Oxidative stress on lens and cataract formation: role of light and oxygen

2001 assessment of nutritional influences on risk for cataract

It is clear that oxidative stress is associated with compromises to the lens. Recent literature indicates that antioxidants may ameliorate that risk and may actually decrease risk for cataract. This article will briefly review the etiology of cataract. It will also review the epidemiologic information with emphasis on roles for vitamins C and E and carotenoids. More thorough recent reviews are available.

N-Acetylcarnosine, a natural histidine-containing dipeptide, as a potent ophthalmic drug in treatment of human cataracts

A study was designed to document and quantify the changes in lens clarity over 6 and 24 months in 2 groups of 49 volunteers (76 eyes) with an average age of 65.3 +/- 7.0 enrolled at the time of diagnosis of senile cataracts of minimal to advanced opacification. The patients received N-acetylcarnosine, 1% sol (NAC) (26 patients, 41 eyes = Group II), placebo composition (13 patients, 21 eyes) topically (two drops, twice daily) to the conjunctival sac, or were untreated (10 patients, 14 eyes); the placebo and untreated groups were combined into the control (reference) Group I. Patients were evaluated upon entry, at 2-month (Trial 1) and 6-month (Trial 2)-intervals for best corrected visual acuity (b/c VA), by ophthalmoscopy and the original techniques of glare test (for Trial 1), stereocinematographic slit-image and retro-illumination photography with subsequent scanning of the lens. The computerized interactive digital analysis of obtained images displayed the light scattering/absorbing centers of the lens into 2-D and 3-D scales. The intra-reader reproducibility of measuring techniques for cataractous changes was good, with the overall average of correlation coefficients for the image analytical data 0.830 and the glare test readings 0.998. Compared with the baseline examination, over 6 months 41.5% of the eyes treated with NAC presented a significant improvement of the gross transmissivity degree of lenses computed from the images, 90.0% of the eyes showed a gradual improvement in b/c VA to 7-100% and 88.9% of the eyes ranged a 27-100% improvement in glare sensitivity. Topographic studies demonstrated less density and corresponding areas of opacification in posterior subcapsular and cortical morphological regions of the lens consistent with VA up to 0.3. The total study period over 24 months revealed that the beneficial effect of NAC is sustainable. No cases resulted in a worsening of VA and image analytical readings of lenses in the NAC-treated group of patients. In most of the patients drug tolerance was good. Group I of patients demonstrated the variability in the densitometric readings of the lens cloudings, negative advance in glare sensitivity over 6 months and gradual deterioration of VA and gross transmissivity of lenses over 24 months compared with the baseline and 6-month follow-up examinations. Statistical analysis revealed the significant differences over 6 and 24 months in cumulative positive changes of overall characteristics of cataracts in the NAC-treated Group II from the control Group I. The N-acetylated form of natural dipeptide L-carnosine appears to be suitable and physiologically acceptable for nonsurgical treatment for senile cataracts.

The eye in cystic fibrosis

PURPOSE

To investigate modifications of ocular surface and lens transparency in patients with cystic fibrosis in relation to the stage of digestive insufficiency.

METHODS

Forty consecutive patients with cystic fibrosis and 24 age- and sex-matched healthy volunteers were examined. The tear tests (Schirmer's basic test, tear film break-up time) and conjunctival exfoliative cytology (CC) were used to study the ocular surface. The lens transparency was measured with the Opacity Lens Meter 701 (OLM 701, Interzeag AG, Switzerland). Digestive insufficiency was evaluated by the steatocrit method.

RESULTS

Significant changes in conjunctival cytology and lens opacity, and abnormal tear tests were detected in CF patients; the alterations were more pronounced in patients with severe digestive insufficiency.

CONCLUSIONS

Cystic fibrosis patients present ocular surface abnormalities and lens transparency modifications and their severity is related to the digestive insufficiency. Simple, rapid and non-invasive tear tests and cytological procedures might be used as additional tests for assessing the severity of cystic fibrosis.

Growth factor receptor gene and protein expressions in the human lens

In this study the mRNAs encoding epidermal growth factor receptor (EGFR), basic fibroblast growth factor receptor (FGFR-2) and insulin-like growth factor receptor (IGFR-1) genes of the human normal lenses at ages varying from 0.5 to 72 years, were identified by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Regulation of EGFR gene expression in the lens did not change with aging, and of FGFR-2 and IGFR-1 genes also remained unaltered up to age 53 years. However, expressions of FGFR-2 and IGFR-1 genes were decreased at ages above 60 years. EGFR, FGFR-2 and IGFR-1 proteins were detected by immunoblot analysis in the epithelial cell membranes of lens at age varying from 40 to 72 years. There was no detectable amount of EGFR protein in fiber cell membranes of the lens, and the levels of FGFR-2 and IGFR-1 proteins were much lower than those in the epithelial cell membranes. The low levels of these receptor proteins in the fiber cell membranes of lens, suggest their possible role in keeping the differentiated function of these unique transparent cells. The findings of the increased protein levels with age of EGFR with the appearance of some degradation products at age 48 years and higher, and the increased FGFR-2 protein at age 60 years and higher in the epithelial cell membranes of lens, were of interest. It appears that this could be a compensatory protective response of the lens to aging process for lifelong continuation of normal growth by proliferation and differentiation of its epithelial cells into new fiber cells in the germinative zone at the equatorial region. Thus, these results could provide a basis for further studies on growth factor receptor gene and protein regulations in the mechanism of lens aging and progression of age-related human cataract.

Modelling cortical cataractogenesis 22: is in vitro reduction of damage in model diabetic rat cataract by taurine due to its antioxidant activity?

The protective effect of taurine in model in vitro diabetic cataract and the mechanism of this effect were investigated in isolated rat lenses. Isolated rat lenses were incubated in medium 199 in elevated glucose (55.6 m m) with taurine (5 m m). Taurine concentrations in the lenses were determined by amino acid analysis. Accumulative leakage of the intracellular enzyme lactate dehydrogenase (LDH) was used to estimate damage to the lens, as previously reported. In the clear lenses, prior to vacuole formation, after 1 or 2 days of incubation, the taurine and amino acids in lenses decreased progressively in concentration. In lenses incubated with 5 m m taurine, the level of taurine was increased towards that of control lenses. In taurine-treated lenses LDH leakage was significantly decreased, and lens clarity was maintained, similarly to that found previously for vitamin C and lipoic acid. To test whether taurine has similar antioxidant activity, we tested its ability to decrease luminol luminescence generated by (1) superoxide from hypoxanthine/xanthine oxidase and (2) peroxide from diluted glucose/glucose oxidase. For either superoxide or peroxide, the luminescence was decreased to zero, as a function of increasing taurine concentration, at 30 m m, approximately the physiological concentration of taurine in the lens. Spin trapping confirmed that taurine scavenged superoxide. This is consistent with a role for taurine as an important antioxidant protecting the lens against oxidative insults. Amino acids also had antioxidant activity in this assay, and as a group, when all activities were summed, their loss also contributed significantly to the antioxidant loss. Taken in conjunction with Wolff and Crabbe's observation of increased free radical generation by glucose auto-oxidation in diabetes, this suggests a push-pull mechanism for increased oxidative stress in diabetic cataract, involving both increased free radicals and decreased radical scavenging antioxidants.

Modelling cortical cataractogenesis 21: in diabetic rat lenses taurine supplementation partially reduces damage resulting from osmotic compensation leading to osmolyte loss and antioxidant depletion

The concentration of taurine and the amino acids, glutathione, cysteine, ascorbate and ATP were determined in the lenses of rats made diabetic with streptozotocin. In the clear lenses, prior to vacuole formation after 1 or 2 weeks of diabetes, the increase in concentration of sorbitol and the total decrease of all these osmolytes were not significantly different. The major components of the osmolytes lost were taurine and amino acids, which together accounted for over 75% of the total osmolyte loss. Since glutathione, ascorbate, taurine and cysteine have been reported to have antioxidant activity, it appears that their loss may potentiate damage occurring as a result of free radicals generated by nonenzymic glycation by the Maillard reaction. Amino acids also lost as a result of the osmotic compensation, are estimated to be responsible for almost half of the antioxidant activity lost. To test this hypothesis, normal and streptozotocin diabetic female Wistar rats were given taurine at 0.05% or 0.10% (w/w) in the diet. This treatment resulted in small only marginally significant increases in serum taurine levels. At the end of 6 weeks the rats were examined for weight gain or loss and at the time of killing, blood was collected for measurement of serum glucose. gamma-Crystallin levels were determined in vitreous and aqueous humours using a radioimmunoassay. A lens from each rat was homogenized in 8 m guanidinium chloride for adenosine triphosphate (ATP) analysis. In normal rats, a small amount of gamma-crystallin was found in the vitreous humour, and an even smaller amount in the aqueous humour. Diabetes caused a 4- to 5-fold increase in the vitreous humour and a 4-fold increase in gamma-crystallin in the aqueous humour. Diabetes also led to a significant worsening in general body condition, loss of body weight, formation of cataracts, and decrease in lens ATP levels. Addition of taurine to the diet of diabetic animals resulted in a significant decrease of gamma-crystallin leakage into the vitreous but not the aqueous humour. Taurine had no effect on the lens ATP levels. Neither streptozotocin diabetes nor taurine in the diet appeared to affect the weight of the lenses.

Biochemical changes induced by intravitreally-injected doxorubicin in the iris-ciliary body and lens of the rabbit eye

The aim of this study was to examine the chronic effects and mode of action of doxorubicin in ocular tissues. A dose of 10 microg (17.24 nanomoles) of doxorubicin hydrochloride in 20 microl sterile saline were intravitreally injected, under local anaesthesia, in one eye of 13 rabbits and 50 microg (86.20 nanomoles) were similarly injected in one eye of 3 rabbits. The contralateral eye received 20 microl of saline only. The dose of 50 microg induced initially mild uveal inflammation which became chronic and turned into circular iritis. Both doses of the drug induced cataract of the lens and clouding of the cornea within 2-3 months. The activity of superoxide dismutase, in iris-ciliary bodies and lenses treated with either 10 or 50 microg of the compound, was significantly lower relative to that in respective control tissues. In contrast to superoxide dismutase, catalase showed an increased activity in experimental tissues relative to control. The lysosomal hydrolases acid phosphatase, N-acetyl-B-D-glucosaminidase, aryl sulphatase and acid cathepsin, all showed significantly elevated activities in iris-ciliary body tissues one year after injection with the 50 microg doxorubicin. The reduction in superoxide dismutase activity may render ocular tissues susceptible to peroxidative attack and the increased activities of lysosomal hydrolases may contribute to chronic cell injury and inflammation.

Effect of oxidation on Ca2+ -ATPase activity and membrane lipids in lens epithelial microsomes

Membrane oxidation may contribute to cataractogenesis. In our pursuit to understand the etiology of cataracts, we assessed the effect of membrane oxidation products on the activity of the lens epithelium calcium pump. Microsome preparations from bovine lens epithelium were oxidized to varying degrees with a ferrous and ferric ascorbate system to generate hydrogen peroxide and superoxide. Ca2+ -ATPase activity was measured using a colorometric assay. Lipid oxidation was quantified by infrared spectroscopy. Ca2+ -ATPase activity decreased as a function of ascorbate concentration between 0 and 200 microM. The level of Ca2+ -ATPase inhibition was correlated to both the level of lipid oxidation and the degree of lipid hydrocarbon chain order. At 25 degrees C when lipids are more ordered, the Ca2+ -ATPase activity was similar to that observed in the oxidized system measured at 37 degrees C. Glutathione, mercaptoethanol, and iodoacetate were able to reverse the oxidative inhibition of the calcium pump, suggesting that the ascorbate/iron oxidant directly oxidized the protein sulfhydryl moieties. To further probe the mechanism of Ca2+ ATPase inhibition, hydrogen peroxide was used to oxidize muscle sarcoplasmic reticulum Ca2+ -ATPase reconstituted in its native lipid vesicles, egg phosphatidylcholine, and dihydrosphingomyelin, with saturated hydrocarbon chains. In these systems, oxidation inhibited the Ca2+ -ATPase pump by 60-80%. There was no statistical difference between the level of oxidative inhibition and the percentage of dihydrosphingomyelin. Because dihydrosphingomyelin cannot be oxidized, whereas egg phosphatidylcholine (PC) can, and because the percentage of inhibition was the same for reconstituted systems using either lipid, the mechanism of inhibition is likely not via a secondary process involving oxidation-induced lipid structural changes or products of lipid oxidation.

A possible role for vitamin C in age-related cataract

While many experimental studies have shown a protective effect of vitamin C in age-related cataract, other studies have revealed contrasting roles for this nutrient. Oxidative damage in the lens can be prevented by vitamin C. However, a pro-oxidant effect of vitamin C through H2O2 generation has been suggested. Vitamin C has also been shown to play a role in protein glycation, which is observed in cataract formation. A protective effect of dietary energy restriction appears to be inversely related to plasma vitamin C levels in rodents. Moreover, conclusions from human epidemiological and intervention studies are not uniform. The available evidence suggests that maintenance of sufficient plasma vitamin C is needed to prevent oxidative damage in the lens. More research will be needed in order to confirm the relative importance of of the different roles of vitamin C in the eye lens.

Prevention of intracellular oxidative stress to lens by pyruvate and its ester

Pyruvate is a well-known scavenger of hydrogen peroxide (H2O2). In addition, it scavenges superoxide radical (O2.-). However, evidence on its intracellular antioxidant function is meager at present. Hence, we have examined the effectiveness of this metabolite and its ethyl ester against intracellular oxidative damage to the lens under organ culture. Menadione, a redoxcycling quinone, was used to generate the reactive oxygen species (ROS). It was found to inhibit lens metabolism as evidenced by a decrease of ATP. Additionally, tissue oxidation was apparent by loss of glutathione (GSH), and increase in the level of oxidized glutathione (GSSG), coupled with increase of the urea soluble proteins (water insoluble). The overall physiological damage was apparent by the inhibition of the Na+-K+-ATPase dependent cation pump, as evidenced by a decreased rubidium transport. These deleterious effects were attenuated by pyruvate and ethyl-pyruvate. The later was found to be more effective.

Activity of ubiquitin-dependent pathway in response to oxidative stress. Ubiquitin-activating enzyme is transiently up-regulated

Relations between the ubiquitin pathway and cellular stress have been noted, but data regarding responses of the ubiquitin pathway to oxidative stress are scanty. This paper documents the response of this pathway to oxidative stress in lens cells. A brief exposure of lens epithelial cells to physiologically relevant levels of H2O2 induces a transient increase in activity of the ubiquitin-dependent pathway. Ubiquitin conjugation activity was maximal and increased 3. 5-9.2-fold over the activity noted in untreated cells by 4 h after removal of H2O2. By 24 h after removal of H2O2, ubiquitin conjugation activity returned to the level noted in untreated cells. In parallel to the changes in ubiquitin conjugation activity, the activity of ubiquitin-activating enzyme (E1), as determined by thiol ester formation, increased 2-6.7-fold during recovery from oxidation. Addition of exogenous E1 resulted in an increase in ubiquitin conjugation activity and in the levels of ubiquitin carrier protein (E2)-ubiquitin thiol esters in both the untreated cells and the H2O2-treated cells. These data suggest that E1 is the rate-limiting enzyme in the ubiquitin conjugation process and that the increases in ubiquitin conjugation activity which are induced upon recovery from oxidation are primarily due to increased E1 activity. The oxidation- and recovery-induced up-regulation of E1 activity is primarily due to post-synthetic events. Substrate availability and up-regulation of E2 activities also appear to be related to the enhancement in ubiquitinylation upon recovery from oxidative stress. The oxidation-induced increases in ubiquitin conjugation activity were associated with an increase in intracellular proteolysis, suggesting that the transient increase in ubiquitinylation noted upon recovery from oxidative stress may play a role in removal of damaged proteins from the cells.

Determinations of some trace and heavy metals in rat lenses after tobacco smoke exposure and their relationships to lens injury

Cigarette smoking has been implicated in the pathogenesis of cataract, but the pathogenic mechanism by which cigarette smoke causes cataract is yet to be completely understood. There has been suggestion that oxidative damage caused by accumulation of Fenton reagents (iron and copper) in the lens can cause lens damage and possibly cataract. To investigate the accuracy of this theory the study was planned. A number of twenty-four male Wistar rats were divided randomly into experimental and control groups. The experimental group of rats were exposed to cigarette smoke for two hours in each day over sixty consecutive days and the controls were treated in identical fashion but only exposed to room air. At the end of the study period, both eyes of all the animals were enucleated and one eye prepared for histopathological examination and the other used for the measurement of metal levels. The lenses of experimental animals showed significantly decreased zinc and increased iron, and calcium concentration relative to those of sham exposed controls. However, no significant difference was found in the copper contents of the lenses of both groups. Distinct histopathological changes such as hyperplasia, hypertrophia, and multilayering of epithelial cells and elevations of calcium concentration detected in the lenses of experimental group animals suggested that the lens damage was a result of in-vivo exposure to tobacco smoke. We propose that increased metal contents in the lens can cause lens damage by the mechanism of oxidative stress through formation of oxygen radicals via metal catalysed Fenton reaction.

Cataractogenesis and lipid peroxidation in newborn rats treated with buthionine sulfoximine: preventive actions of melatonin

The purpose of this study was to examine the influence of exogenously administered melatonin on cataract formation and lipid peroxidation in newborn rats treated with buthionine sulfoximine (BSO), a drug which inhibits the rate-limiting enzyme in glutathione (GSH) synthesis, gamma-glutamylcysteine synthase, thereby depleting animals of their stores of the important intracellular antioxidant, GSH. BSO (3 mmol/kg BW) was given for three consecutive days beginning on postnatal day 2; melatonin (4 mg/kg) was injected daily beginning on postnatal day 2 and continuing until the animals were killed (either day 9 or day 17 after birth). None of the control animals (rats treated with neither BSO nor with melatonin) developed lenticular opacification during the observation period. In the BSO-treated rats, 16 of 18 animals (89%) had observable cataracts when they were examined. In rats that received both BSO and melatonin, the incidence of cataracts was highly significantly decreased, i.e., only 3 of 18 rats (7%) had observable cataracts. In addition to cataracts, the level of lipid peroxidation products (malondialdehyde (MDA) and 4-hydroxyalkenals (4-HDA)) was examined in the lens, brain, liver, lung, and kidney of control and experimental animals. In BSO-treated rats, the lens, kidney, and lung exhibited increased levels of MDA plus 4-HDA relative to those measured in the control rats; these increases were reversed in the BSO-treated rats who were injected with melatonin daily. While BSO administration did not increase basal levels of MDA plus 4-HDA in either the brain or liver, melatonin reduced levels of lipid peroxidation products below those measured in the control rats (at 17 days after birth). The changes induced by melatonin are consistent with the free-radical scavenging and antioxidative properties of this indole.

Eales' disease: accumulation of reactive oxygen intermediates and lipid peroxides and decrease of antioxidants causing inflammation, neovascularization and retinal damage

PURPOSE

To measure the blood levels of oxygen and lipid-free radicals as lipid peroxidation products and of vitamins E, C and A, in order to explain intraocular inflammation, retinal neovascularization and detachment in Eales' disease.

METHODS

Levels of the lipid peroxidation products produced by oxygen and lipid free radicals (estimated as thiobarbituric acid reactive substances-TBARS), vitamin E with ferric chloride, vitamin C with 2,6-dichlorophenol-indophenol and vitamin A with antimony trichloride were all evaluated in three groups of subjects between 20 and 40 years of age. Twenty three were patients with Eales' disease in the active perivasculitis stage (Group I), 19 were patients with Eales' disease in the healed-perivasculitis stage (Group II), and 46 were healthy volunteers (Group III), used as normal controls. Patients in each group were subdivided into two age groups, 20-30 and 31-40 years, each group containing both sexes.

RESULTS

The results showed a 4.6- and 5.6-fold increase in the levels of TBARS in erythrocytes of patients with Eales' disease in the active perivasculitis stage (Group I) and a 2-fold increase in patients with Eales' disease in the healed perivasculitis stage (Group II), when compared to levels in the controls (Group III). On the other hand, there was a decrease of 75 and 76.2% in the levels of vitamin E in serum, 34 and 40.9% of vitamin C in plasma and 72.8 and 67% of vitamin A in serum in patients with Eales' disease in the active perivasculitis stage (Group I), as compared to the controls (Group III). Also decreases of 56 and 43.5% of vitamin E in serum, 26.8 and 12.5% of vitamin C in plasma and 50.5 and 49.4% of vitamin A in serum were found in patients with Eales' disease in the healed perivasculitis stage (Group II) as compared to the healthy controls (Group III). The two values of variations between the patients and the normal control group given above for TBARS, vitamins E,C and A are for the two age groups, 20-30 and 31-40 respectively. The differences were statistically significant (P < 0.01 to 0.001).

CONCLUSIONS

Lowered levels of antioxidant vitamins E and C and consequent accumulation of oxygen and lipid free radicals, or vice versa, could explain the inflammation, neovascularization and retinal pathology in patients with Eales' disease. Also, vitamin A deficiency could aggravate retinal illness.

Degradation of hyaluronic acid by photosensitized riboflavin in vitro. Modulation of the effect by transition metals, radical quenchers, and metal chelators

The effect of photoexcited riboflavin (RF) on the viscosity of hyaluronic acid (HA) solutions has been investigated. UV irradiation of RF causes under aerobic conditions fragmentation of HA and a decrease in the viscosity of its solutions. A decrease of HA viscosity occurs in PO(4)-buffered solutions and is accelerated by high pH, Fe2+ (but much less so by Fe3+), certain metal chelators, and horseradish peroxidase (HRP); it is partially inhibited by catalase and less so by superoxide dismutase (SOD). The reactivity of the system was completely blocked by Tris, ethanol, aspirin, d-manitol, dimethylthiourea (DMTU), dimethylsulfoxide (DMSO), and sodium azide. These results indicate that the most likely chemical species involved in the reaction is the hydroxyl radical. Singlet oxygen ((1)O(2)) generation is suggested by the ability of NaN3 and DMSO to completely inhibit the reactivity of the system. These two agents, however, may also interact with OH. radical, as well and suppress the reactivity of the system. H(2)O(2) and O(2).- seem also to be produced in significant amounts, because catalase and SOD partially block the reactivity of the system. The effect of HRP may be due to hydrogen subtraction from HA and H(2)O(2) reduction to water. Photoexcitation of RF may potentially occur in vitro and in vivo in the organs and tissues that are permeable to light, such as the eye or skin, and damage HA and other cell-matrix components causing inflammation and accelerating aging.

Crosslinking of aminophospholipids in cellular membranes of lens by oxidative stress in vitro

We have previously demonstrated by TLC an additional phospholipid spot between phosphatidylethanolamine (PE) and phosphatidylserine (PS) in human cataract. This was further identified as a fluorescent Schiff-base conjugate resulting from crosslinking of reactive carbonyl groups of malondialdehyde (MDA) with the primary amino groups of membrane phospholipids. Evidence presented here shows that such an adduct could be formed in rabbit lens subjected to oxidative stress in vitro. TLC analysis of a lipid extract of a crude membrane fraction obtained from the lens homogenate incubated with 1 mM H2O2, tert-butyl hydroperoxide (TBHP) or MDA for 1-6 h at 25 degrees C, showed that the oxidants and MDA produced time-dependent crosslinking of aminophospholipids. Under identical conditions of incubation with TBHP or MDA, development of the Schiff-base lipid fluorochrome in lens with peak emission at 470 nm when excited at 360 nm also showed a time-dependent increase. The PE.MDA.PS produced in cellular membranes of the lenses cultured for 3 h in Krebs-Ringer medium was 151 nmol/mumol PE, and addition of 1 mM H2O2, TBHP or MDA, increased it to 881, 610 and 375 nmol/mumol PE, respectively. Adduct was also formed when authentic samples of PE and PS were reacted with pure MDA. From the results it is clear that oxidants viz., H2O2 and TBHP, or MDA were effective in promoting crosslinking of lens membrane aminophospholipids by Schiff-base conjugation of primary amino groups with the carbonyl groups of the aldehyde, a breakdown product of lipid peroxides.

Age-related macular degeneration after extracapsular cataract extraction with intraocular lens implantation

PURPOSE

To evaluate the course of age-related maculopathy after cataract surgery.

METHODS

Included were 47 patients with bilateral, symmetric, early age-related macular degeneration (AMD), documented by fluorescein angiography, who underwent extracapsular cataract extraction with intraocular lens implantation in one eye. The fellow eye served as the control. The patients were retrospectively reviewed or prospectively followed.

RESULTS

Wet AMD developed in nine eyes (19.1%) that were treated with surgery compared with two fellow eyes (4.3%). It was detected within 3 months of surgery in four (44.4%) of the nine affected eyes and within 6 to 12 months of surgery in four other eyes (44.4%). Progression to wet AMD occurred significantly more often in men than in women (P < 0.05). Soft drusen were found as a significant ocular risk factor (P < 0.05). The final visual outcome was poor in all eyes with such progression.

CONCLUSIONS

In this study, progression of AMD occurred more often in the surgical eyes compared with the fellow eyes. However, the reasons for the progression of AMD after cataract surgery are still uncertain. Further prospective studies are needed to investigate this observation.

Modelling cortical cataractogenesis. XVIII. In vitro diabetic cataract reduction by venoruton. A flavonoid which prevents lens opacification

The effect of a novel flavonoid, venoruton (a mixture of mono-, di-, tri- and tetrahydroxyethylrutosides) has been investigated in healthy rat lenses and compared with diabetic cataract modelled in vitro. One mM venoruton was added to medium simulating healthy and diabetic conditions for the incubated lenses; damage was followed by either stereoscopic photography of the lenses under a Cooperative Cataract Research Group operating microscope or with our recently developed method: the leakage of lactate dehydrogenase (LDH) into the lens culture media. The increased LDH activity in the medium and observable development of the opacity were correlated with cell damage, which has been found to be associated with globular degeneration and cataract formation. The extent of opacification and LDH release is reduced if 1 mM venoruton is included in the medium. The protective effect may be related to antioxidant activity against reactive oxygen species: decreased luminol luminescence was shown after venoruton addition to either superoxide-generating hypoxanthine plus xanthine oxidase, or hydrogen peroxide.

Quantitation of the reactive oxygen species generated by the UVA irradiation of ascorbic acid-glycated lens proteins

The oxidation products of ascorbic acid rapidly glycate proteins and produce protein-bound, advanced glycation endproducts. These endproducts can absorb UVA light and cause the photolytic oxidation of proteins (Ortwerth, Linetsky and Olesen, Photochem. Photobiol. 62, 454-463, 1995), which is mediated by the formation of reactive oxygen species. A dialyzed preparation of calf lens proteins, which had been incubated for 4 weeks with 20 mM ascorbic acid in air, was irradiated for 1 h with 200 mW/cm2 of absorbed UVA light (gamma > 338 nm), and the concentration of individual oxygen free radicals was measured. Superoxide anion attained a level of 76 microM as determined by the superoxide dismutase (SOD)-dependent increase in hydrogen peroxide formation and of 52 microM by the SOD-inhibitable reduction of cytochrome c. Hydrogen peroxide formation increased linearly to 81 microM after 1 h. Neither superoxide anion nor hydrogen peroxide, however, could account for the UVA photolysis of Trp and His seen in this system. Singlet oxygen levels approached 1.0 mM as measured by the oxidation of histidine, which was consistent with singlet oxygen measurements by the bleaching of N,N-dimethyl-4-nitrosoaniline. High concentrations of sodium azide, a known singlet oxygen quencher, inhibited the photolytic destruction of both His and Trp. Little or no protein damage could be ascribed to hydroxyl radical based upon quenching experiments with added mannitol. Therefore, superoxide anion and H2O2 were generated by the UVA irradiation of ascorbate advanced glycation endproducts, however, the major reactive oxygen species formed was singlet oxygen.

Failure to withstand oxidative stress induced by phospholipid hydroperoxides as a possible cause of the lens opacities in systemic diseases and ageing

Lipid peroxidation (LPO) is a causative factor of cataract. The increased concentrations of primary molecular LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products, were detected in the lipid moieties of the aqueous humor samples obtained from patients with senile and complicated cataracts as compared to normal donors. The degrees of lens clouding were assessed quantitatively by measuring the optical density indices and areas of equidensities using digital image analysis. Human cataractous lenses showed decreased activity of glutathione peroxidase (GPX, catalyzing reduction of organic hydroperoxides including hydroperoxides of lipids). The apparent Km for tert-butylhydroperoxide was 0.434 mM for human normal and cataractous lens GPX. When lenses were exposed for 1 h at 37 degrees C to linoleic acid hydroperoxide (LOOH, 0.5 mM) or egg phosphatidyl-choline hydroperoxide (PLOOH, 1 micro mol per 112 micro mol of phospholipid) in liposomes suspended in the incubation medium, normal, immature and mature human cataractous lenses showed a significant loss in the residual content of liberated LOOH to 62%, 38% or 17%, correspondingly, but little or no reduction was observed with PLOOH in liposomal membranes. Human, rabbit or mice transparent or immature cataractous lenses induced significantly more absorbance changes in conjugated diene, iodometric and TBA-reactive substance measurements when incubated with liposomal membranes which were decreased in the presence of free radical scavengers and antioxidant enzymes (EDTA, SOD, L-carnosine, chelated iron, catalase). Injection into the vitreous body of the rabbit eye of a suspension of liposomes prepared from phospholipids containing LPO products induced the development of posterior subcapsular cataract. Saturated liposomes did not cause clouding of the lens. This modelling of cataract was accompanied by accumulation of fluorescing LPO products in the vitreous body, aqueous humor and the lens and also by a fall in the concentration of GSH in the lens. The peroxidative damage to the lens cell membranes and biomolecules induced in the lack of reductive detoxification of phospholipid hydroperoxides is proposed as the triggering mechanism of cataractogenesis.

Antioxidants and age-related eye disease. Current and future perspectives

Oxidative mechanisms may play an important role in the pathogenesis of age-related eye disease, in particular cataract and macular degeneration, the two most important causes of visual impairment in older adults. For this reason, there is considerable interest in determining whether vitamins and trace minerals with antioxidant properties can be of benefit in preventing the onset or progression of disabling eye disease. Basic research studies have shown that antioxidants can protect against the cumulative effects of oxidative stress in animal models of cataract and macular degeneration. Data from observational epidemiological studies in humans, however, are inconclusive. While results from several studies, primarily cross-sectional and case-control, are compatible with a possible protective role for micronutrients in disease development, data for specific nutrients or specific disease types have often been inconsistent. Further, these observational studies are limited because of the inherent imprecision of dietary exposure data and the likely effects of uncontrolled confounding. Thus, reliable data regarding a potentially important benefit of vitamin supplementation in eye disease will emerge mainly from well-designed, large-scale, randomized trials.

The Nambour study of ocular disease. I. Design, study population and methodology

In association with a study of actinic skin disease, we undertook a comprehensive survey of ocular disease in a population sample of the town of Nambour, Queensland, Australia. Particular emphasis was placed on those diseases with a putative relationship to exposure to solar radiation. In addition to collecting prevalence data, a randomized controlled trial was commenced to determine, among other things, if daily ingestion of 30 mg of beta-carotene supplements reduces the incidence or progression of ocular diseases possibly related to solar radiation exposure. The study design, population and methodology of the study are described in detail as a background to the future reporting of the results. The study should provide unique epidemiological information about eye disease in an Australian community setting due to the representative nature of the subjects and the comprehensive examination performed.

Levels of superoxide dismutase mRNA in rat lens: effect of aging

Superoxide dismutase, the enzyme catalyzing the dismutation of O2.- to H2O2 is known to be present in various ocular and nonocular tissues. In this communication we have determined the gene expression of this enzyme in rat lenses. The investigations have been conducted as a function of age using RNase protection assay. These in vitro assays for the corresponding mRNA suggested that the transcription of the gene is age variant, increasing as a function of age. The levels were significantly lower in the young lenses in comparison to the older lenses.

Vitamin C reduces cytochalasin D cataractogenesis

The effect of cytochalasin D (CD), an actin monomer-stabilizer, has been studied on cataract development in rat lenses. Cataractogenesis was induced by incubating the rat lenses in medium 199 (M199) containing 10(-5) M CD; by the end of 24 h, lenses first developed a visible opacity. The increased lactate dehydrogenase (LDH) activity in the culture medium, leakage of lens cytosolic proteins into the culture medium and observable development of opacity through a dissection microscope were correlated with cell damage associated with cataract formation. Non-denaturing polyacrylamide gel electrophoresis was used to separate three lens LDH isoenzymes. The effect of 1 mM vitamin C (VC) in reducing LDH leakage was also examined. The protective effect of VC on CD-initiated cataractous lenses is significant. This suggest that a portion of the opacity and lens damage may involve oxidative damage to the membrane-cytoskeleton complex which is started by CD, but partially prevented by VC

[Antioxidative vitamins and cataracts in the elderly]

Senile cataract indicates the opacity of ocular lenses occurring in old and especially in very old people. Lens proteins are extremely long-living and often show oxidative damages. Aging and smoking appear to be the greatest risk factors for the development of lens opacities. The sufficient antioxidant protection of young lenses decreases with the aging process. Consequently, the importance of other protective factors increases. Nutritional factors, particularly vitamins with antioxidant properties, may influence the development of senile cataracts in the ocular lens. Meanwhile an association between the supply with vitamin C, E and beta-carotene and the risk of cataract development was demonstrated in animal studies and also in an increasing number of epidemiological studies. These epidemiological studies mainly support the hypothesis that higher vitamin intakes reduce the risk of developing cataracts in old age. The antioxidant properties of the named nutrients give a plausible explanation for the mechanism of cataractogenesis. On the basis of the present data definitive recommendation, necessary for cataract prevention can not yet be established. Some results seem to support higher recommendations. At the moment several large human intervention trials are carried out. Form these studies a further confirmation of the antioxidant hypothesis and of a dose-response-relationship are expected.

Epidemiology of risk factors for age-related cataract

Epidemiologic studies on risk factors for cataract have progressed significantly over the last decade. Age-related cataract is a multifactorial disease, and different risk factors seem to play a role for different cataract types. Cortical and posterior subcapsular cataracts appear to be most closely related to environmental stresses such as ultraviolet exposure, diabetes, and drug ingestion. Nuclear cataracts appear to be associated with smoking. Alcohol use seems to be associated with all cataract types. Consistent evidence also suggests that the prevalence of all cataract types is lower among those with higher education. Most of the current data support a role for antioxidants associated with decreased rates of all cataract types, but further studies are needed. More data are needed to establish the association, if any, of diarrhea, blood pressure, and use of allopurinol and phenothiazines with senile cataracts.

Prevention of cataracts by nutritional and metabolic antioxidants

Among aging disabilities, the one associated with the progressive decline of vision is functionally most disadvantageous. Cataracts are one of the more common causes of such visual disability. Several predisposing factors have been identified in the genesis of this disease. While it is perhaps a multifactorial process, significant developments have taken place in recent years suggesting that oxygen radicals are involved in the development of this aging manifestation. Antioxidant enzymes, such as catalase and superoxide dismutase, have been demonstrated to protect the lens cell membrane from oxidative stress as reflected by the prevention of the Na(+)-K(+)-ATPase-dependent pump deterioration due to oxyradical-dependent oxidation of its proteins and lipids. From the nutritional point of view, antioxidants such as ascorbate and vitamin E also offer significant protection to the lens against damage due to oxidative stress. Evidence regarding the protective effect of these nutrients has been based on lens organ culture studies in the presence of active oxygen, generated photochemically as well as enzymatically. The experiment involving photochemical environs simulate the status of the eye during the photopic vision. In vivo, the effectiveness of ascorbate against cataracts has been tested in rat pups developing cataracts under the oxidative influence of sodium selenite. Certain antioxidants produced metabolically also may be useful in protecting against cataracts. Pyruvate produced in glucose metabolism seems to be an important antioxidant. The efficacy of this compound has been tested within in vitro organ culture as well as in vivo, the latter experiments being done with selenite-treated rats. There is a hope that these and other nutritional and metabolic antioxidants may one day be useful in delaying or even preventing cataract formation in human beings.

Sunlight and cortical cataract

We undertook a prospective clinical study to test our initial impression that cortical opacities are seldom present in the upper part of the lens. Data analysis revealed that of 174 eyes having cortical opacities, only 15 (8.62%) had opacities in the area of the lens between the 10- and 2-o'clock positions. Lid retraction, defined as upper lid position at or above the limbus, was seen in 13 (88.66%) of these eyes. Our study indicates that in the absence of lid retraction, cortical opacities are very rarely seen in the upper segment of the lens, a segment that is normally covered by the upper lid. This suggests a protective effect of the upper lid against cortical opacities, and indirectly it supports the theory that senile cortical opacities may be the result of thermal damage to the lens.

Membrane damage in UV-irradiated lenses

The purpose of this study was to investigate three possible causes of membrane damage following UV irradiation: photooxidation of membrane thiol (SH) groups, peroxidation of membrane lipids and inhibited synthesis of membrane proteins. Thiol loss was not observed. Thin-layer chromatography showed a four-fold increase in several primary lipid peroxidation products such as hydroperoxyl lipids in the epithelial membrane preparations isolated from irradiated lenses. The formation of new hydroxyl lipid bands not seen in control preparations was also observed in isolated membranes from irradiated lenses. Irradiation in the presence or absence of oxygen produced lipid peroxidation products. Aerobic irradiation produced small, but statistically significant increases in lipid hydroxyls and hydroperoxyls relative to controls. Repair of initial damage might be compromised by the observed 60% reduction in rate of protein synthesis measured in lens membranes following irradiation. Synthesis was affected by means other than depleted potassium or elevated calcium levels.

Relation between lens opacities and vitamin and mineral supplement use

PURPOSE

The authors evaluated the cross-sectional and longitudinal relations between lens opacities and intake of vitamins and minerals in supplements.

METHODS

Type and quantity of vitamins and minerals taken currently and 10 years before interview were obtained in a population-based sample of persons in the Nutritional Factors in Eye Disease Study (n = 2152).

RESULTS

In persons without diabetes, regular use of multivitamin preparations 10 years in the past was associated with decreased risk for nuclear sclerosis (odds ratio [OR], 0.6; 95% confidence interval [CI], 0.5, 0.8) and increased the risk for cortical opacities (OR, 1.6; CI, 1.1, 2.2). In persons with diabetes, past multivitamin use was not associated with nuclear sclerosis (OR, 1.1; CI, 0.4,2.7) but with decreased risk for cortical opacities (OR, 0.1; CI, 0.0, 0.9). Cross-sectional associations with current intake of supplements were weaker, but in the same direction. Multivitamin use was not cross-sectionally or longitudinally related to posterior subcapsular cataract in persons with or without diabetes.

CONCLUSION

Use of vitamin supplements is longitudinally associated with nuclear and cortical opacities. However, the direction of the association is influenced by the type of opacity and diabetes status.

DNA single strand breaks in human lens epithelial cells from patients with cataract

In recent years, there has been renewed interest in the association between DNA damage to the lens epithelium and the development of lens opacities. Although a number of in vitro studies have indicated that lens epithelial cells are susceptible to a variety of DNA damaging insults and that these cells possess the capacity to repair such damage, no previous studies have directly addressed whether DNA damage is associated with human cataract in vivo. Utilizing samples of lens epithelial cells obtained from patients undergoing cataract surgery, the percentage of cells containing DNA single strand breaks was directly determined by the single-cell gel assay (SGA) method. Non-cataractous human Eye Bank lenses of similar ages to the cataractous samples and calf lenses were used as controls. In approximately 50% of the cataractous samples analyzed, the proportion of cells containing DNA single strand breaks was significantly higher than in control lenses. No relationship between age and DNA damage was noted. These findings are consistent with the hypothesis that in some human patients with cataract, DNA damage in the lens epithelial cell population may be related to the development of lens fiber cell opacity.

Cataract: relationship between nutrition and oxidation

Opacification of the lens, or cataract, is causally related to the precipitation of proteins or other constituents upon aging. Proteins in the lens are unusually long lived and are subject to extensive damage, including (photo)oxidation. Accumulation of damaged proteins also appears to be due in part to attenuated activity of some proteolytic pathways, which in younger tissue may serve to identify and remove such moieties. The damaged proteins accumulate, aggregate, and precipitate. Compared with other health problems, surgery to remove cataract and related visits to physicians consume the largest proportion of the Medicare budget, i.e., $3.2 billion annually in the United States. The situation is exacerbated in many parts of the world where there is a dearth of ophthalmologists to perform the required number of procedures. Historically efforts to delay cataract assumed a low profile in ophthalmologic research. Recent data, however, indicate that consuming elevated levels of antioxidants such as ascorbate, carotenoids, and tocopherol is associated with delayed development of various forms of cataract. The same beneficial relationship to vision pertains to plasma antioxidant status and to fruit and vegetable intake. Thus, it seems that assuring optimal antioxidant intake can extend lens function. It has been estimated that in the United States over half of the cataract extractions and associated costs would be obviated if cataract could be delayed by 10 years. The data reviewed indicate that optimizing nutrition will help achieve that objective.

Antioxidant activity of plasma from subjects with and without senile cataract

The relationship between overall plasma antioxidant activity and senile cataract was examined in 148 subjects aged 37-90 years. Antioxidant activity of plasma from 52 control and 96 patients with senile cataract was determined by a method which measures the capacity of plasma to inhibit auto-oxidation of bovine brain homogenate. In contrast to previous studies which demonstrated a relationship between decreased levels of antioxidant components in blood and the occurrence of lens opacities, the present study does not show any significant difference between subjects with and without senile cataract.

The prevention of cataract caused by oxidative stress in cultured rat lenses. I. H2O2 and photochemically induced cataract

H2O2 stress is shown to produce cataract in cultured rat lenses. The loss of transparency begins in the equatorial region within 24 hours and the entire superficial cortex is opaque by 96 hours. No involvement of the nuclear region is observed. However after an additional 48 hours, the nuclear region becomes opaque. The loss of transparency is accompanied by a large uptake of H2O which occurs gradually over the 96 hour period, complete loss of glyceraldehyde phosphate dehydrogenase (GPD) activity, almost complete loss of non-protein thiol and a slight decrease in protein thiol. Control lenses show no change other than the establishment of a new non-protein thiol base line approximately 60% lower than 0 time levels. The Alcon glutathione peroxidase type mimic, AL-3823A, completely eliminates almost all of the H2O2 induced effects and the lens remains transparent. Utilizing a more severe photochemical model than may be anticipated physiologically with 10 microM riboflavin and exposure to daylight fluorescent lamps, significant concentrations of superoxide and low levels of OH. are produced as well as extraordinarily high concentrations of H2O2 ranging from about 400 to 1000 microM. As with the H2O2 model, opacification begins at the equator but the cataract develops more rapidly, the lens being completely opaque by 68 hours. Hydration, GPD activity, non-protein and protein thiol all decrease more rapidly than in the H2O2 model. AL-3823A prevents loss of transparency until approximately 92 hours and markedly decreases changes in other parameters. At 92 hours, slight loss of transparency is observed. Catalase is somewhat less effective. AL-3823A is shown to also significantly decrease superoxide levels. The marked delay in the onset of changes in lens biochemistry and physiology in the severe photochemical stress model and the maintenance of normal parameters in the H2O2 model in the presence of AL-3823A suggests that such compounds may prevent cataract caused by oxidative stress under physiological conditions.

Neonatal cataract: aetiology, pathogenesis and management

We review the epidemiology, aetiology, pathogenetic mechanisms and clinical management of neonatal cataract. Visual development and the effects of visual deprivation in the infant with congenital cataract are discussed and related to the timing of surgery. Surgical techniques and the important operative and post-operative complications are discussed. We review post-operative management and compare the different techniques available for aphakic correction, and describe the VEP changes found in patients with monocular cataract.