 0.84, 95% CI: 0.64-1.11; additive model: ORfixed = 0.82, 95% CI: 0.72-0.92). Analysis of Chinese, but not non-Chinese subgroups, confirmed this association. The OR of XPD Lys751Gln polymorphisms for cataract was not significant. The associations remained significant after sensitivity analysis.

CONCLUSIONS

This meta-analysis indicates that XRCC1 Arg399Gln polymorphisms, but not XPD Lys751Gln polymorphisms, are associated with risk of age-related cataract.

Gender and cataract--the role of estrogen

There is evidence from epidemiologic data that cataract is more common in women than men. This is not solely due to a higher rate of cataract extraction in women, as is the case in the western world, but several population-based studies show that females have a higher prevalence of lens opacities, especially cortical. There is no firm evidence that lifestyle-related factors are the cause of this gender discrepancy. Focus has therefore been directed towards the role of estrogen in cataract formation. Although data on endogenous and exogenous estrogen involvement in cataractogenesis are conflicting, some studies have indicated that hormone therapy may decrease the risk of cataract and thus be protective. It has been hypothesized that the decrease in estrogen at menopause cause increased risk of cataract in women, i.e. not strictly the concentration of estrogen, but more the withdrawal effect. Estrogens are known to exert several anti-aging effects that may explain the longer lifespan in women, including metabolically beneficial effects, neuroprotection, preservation of telomeres and anti-oxidative properties. Since oxidative stress is considered important in cataractogenesis, studies have investigated the effects of estrogens on lens epithelial cells in culture or in animal models. Several investigators have found protection by physiological concentrations of 17β-estradiol against oxidative stress induced by H2O2 in cultured lens epithelial cells. Although both main types of estrogen receptors, ERα and ERβ, have been demonstrated in lens epithelium, most studies so far indicate that the estrogen-mediated protection in the lens is exerted through non-genomic, i.e. receptor-independent mechanisms, possibly through phosphorylation of extracellular signal-regulated kinase (ERK1/ERK2), a member of the mitogen-activated protein kinase (MAPK)-signaling pathway. Further studies are needed, both epidemiologic as to the role of hormone therapies, and laboratory studies regarding molecular estrogen-mediated mechanisms, in order to comprehend the role of estrogens on cataract formation.

Overweight, obesity, and age-related cataract: a meta-analysis

PURPOSE

To examine the longitudinal association of overweight/obesity with age-related cataract.

METHODS

A systematic review of the literature was performed using PubMed and Embase from their inception until June 2013 for prospective data on body mass index categories identical or similar to the World Health Organization-recommended classifications of body weight and age-related cataract including nuclear, cortical, and posterior subcapsular (PSC) cataract. Meta-analyses were conducted using random-effects models with results reported as adjusted relative risks (RRs).

RESULTS

A total of 163,013 subjects aged 40 to 84 years from six prospective cohort studies were included in the meta-analysis. Obesity was associated with an increasing risk of nuclear cataract (pooled RR, 1.12; 95% confidence interval [CI], 1.02 to 1.25), cortical cataract (pooled RR, 1.34; 95% CI, 1.07 to 1.66), and PSC cataract (pooled RR, 1.52; 95% CI, 1.31 to 1.77). Overweight was only associated with an increasing risk of PSC cataract (pooled RR, 1.23; 95% CI, 1.09 to 1.40).

CONCLUSIONS

The longitudinal associations of obesity with incident age-related cataract are confirmed by the findings in this six-study meta-analysis. The association of obesity with PSC cataract is stronger than that with nuclear or cortical cataract. Randomized control trials are warranted to examine the effectiveness and cost-effectiveness of weight reduction in obese populations to decrease the risk of age-related cataract.

Body mass index and risk of age-related cataract: a meta-analysis of prospective cohort studies

Background

Age-related cataract (ARC) is the leading cause of blindness in the world. The relationship between body mass index (BMI) and risk of ARC is controversial across observational studies. We therefore performed this meta-analysis to evaluate the association between BMI and risk of ARC.

Methods

Eligible studies were identified through an electronic search of PubMed, Embase and the Cochrane Library. We pooled study-specific relative risks (RRs) and 95% confidence intervals (CIs) to determine the risk of ARC associated with BMI categories and per 1 kg/m² increase in BMI.

Results

A total of 17 prospective cohort studies were included in the meta-analysis. The pooled RRs of ARC were 1.08 (95% CI, 1.01–1.16) for overweight and 1.19 (95% CI, 1.10–1.28) for obesity compared with normal weight. These findings were robust when stratified by sex, sample source, outcome types and confounders, while significantly differed by assessment of BMI and ARC, and duration of follow-up. The summary RR suggested that per 1 kg/m² increase in BMI was associated with a 2% increased risk of ARC (RR 1.02, 95% CI 1.01–1.03). Pooled estimates of RRs consistently indicated a trend for subjects with a high BMI to develop posterior subcapsular cataracts (RR 1.19, 95% CI 1.06–1.35, for overweight; RR 1.50, 95% CI 1.24–1.81, for obesity; RR 1.04, 95% CI 1.01–1.06, per 1 kg/m² increase in BMI) other than nuclear or cortical cataracts.

Conclusions

The overall findings suggest that elevated BMI may increase the risk of ARC, especially posterior subcapsular cataracts. Further trials are needed to investigate the effect of weight reduction in obese populations on the risk of ARC.

Tyrosine/cysteine cluster sensitizing human γD-crystallin to ultraviolet radiation-induced photoaggregation in vitro

Ultraviolet radiation (UVR) exposure is a major risk factor for age-related cataract, a protein-aggregation disease of the human lens often involving the major proteins of the lens, the crystallins. γD-Crystallin (HγD-Crys) is abundant in the nucleus of the human lens, and its folding and aggregation have been extensively studied. Previous work showed that HγD-Crys photoaggregates in vitro upon exposure to UVA/UVB light and that its conserved tryptophans are not required for aggregation. Surprisingly, the tryptophan residues play a photoprotective role because of a distinctive energy-transfer mechanism. HγD-Crys also contains 14 tyrosine residues, 12 of which are organized as six pairs. We investigated the role of the tyrosines of HγD-Crys by replacing pairs with alanines and monitoring photoaggregation using light scattering and SDS-PAGE. Mutating both tyrosines in the Y16/Y28 pair to alanine slowed the formation of light-scattering aggregates. Further mutant studies implicated Y16 as important for photoaggregation. Mass spectrometry revealed that C18, in contact with Y16, is heavily oxidized during UVR exposure. Analysis of multiple mutant proteins by mass spectrometry suggested that Y16 and C18 likely participate in the same photochemical process. The data suggest an initial photoaggregation pathway for HγD-Crys in which excited-state Y16 interacts with C18, initiating radical polymerization.

Measuring the viscosity of whole bovine lens using a fiber optic oxygen sensing system

PURPOSE

To obtain a better understanding of oxygen and nutrient transport within the lens, the viscosity of whole lenses was investigated using a fiber optic oxygen sensor (optode). The diffusion coefficient of oxygen was calculated using the Stokes-Einstein equation at the slip boundary condition.

METHODS

The optode was used to measure the oxygen decay signal in samples consisting of different glycerol/water solutions with known viscosities. The oxygen decay signal was fitted to a double exponential decay rate equation, and the lifetimes (tau) were calculated. It was determined that the tau-viscosity relationship is linear, which served as the standard curve. The same procedure was applied to fresh bovine lenses, and the unknown viscosity of the bovine lens was calculated from the tau-viscosity relationship.

RESULTS

The average viscosity in a whole bovine lens was determined to be 5.74 ± 0.88 cP by our method. Using the Stokes-Einstein equation at the slip boundary condition, the diffusion coefficient for oxygen was calculated to be 8.2 × 10(-6) cm(2)/s.

CONCLUSIONS

These data indicate a higher resistance to flow for oxygen and nutrients in the lens than what is currently assumed in the literature. Overall, this study allows a better understanding of oxygen transport within the lens.

Association between lutein and zeaxanthin status and the risk of cataract: a meta-analysis

The purpose of this meta-analysis was to evaluate the relationship between blood lutein and zeaxanthin concentration and the risk of age-related cataract (ARC). MEDLINE, EMBASE, ISI and Cochrane Library were searched to identify relevant studies up to April 2013. Meta-analysis was conducted to obtain pooled relative risks (RRs) for the highest-versus-lowest categories of blood lutein and zeaxanthin concentrations. One cohort study and seven cross-sectional studies were included in the meta-analysis. There were significant inverse associations between nuclear cataract and blood lutein and zeaxanthin concentrations, with the pooled RRs ranging from 0.63 (95% confidence interval (CI): 0.49, 0.77) for zeaxanthin to 0.73 (95% CI: 0.59, 0.87) for lutein. A stronger association between nuclear cataract and blood zeaxanthin might be noted for the studies conducted in the European Nations. Blood lutein and zeaxanthin were also noted to lead towards a decrease in the risk of cortical cataract and subcapsular cataract; however, these pooled RRs were not statistically significant, with the exception of a marginal association between lutein and subcapsular cataract. Our results suggest that high blood lutein and zeaxanthin are significantly associated with a decrease in the risk of nuclear cataract. However, no significant associations were found for ARC in other regions of the lens.

DNA damage in lens epithelial cells and peripheral lymphocytes from age-related cataract patients

BACKGROUND

Oxidative DNA damage may be one of the etiologies of age-related cataract (ARC). We quantified DNA damage in lens epithelial cells (LECs) and peripheral blood lymphocytes of ARC.

METHODS

A total of 64 patients with different types of ARC and 23 control subjects were enrolled. Fresh LECs and peripheral lymphocytes were collected and DNA damage was evaluated by alkaline comet assay. The percentage of DNA in the tail of comets (%Tail DNA) and the olive tail moment (OTM) were calculated by CASP software.

RESULTS

The results showed the %Tail DNA and OTM in LECs and lymphocytes in the overall cataract patient group were significantly higher than those in the control subjects. The %Tail DNA and OTM of LECs and lymphocytes showed no differences among cortical, nuclear and posterior subcapsular cataracts. The %Tail DNA and OTM in LECs were significantly lower than those in lymphocytes but a significant correlation of the DNA damage was found between them.

CONCLUSION

We concluded that DNA damage in lens and peripheral blood lymphocytes increased in ARC. The results imply that local and systemic oxidative DNA damage might play certain roles in ARC pathogenesis.

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.

Hydrogen saline prevents selenite-induced cataract in rats

PURPOSE

The aim of this study was to investigate the potential antioxidative effect and mechanism for the protective effects of hydrogen saline on selenite-induced cataract in rats.

METHODS

Sprague-Dawley rat pups were divided into the following groups: control (Group A), selenite induced (Group B), and selenite plus hydrogen saline treated (Group C). Rat pups in Groups B and C received a single subcutaneous injection of sodium selenite (25 μmol/kg bodyweight) on postnatal day 12. Group C also received an intraperitoneal injection of H2 saline (5 ml/kg bodyweight) daily from postnatal day 8 to postnatal day 17. The development of cataract was assessed weekly by slit-lamp examination for 2 weeks. After sacrifice, extricated lenses were analyzed for activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase, levels of malondialdehyde, reduced glutathione (GSH), and total sulfhydryl contents.

RESULTS

The magnitude of lens opacification in Group B was significantly higher than in Group A (p<0.05), while Group C had less opacification than Group B (p<0.05). Compared with Group B, the mean activities of the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase, levels of GSH, and total sulfhydryl contents were higher, whereas the level of malondialdehyde was lower following treatment with hydrogen saline(p<0.05).

CONCLUSIONS

This is an initial report showing that hydrogen saline can prevent selenite-induced cataract in rats. It acts via maintaining antioxidant enzymes and GSH, protecting the sulfhydryl group, and inhibiting lipid peroxidation.

Oxidative responses induced by pharmacologic vitreolysis and/or long-term hyperoxia treatment in rat lenses

PURPOSE

The aim of the study was to investigate the protective effects of intact vitreous gel on the lens after pharmacologic vitreolysis and hyperoxia exposure in rats in vivo.

METHODS

Eyes of Sprague-Dawley rats were induced to posterior vitreous detachment (PVD) by pharmacologic vitreolysis, and the rats with and without PVD were treated with hyperoxia 3 h per day for 5 months. Lens transparency was monitored by a slit-lamp biomicroscope. A series of biochemical measurements were made in extracts of the lens cortex and nucleus. Ascorbate levels were measured in the aqueous and vitreous humors.

RESULTS

No significant differences in lens transparency or morphology were observed in all groups, and no significant biochemical changes were observed in the cortex or nucleus of lenses of the PVD group. In the lens nucleus, the values of water-soluble protein concentration in PVD + hyperoxia group were lower than that of the PVD group. The levels of water-soluble proteins, glutathione (GSH) and ascorbate decreased in the hyperoxia group with an intact vitreous body. Vitreolysis enhanced the effect of hyperoxia, decreasing soluble protein, GSH and ascorbate below the levels seen in eyes with vitreolysis alone. The levels of antioxidants and soluble proteins were lower in the lens nucleus, and the effects of vitreolysis plus hyperoxia were more significant in the nucleus. Hyperoxia and hyperoxia plus vitreolysis reduced catalase activity and increased oxidized GSH to a greater extent in the lens cortex, although these treatments increased protein-GSH mixed disulfides in both regions. Long-term hyperoxia also lowered ascorbate levels in the vitreous and aqueous humors, an effect that was enhanced by vitreolysis.

CONCLUSIONS

Exposure to excess molecular oxygen produces significant oxidative damage to the lens, especially the lens nucleus. These effects were enhanced by pharmacologic vitreolysis, indicating that intact vitreous gel protects the lens from oxidative damage.

Shotgun proteomic analysis of S-thiolation sites of guinea pig lens nuclear crystallins following oxidative stress in vivo

PURPOSE

To compare levels of S-glutathiolation and S-cysteinylation occurring at more than 60 cysteine residues of 12 different guinea pig lens water-soluble nuclear crystallins following treatment of the animals with hyperbaric oxygen (HBO).

METHODS

Guinea pigs (initially 18 months old) were treated 30X (3X per week for 10 weeks) with HBO (2.5 atm 100% O(2) for 2.5 h) as a model to study the formation of nuclear cataract. This treatment produces a moderate increase in lens nuclear light scatter (compared to denser scatter occurring after 80 HBO treatments), with five- to sixfold increases in levels of protein-bound glutathione (PSSG) and protein-bound cysteine (PSSC). Trypsin digests of lens nuclear water-soluble proteins were analyzed with two-dimensional liquid chromatography and mass spectrometry to identify specific cysteine residues binding either glutathione or cysteine. Lens nuclei of age-matched untreated animals were used as controls.

RESULTS

All major crystallins, except αB, were modified to some extent by either S-glutathiolation or S-cysteinylation. Overall, 72% of the cysteine residues of guinea pig lens nuclear crystallins were shown to be capable of binding glutathione, cysteine, or both molecules. The crystallin with the highest level of modification was βA1/A3 (six of eight -SH groups), and that with the lowest (two of five -SH groups) was βA2. O(2)-induced increases in PSSG levels were 2.8, 2.4, and 4.1 times control for γA-, γB-, and γC-crystallins, respectively. Comparable increases in PSSC levels for the three γ-crystallins were 2.3, 2.7, and 2.4 times control, respectively. βB2-crystallin showed the highest amount of O(2)-induced PSSG formation of any of the crystallins, as well as a substantial level of control PSSG, and nearly all of this was due to a single residue, C67, a site also present in human βB2-crystallin. Overall, 32 of the 44 modified cysteine residues were homologous with the human.

CONCLUSIONS

This large-scale study successfully identified lens crystallin cysteine residues that bound glutathione and/or cysteine under normal or oxidative stress conditions. The high percentage of protein -SH groups that are modified by S-thiolation in the guinea pig lens nucleus demonstrates the substantial protein sulfhydryl redox buffer capability present in the center of the lens. The results suggest that PSSG and PSSC formation may act to delay O(2)-induced insolubilization of γA-, γB-, and γC-crystallins, and β-crystallins, but with a greater effect on the γ-crystallins at an early stage of oxidative stress. The study has shown that technological approaches are now available to investigate in considerable detail the role of specific lens -SH groups in nuclear cataractogenesis.

Preventive effect of danshensu on selenite-induced cataractogenesis in cultured rat lens

BACKGROUND

To investigate the preventive effect of danshensu on the selenite-induced opacification of cultured rat lenses.

METHODS

Isolated lens were divided into three groups with eight lenses in each group. Group I: lenses were incubated with M199 medium alone; Group II: incubated in M199 containing 200 µmol/L sodium selenite; Group III: incubated in M199 containing 200 µmol/L sodium selenite and 500 µmol/L danshensu. Selenite was administered on the third day, and danshensu treatment was from the second to the fifth day. Cataracts development was observed using an inverted microscope, and the lenses were analysed for total anti-oxidative capabilities, mean activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase; levels of reduced glutathione; malondialdehyde; and total sulfhydryl content.

RESULTS

All lenses in Group I were clear, whereas all lenses in Group II developed dense vacuolization and opacification. In Group III, 25% lenses revealed minimal vacuolization, and 75% showed no opacification or vacuolization. Total anti-oxidative capabilities and the mean activities of anti-oxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase; levels of glutathione; and total sulfhydryl content were elevated, and the level of malondialdehyde was decreased following treatment with danshensu compared with Group II.

CONCLUSION

The anti-oxidative properties of danshensu may play a major role in its contribution to the anticataract effect.

Vitreous levels of oxidative stress biomarkers and the radical-scavenger α1-microglobulin/A1M in human rhegmatogenous retinal detachment

PURPOSE

To explore oxidative stress and the radical scavenger α(1)-microglobulin (A1M) in the vitreous body of human eyes with primary rhegmatogenous retinal detachment (RRD).

METHODS

Levels of carbonyl groups, a marker of oxidative stress, and A1M were measured by ELISA and RIA in 14 vitreous samples derived from patients suffering from RRD, and compared with 14 samples from macula hole (MH) patients. Carbonyl group and A1M levels in RRD samples were statistically related to detachment characteristics. Analysis of total protein level, SDS-PAGE, and Western blotting of A1M was also performed. In a separate experiment, mRNA expression of A1M was measured by RT-PCR in rat retina explants.

RESULTS

Levels of carbonyl groups and A1M varied widely in RRD vitreous samples, but were significantly higher in samples derived from eyes with large detachment area and macula-off status, while the presence of vitreous hemorrhage did not show any significant correlation. Compared with MH samples, RRD samples displayed significantly higher levels of A1M, whereas changes in total protein levels and carbonyl groups were not significant. Novel forms of A1M, not previously seen in plasma, were found in the vitreous body by Western blotting. Furthermore, A1M expression was seen in rat retina explants and was upregulated after 24 h of culturing.

CONCLUSION

Oxidative stress is a prominent feature of human eyes with primary RRD, and is directly related to detachment severity. Affected eyes can launch a protective response in the form of the radical scavenger A1M possibly derived from the retina. The results thus indicate potential therapeutic cell loss prevention in RRD by employing the endogeneous radical scavenger A1M.

Risk factors for incident cortical, nuclear, posterior subcapsular, and mixed lens opacities: the Los Angeles Latino eye study

PURPOSE

To identify sociodemographic and biological risk factors associated with the 4-year incidence of nuclear, cortical, posterior subcapsular (PSC), and mixed lens opacities.

DESIGN

Population-based, longitudinal study.

PARTICIPANTS

We included 4658 Latinos ≥40 years from 6 census tracts in Los Angeles, California.

METHODS

Participants underwent an interview and detailed eye examination, including best-corrected visual acuity and slit-lamp assessment of lens opacities using the Lens Opacities Classification System II (LOCS II) at baseline and again 4 years later. Each opacity type was defined in persons with a LOCS II score of ≥2. Univariate and forward stepwise logistic regression analyses were used to identify independent baseline risk factors associated with 4-year incidence of nuclear only, cortical only, PSC only, and mixed (when >1 opacity type developed in a person) lens opacities. These comprised 4 mutually exclusive groups, and were based on person rather than eye.

MAIN OUTCOME MEASURES

Odds ratios for independent risk factors associated with 4-year incidence of nuclear-only, cortical-only, PSC-only, and mixed lens opacities.

RESULTS

Of the 3471 participants with gradable lenses in the same eye at baseline and 4-year follow-up, 200 (5.8%) had incident nuclear-only opacities, 151 (4.1%) had incident cortical-only opacities, 16 (0.5%) had incident PSC-only lens opacities, and 88 (2.5%) had mixed lens opacities. Independent baseline risk factors for incident nuclear-only lens opacities included older age, current smoking, and presence of diabetes. Independent risk factors for incident cortical-only lens opacities included older age and having diabetes at baseline. Female gender was an independent risk factor for incident PSC-only lens opacities. Older age and presence of diabetes at baseline examination were independent risk factors for incident mixed lens opacities. Specifically, in diabetics, higher levels of hemoglobin A1c was associated with greater risk for 4-year incident nuclear-only, cortical-only and mixed lens opacities.

CONCLUSIONS

Improved diabetic control and smoking prevention may reduce the risk of developing lens opacities. Understanding both modifiable and nonmodifiable risk factors provides insight into the development of lens opacification.

Developmental truncations of connexin 50 by caspases adaptively regulate gap junctions/hemichannels and protect lens cells against ultraviolet radiation

The gap junction-forming connexin (Cx) 50 is truncated gradually during lens development. Premature cleavage of lens connexins is thought to be associated with cataract formation. We have shown previously that Cx50 is likely to be cleaved by caspase-3 like protease during chick lens development. Here, using HPLC-electrospray tandem mass spectrometry, we mapped two cleavage sites at the C terminus of Cx50 after Glu-368 and Asp-379 and identified caspase-3 and caspase-1 as the responsible proteases, respectively. The activity of caspase-1, like caspase-3, was detected in the outer cortex increased during lens development, which coincided with the accumulation of the truncated fragments of Cx50 in the core region of the lens. The truncated Cx50 fragments present in older lenses were reproduced in the younger lens after treatment with UV radiation; this cleavage could be partially blocked by caspase-1/3-specific inhibitors. Interestingly, as compared with full-length Cx50, caspase-truncated Cx50 showed a dramatic decrease in gap junction coupling and a loss of hemichannel function. Furthermore, expression of caspase-truncated Cx50 fragments increased cell viability against UV radiation as compared with full-length Cx50. Together, these results suggest that both caspase-1 and -3 are responsible for the cleavage at the C terminus of Cx50 during lens development. The reduction of gap junction coupling and closure of hemichannels formed by truncated Cx50 are likely to adaptively protect cells against elevated oxidative stress associated with lens aging.

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.

Lutein and zeaxanthin supplementation reduces H2O2-induced oxidative damage in human lens epithelial cells

PURPOSE

Epidemiological studies suggest that dietary intake of lutein and zeaxanthin is inversely related to the risk for senile cataract. The objectives of this work were to investigate the mechanisms by which these nutrients provide anti-cataract effects. We evaluated their modulation of oxidative damage in human lens epithelial cells (HLEC) and their interaction with intracellular glutathione (GSH).

METHODS

Subconfluent HLEC were pre-incubated with or without 5 µM lutein, zeaxanthin, or α-tocopherol for 48 h and then exposed to 100 µM H(2)O(2) for 1 h. Levels of protein carbonyls in the cells were measured by western-blotting analysis following reaction with 2,4-dinitrophenylhydrazine (DNPH). Levels of malondialdehyde (MDA), reduced glutathione (GSH) and oxidized glutathione (GSSG) were measured by an HPLC system. DNA damage was assessed using comet assays. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay.

RESULTS

In the absence of H(2)O(2), HLEC had very low levels of protein carbonyl and MDA. Supplementation with lutein, zeaxanthin, or α-tocopherol to the unstressed HLEC had no detectable effects on levels of oxidized proteins and lipid in the cells. Exposure of HLEC to H(2)O(2) significantly increased levels of oxidized proteins, lipid peroxidation, and DNA damage. Pre-incubation with lutein, zeaxanthin, or α-tocopherol dramatically reduced the levels of H(2)O(2) -induced protein carbonyl, MDA, and DNA damage in HLEC. The protective effects of lutein, zeaxanthin, and α-tocopherol against protein oxidation, lipid peroxidation, and DNA damage were comparable. Supplementation with lutein, zeaxanthin, or α-tocopherol increased GSH levels and GSH:GSSG ratio, particularly in response to oxidative stress. Depletion of GSH resulted in significant increase in susceptibility to H(2)O(2)-induced cell death. Supplementation with α-tocopherol, but not lutein or zeaxanthin, can partially restore the resistance of GSH-depleted cells to H(2)O(2).

CONCLUSIONS

These data indicate that lutein or zeaxanthin supplementation protects lens protein, lipid, and DNA from oxidative damage and improves intracellular redox status upon oxidative stress. The protective effects are comparable to that of α-tocopherol, except that lutein and zeaxanthin cannot compensate for GSH depletion. The data imply that sufficient intake of lutein and zeaxanthin may reduce the risk for senile cataract via protecting the lens from oxidative damage.

Up-regulation of NDRG2 in senescent lens epithelial cells contributes to age-related cataract in human

Background

Human N-Myc downstream regulated gene2 (NDRG2), a novel gene has been cloned and shown to be related to a number of cellular processes, including proliferation, differentiation, stress, and apoptosis. NDRG2 has also been linked to age-related Alzheimer's disease. Since the role of this gene in senescence is limited, we have investigated the potential role of NDRG2 in human lens epithelial cells (HLECs), a paradigm implicated in age-related cataract.

Methodology/Principal Findings

Cultured HLECs (SRA01/04) were subjected to prolonged exposure to low dose of H₂O₂ to simulate senescence. After being exposed to 50 µM H₂O₂ for 2 weeks, HLECs senescent-morphological changes appeared, cell viability decreased dramatically, cell proliferation reduced from 37.4% to 16.1%, and senescence-associated β-galactosidase activity increased from 0 to 90.3%. Ndrg2 protein expression was also significantly increased in these senescent cells. To induce overexpression of NDRG2, SRA01/04 cells were infected with the adenoviral vector of NDRG2. In these cells, overexpression of NDRG2 resulted in a fibroblast-like appearance and the cell viability decreased about 20%. In addition, the NDRG2-overexpression cells demonstrated 20% lower viability when exposed to 50–200 µM H₂O₂ for acute oxidative stress. Furthermore, the expression of NDRG2 from age-related cataracts was up-regulated 2-fold at both mRNA and protein levels compared with the clear lenses.

Conclusions/Significance

NDRG2 is up regulated not only in the ageing process of HLECs in vitro but also in the cells from human age-related cortical cataract in vivo. Up-regulation of NDRG2 induces cell morphological changes, reduces cell viability, and especially lowers cellular resistance to oxidative stress. NDRG2-mediated affects in HLECs may associate with age-related cataract formation.

Binding of γ-crystallin substrate prevents the binding of copper and zinc ions to the molecular chaperone α-crystallin

α-Crystallin is a small heat shock protein and molecular chaperone. Binding of Cu2+ and Zn2+ ions to α-crystallin leads to enhanced chaperone function. Sequestration of Cu2+ by α-crystallin prevents metal-ion mediated oxidation. Here we show that binding of human γD-crystallin (HGD, a natural substrate) to human αA-crystallin (HAA) is inversely related to the binding of Cu2+/Zn2+ ions: The higher the amount of bound HGD, the lower the amount of bound metal ions. Thus, in the aging lens, depletion of free HAA will not only lower chaperone capacity but also lower Cu2+ sequestration, thereby promoting oxidation and cataract.