Effect of vitamin E on glutathione content in red blood cells, aqueous humor and lens of humans and other species

Biochemical Changes in Anterior Chamber of the Eye in Diabetic Patients-A Review

This article aims to provide a comprehensive review of the biochemical changes observed in the anterior chamber of the eye in diabetic patients. The increased levels of inflammatory markers, alterations in antioxidant defense mechanisms, and elevated levels of advanced glycation end products (AGEs) in the aqueous humor (AH) are explored. Additionally, the impact of these biochemical changes on diabetic retinopathy progression, increased intraocular pressure, and cataract formation is discussed. Furthermore, the diagnostic and therapeutic implications of these findings are presented. This study explores potential biomarkers for detecting diabetic eye disease at an early stage and monitoring its progression. An investigation of the targeting of inflammatory and angiogenic pathways as a potential treatment approach and the role of antioxidant agents in managing these biochemical changes is performed.

Corneal UV Protective Effects of a Topical Antioxidant Formulation: A Pilot Study on In Vivo Rabbits

This study aimed to evaluate the protective effect of a topical antioxidant and ultraviolet (UV) shielding action formulation containing riboflavin and D-α-tocopherol polyethylene glycol succinate (TPGS) vitamin E against corneal UV-induced damage in vivo rabbit eyes. In vivo experiments were performed using male albino rabbits, which were divided into four groups. The control group (CG) did not receive any UV irradiation; the first group (IG) was irradiated with a UV-B−UV-A lamp for 30 min; the second (G30) and third (G60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with one drop of the antioxidant and shielding formulation every 15 min, starting one hour before irradiation, until the end of UV exposure. The cornea of the IG group showed irregular thickening, detachment of residual fragments of the Descemet membrane, stromal fluid swelling with consequent collagen fiber disorganization and disruption, and inflammation. The cornea of the G30 group showed edema, a mild thickening of the Descemet membrane without fibrillar collagen disruption and focal discoloration, or inflammation. In the G60 group, the cornea showed a more severe thickening, a more abundant fluid accumulation underneath the Descemet membrane with focal detachment, and no signs of severe tissue alterations, as were recorded in the IG group. Our results demonstrate that topical application of eye drops containing riboflavin and TPGS vitamin E counteracts UV corneal injury in exposed rabbits.

A Novel Vitamin E TPGS-Based Formulation Enhances Chlorhexidine Bioavailability in Corneal Layers

Keratitis is a severe condition characterized by inflammation of the cornea following a local trauma. The most common ocular disease is the bacterial one, which requires an antibiotic treatment. The major limitation of this therapy is the resistance of the antibiotic. For this reason, alternative procedures have been developed and consist of antimicrobial molecules. One of the most used is the chlorhexidine gluconate, which has shown activity versus Gram-positive and Gram-negative bacteria and fungi. In addition to its efficiency, chlorhexidine shows low toxicity levels for mammalian cells and is a low-cost molecule. Despite its multiple benefits, chlorhexidine, if used at concentrations higher than 0.02% (w/w), can cause local eye irritation. Additionally, its poor penetrability through the cornea makes necessary frequent instillation of eye drops for a prolonged time. Due to these limitations, alternative drug delivery strategies are required. Here, we report a novel formulation based on the combination of d-alpha-tocopherol polyethylene glycol 1000 succinate with chlorhexidine, which results in higher accumulation of the drug in human corneas measured by liquid chromatography and strong antimicrobial activity. Moreover, this formulation does not cause any toxic effect on human cells and is well tolerated by rabbit eyes. Therefore this novel formulation represents a good candidate for the treatment of keratitis that overcomes the risk of antibiotic resistance.

Effects of an antioxidant protective topical formulation on retinal tissue of UV-exposed rabbits

PURPOSE

The aim of this study has been to evaluate the protective effect of a topical antioxidant formulation containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine against UV-B-induced damage in in vivo rabbit retina.

METHODS

Twenty male albino rabbits were used. Animals were divided into four groups of five animals each. Control group did not receive any UV irradiation. The first group (IG) was irradiated with a UV-A lamp for 30 min; the second (IG30) and the third (IG60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with 1 drop (approximately 50 µl) of the antioxidant formulation, every 15 min, starting 1 h before irradiation, until the end of the UC exposure.

RESULTS

The retina of IG group showed extensive destruction of the retinal pigment epithelium (RPE) and of the cones and rods layer. The retina of G30 group showed a lesser destruction of both RPE and cones and rods layer. In the G60 group, retina showed an irregular thickening of the RPE, with massive edema of the inner and outer layer immediately adjacent together with a significant reduction of the photoreceptor number.

CONCLUSION

Our results demonstrate that a topical application of eye drops containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine counteracts UV retinal injury in exposed retina rabbits.

Evaluation of antioxidant therapy in experimental Chagas disease

INTRODUCTION:

Stimulation of inflammatory mediators such as cytokines and chemokines may cause oxidative stress in Chagas disease. In this study, we evaluated the merit of vitamins C and E as antioxidant therapy to minimize the oxidative stress-induced damage in an experimental model of Chagas disease.

METHODS:

Ninety-six Swiss mice were infected with Trypanosoma cruzi QM2 and treated with vitamins C, E, or both (C/E) for 60 and 120 days, and their effects compared to placebo administration were evaluated in the acute and chronic disease phases.

RESULTS:

There was no difference in parasitemia among treatment groups. However, histological analysis showed more severe inflammation in the skeletal muscle in the vitamin supplementation groups at both the acute and chronic phases. Biochemical analyses during the acute phase showed increased ferric-reducing ability of plasma (FRAP) and glutathione (GSH) levels in the vitamin C and C/E groups. In the chronic phase, a decrease in GSH levels was observed in the vitamin E group and a decrease in thiobarbituric acid reactive substances (TBARS) was observed in the vitamin C/E group. Moreover, there was a decrease in TBARS in the cardiac tissues of the vitamin C and C/E groups compared to that of the placebo group, although this level was greater in the vitamin E group than in the vitamin C group.

CONCLUSIONS:

The antioxidant action of vitamins C and E reduced oxidative stress in both the acute and chronic phases of Chagas disease, with a marked effect from joint administration, indicating their inherent synergism.

Lutein attenuates oxidative stress markers and ameliorates glucose homeostasis through polyol pathway in heart and kidney of STZ-induced hyperglycemic rat model

PURPOSE

Lutein's role on chronic hyperglycemia-induced oxidative stress and associated glucose homeostasis in heart and kidney is limited. Purpose of the study is to investigate the effect of lutein on cardiac and renal polyol pathway enzymes and oxidative stress markers under hyperglycemia-induced oxidative stress condition using streptozotocin (STZ)-injected rat model.

METHODS

STZ-induced hyperglycemic (fasting blood glucose ≥11 mM) male Wistar rats were divided into two groups (n = 11/group). Group 1 received micellar lutein (39 nmol/day/rat) and group 2 (negative control) received micelle without lutein for 8 weeks. A separate group (no STZ injected) served as a positive control (n = 11/group). Oral glucose tolerance test (OGTT), biweekly urine glucose and activities of aldose reductase (AR) and sorbitol dehydrogenase (SDH) enzymes were assessed. Activities of antioxidant enzymes and antioxidant level were also evaluated.

RESULTS

Lutein-administered hyperglycemic rats showed better glucose tolerance as evidenced with OGTT and biweekly urine glucose when compared to negative control. Activities of AR and SDH were decreased in heart and kidney of lutein-fed hyperglycemic rats. Also, they had significantly (p < 0.05) decreased malondialdehyde levels (66, 34, and 33 %) and increased reduced glutathione level (81, 18 and 92 %) in serum, heart and kidney, respectively. Altered antioxidant enzyme activities such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione transferase were also affected in serum, heart and kidney of lutein-fed diabetic group.

CONCLUSION

Lutein prevented cardiac and renal injury in STZ-induced hyperglycemic rats due to potential amelioration of altered activities in polyol pathway and oxidative stress markers.

Effect of quercetin, genistein and kaempferol on glutathione and glutathione-redox cycle enzymes in 3T3-L1 preadipocytes

CONTEXT AND OBJECTIVE

Many studies have shown that cellular redox potential is largely determined by glutathione (GSH), which accounts for more than 90% of cellular nonprotein thiols. The aim of this study was to delineate the effect of three flavonoids - namely, quercetin, kaempferol and genistein - and exogenous GSH on oxidative damage by the Fenton's pathway through the GSH and GSH-redox cycle enzymes in 3T3-L1 cells.

MATERIALS AND METHODS

3T3-L1 preadipocytes were exposed to each flavonoid and GSH at concentrations of 0, 5, 10, 15, 20 and 25 µM and then GSH levels and activities of glutathione peroxidase (GSH-Px), glutathione reductase (GSH-Rx) and superoxide dismutase (SOD) were measured.

RESULTS

Exogenous GSH did not have significant effect on intracellular GSH although slight decrease was observed at 15-25 µM doses. However, each of the three flavonoids sustained intracellular GSH levels in the cells as compared to the respective controls. Quercetin had the most profound effect, followed by kaempferol and genistein in that order. GSH-Px, GSH-Rx and SOD activities increased for all the doses tested compared to their respective controls. Again, quercetin had the maximum increase in enzyme activities followed by kaempferol and genistein for the enzymes tested.

DISCUSSION AND CONCLUSION

These findings suggest that the flavonoids play an important role in diminishing oxidation-induced biochemical damages. The enhancement of these enzymes may increase the resistance of the organism against oxidative damage by the Fenton's pathway.

Vitamin E and risk of age-related cataract: a meta-analysis

Objective

We conducted a meta-analysis to evaluate the relationship between vitamin E and age-related cataract (ARC).

Design

The fixed- or random-effect model was selected based on heterogeneity. Meta-regression was used to explore potential sources of between-study heterogeneity. Publication bias was evaluated using Begg’s test. The dose–response relationship was assessed by a restricted cubic spline model.

Setting

Relevant studies were identified by a search of PubMed and the Cochrane Library to May 2014, without language restrictions.

Subjects

Studies involved samples of people of all ages.

Results

Dietary vitamin E intake, dietary and supplemental vitamin E intake, and high serum tocopherol levels were significantly associated with decreased risk of ARC, the pooled relative risk was 0·73 (95 % CI 0·58, 0·92), 0·86 (95 % CI 0·75, 0·99) and 0·77 (95 % CI 0·66, 0·91), respectively. Supplemental vitamin E intake was non-significantly associated with ARC risk (relative risk=0·92; 95 % CI 0·78, 1·07). The findings from dose–response analysis showed evidence of a non-linear association between dietary vitamin E intake and ARC. The risk of ARC decreased with dietary vitamin E intake from 7 mg/d (relative risk=0·94; 95 % CI 0·90, 0·97).

Conclusions

The findings of the meta-analysis indicated that dietary vitamin E intake, dietary and supplemental vitamin E intake, and high level of serum tocopherol might be significantly associated with reduced ARC risk.

Oxidative stress markers in aqueous humor of glaucoma patients

PURPOSE

Oxidative stress and antioxidant status in eye tissues may be associated with glaucomatous damage. The aim of this study was to establish the antioxidant status of aqueous humor of patients with primary open-angle glaucoma. For this purpose the authors measured the total reactive antioxidant potential (TRAP) and the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase, and glutathione peroxidase.

DESIGN

Case control study.

METHODS

Aqueous humor was obtained at the time of surgery from 24 patients with glaucoma and 24 cataract patients; TRAP was measured by chemiluminescence. Activities of the antioxidant enzymes were measured spectrophotometrically. Superoxide dismutase activity was determined by inhibition of the rate of adrenochrome formation at 480 nm. Catalase activity was evaluated by decrease of H(2)O(2) absorbance at 240 nm. Glutathione peroxidase (GPx) activity was determined following nicotinamide adenine dinucleotide phosphate oxidation at 340 nm.

RESULTS

Total reactive antioxidant potential value of the cataract group was 124 +/- 5 micromol/l Trolox. This value was significantly decreased, by 64%, in glaucoma patients. An increase of 57% in SOD activity was observed in glaucoma patients when compared with cataract patients (41.7 +/- 2.7 U SOD/ml). Glutathione activity was threefold higher in glaucoma patients than in the cataract group (6.1 +/- 0.6 U/ml). No significant changes were found in catalase levels.

CONCLUSIONS

Oxidative stress may lead to an induction of antioxidant enzymes and contribute to TRAP decrease. Superoxide dismutase, GPx activities, and TRAP may be useful oxidative stress markers in aqueous humor of glaucoma patients.

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.

Complementary and alternative medicine for glaucoma

Given the recent interest in complementary and alternative medicine (CAM), some patients may seek such treatments to supplement their traditional glaucoma management. The prevalence of CAM use for glaucoma is approximately 5%. We reviewed the literature to determine the potential benefit of various alternative treatments. Aside from a temporary osmotic effect from high dose intravenous ascorbic acid, there is no evidence that megavitamin supplementation has a beneficial effect on glaucoma. During exercise, autoregulation in healthy eyes seems to maintain a consistent blood flow rate to the optic nerve despite fluctuations in intraocular pressure (IOP). In a glaucomatous eye, the very modest IOP-lowering that follows exercise may be offset by the initial elevation in IOP that occurs when one first initiates exercise. At this time, there is no evidence to encourage or discourage the use of special diets, acupuncture, relaxation techniques, or therapeutic touch specifically for the treatment of glaucoma. Very little research has been done on the majority of herbal remedies with regard to their treatment of glaucoma. Marijuana can cause a profound lowering of IOP, but the high nonresponse rate, short half life, and significant toxicity are strong indicators that it is not an appropriate therapeutic agent. Ginkgo biloba and some other Chinese herbal remedies do not affect IOP, but may improve blood flow to the optic nerve and, as such, may have a beneficial effect on glaucoma. These agents have recognized toxicities. Although there are some well-designed studies of alternative treatments, many of the recommendations for using alternative treatments are currently unsupported by the data provided.

Effect of smoking on lipid profile, lipid peroxidation and antioxidant status in normal subjects and in patients during and after acute myocardial infarction

We studied changes in lipid peroxidation, vitamin E status and lipid profile due to smoking in healthy subjects, patients with acute myocardial infarction (MI), and in stabilized patients surviving MI. A significant increase in malondialdehyde (MDA) concentrations was observed in MI patients, more than in smokers (P<0.05), as compared to control. The plasma vitamin E as well as the ratio of vitamin E/lipids were significantly lower in MI patients as compared to stable ischemic heart disease (IHD) patients and controls. Our data show that smoking is associated with lowered antioxidant status in MI.

Effect of oral supplementation with vitamin E on the oxido-reductive status of red blood cells in normal mice and mice subject to oxidative stress by chronic administration of adriamycin

The effect of oral vitamin E supplementation on the oxido-reductive status of red blood cells in normal mice and those subject to oxidative stress by chronic administration of the anti-tumour drug Adriamycin was investigated. Mice were randomly separated into three groups of 20 animals each and maintained on diets identical in all respects except for vitamin E content. Group 1 received a low vitamin E diet that provided 10 mg vitamin E/kg body weight/day, group 2 received a normal mice chow diet (45 mg vitamin E/kg body weight/day) while group 3 received a high vitamin E diet (200 mg vitamin E/kg body weight/day). In comparison with the normal mice in group 1, their counterparts in groups 2 and 3 exhibited significantly higher (P < 0.001) activities of superoxide dismutase (SOD) in red blood cells (79.4% higher in group 2 and 114.2% higher in group 3, respectively) and produced lower concentrations of malondialdehyde (MDA) (22.9% less in group 2 and 51.2% less in group 3, respectively), with little difference in the glutathione peroxidase (GPX) activity. In Adriamycin-treated animals on the low vitamin E diet (group 1) the red blood cell SOD activity and MDA production were 46.2% and 200.7% higher (P < 0.001), respectively, and the GPX activity was 39.1% lower than in the red blood cells of untreated (normal) animals in the same group. The Adriamycin-induced changes were significantly less in animals receiving higher doses of vitamin E (groups 2 and 3). Thus, in the group maintained on the high vitamin E diet (group 3), Adriamycin administration resulted in only a 38.9% increase in the MDA production above that generated by red blood cells of normal mice in the same group, with no significant change in the SOD or GPX activities. Thus, in normal conditions as well as in conditions of oxidative stress, high doses of vitamin E appear to be able to protect the oxido-reductive status of red blood cells by modulating the extent of lipid peroxidation as well as the activities of antioxidant enzymes.

Nutrition supplements and the eye

PURPOSE

A review of the role of vitamins, minerals, carotenoids and essential fatty acids in relation to eye health. The mode of action may be directly on the eye or by promoting bodily health on which the eye depends.

RESULTS

The lens and retina suffer oxidative damage and the anti-oxidant vitamins A, C and E are implicated as protective. Studies in man give indifferent support to the role of nutrition in the development of cataract. In the elderly, vitamin intake may be inadequate, so that a vitamin supplement may be reasonable. Zinc has a role in retinal metabolism and may be beneficial in macular degeneration. Selenium has an anti-oxidant role. Other minerals including copper have a less defined role. Carotenoids are concentrated at the macula and have an anti-oxidant role. A reduced risk of macular degeneration is found in relation to a high serum level. The essential fatty acid, gamma-linolenic acid (GLA), is useful in Sjögren's syndrome and may help in other dry eye conditions. Omega-3 fatty acids are important in retinal development and have a role in preventing cardiovascular disease.

CONCLUSION

All persons should be encouraged to maintain healthy nutrition. Middle-aged and elderly patients may benefit from a supplement. An intake in excess of the recommended daily intake may be beneficial, but this is not proven. Further clinical trials are indicated to define the advisability of vitamin, mineral and other supplements. Dosages for recommended intake and for supplements are given.

Improved myeloperoxidase assay for quantitation of neutrophil influx in a rat model of endotoxin-induced uveitis

Previously described models of endotoxin-induced uveitis quantify neutrophil influx into the eye using biochemical or direct cell count methods that result in an underestimation of ocular leukocyte accumulation following the inflammatory stimulus. We have optimized the rat model of endotoxin-induced uveitis by first overcoming interference in the biochemical assay of myeloperoxidase due to endogenous ocular reductants and cellular constituents containing free thiol functional groups. This was accomplished by simultaneously 1) extensively diluting soluble, interfering substances and 2) blocking tissue sulfhydril functional groups during tissue homogenization. Uveitis was induced in rats by subplantar injection of endotoxin. Twenty-four hours later, eyes were enucleated, homogenized, fractionated, and myeloperoxidase activity of neutrophils sedimenting with the membranous pellet was extracted. Previously published extraction procedures yielded only 40% of total assayable myeloperoxidase activity. Optimal recovery of myeloperoxidase activity (>twofold increase) was achieved only with two sequential extractions using 50 mM phosphate buffer (pH 7.4) containing 10 mM N-ethylmaleimide, and subsequent solubilization of myeloperoxidase activity by extraction with 0.5% hexadecyltrimethylammonium bromide in 50 mM phosphate buffer (pH 6.0). This modified extraction procedure and optimized myeloperoxidase assay conditions (300 microM hydrogen peroxide and 1.5 mM o-dianisidine) were then used to enhance the uveitis model. Maximum ocular neutrophil accumulation was observed at endotoxin doses of 100-200 microg. Total ocular neutrophil infiltrations ranged from 250,000 to 800,000 cells/globe. This leukocyte influx was inhibited dose-dependently by topical ocular administration of dexamethasone, with half-maximal inhibition observed at a concentration of 0.01%, w/v. Further validated by the correlation of biochemical results with histological evaluation, the refined methodology described in this report has application in assessing the ophthalmic therapeutic potential of antiinflammatory agents.

Extracellular glutathione peroxidase and ascorbic acid in aqueous humor and serum of patients operated on for cataract

Patients operated on for cataract (32 men/75 women, aged 50-93 years) were studied with respect to antioxidative agents in aqueous humor and serum. Extracellular glutathione peroxidase (eGSHPx) was demonstrated in aqueous humor for the first time by a radioimmunoassay, the concentration of eGSHPx being 0.66(0.18) mg/l (mean(S.D.)). The concentration of eGSHPx in serum was 3.81(0.84) mg/l, and its level in aqueous humor was 18(7)% of that level. Serum selenium had positive correlations with both serum eGSHPx (r = 0.34, P < 0.001) and aqueous humor eGSHPx (r = 0.25, P = 0.011). However, there was no relation between the concentrations of eGSHPx in aqueous humor and in serum, suggesting that the maintenance of eGSHPx levels in the two fluids is controlled by different mechanisms beside selenium status. There was an inverse correlation between age and serum eGSHPx but not with aqueous humor eGSHPx. The concentration of ascorbic acid in aqueous humor was 2.04(0.58) mmol/l, and it was closely correlated to the level of ascorbic acid in serum (0.052(0.032) mmol/l), r = 0.58 (P < 0.001). The ratio between the level of ascorbic acid in aqueous humor and that in serum was 39(17). There was no significant difference among patients with nuclear (n = 39), cortical (n = 20), posterior-subcapsular (n = 23) or mixed (n = 23) lens opacity with respect to levels of eGSHPx and ascorbic acid in serum and aqueous humor. Since serum ascorbic acid is related to ascorbic acid intake, its association to aqueous humor ascorbic acid indicates that dietary habits are important for maintaining that level which could play an important role in protecting ocular tissue against oxidative damage. The role of eGSHPx secreted into aqueous humor in the oxidant defence system needs further study.

Arf 193nm excimer laser corneal surgery and photo-oxidation stress in aqueous humor and lens of rabbit: one-month follow-up

Twenty male albino rabbits were studied. Four animals served as controls; the remaining 16 animals represented the treated group. All the treated animals were exposed to the same amount of energy delivered by the excimer laser (pulse rate: 20 Hz, fluence 250mJ/cm2; number of pulses: 6032; cumulative UV dose 1508 J/cm2) and were divided into eight groups of 2 animals each (four eyes). Samples of aqueous humor and lens were obtained at the following intervals: 5, 10, 20 and 40 min and 1, 2, 3 and 4 weeks after photorefractive keratectomy (PRK). The levels of reduced and oxidized glutathione, hydrogen peroxide, ascorbic acid and malondialdehyde were determined. Aqueous humor analyses, twenty min after PRK, showed no significant differences with pre-treatment values, while the observed variations in lens were constantly present over the entire follow-up period (one month). These findings suggest that the biochemical lens alterations induced by PRK may represent the earliest events relevant to cataractogenesis in the rabbit.

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.

Pharmacological treatment strategies in age-related cataracts

Cataract is the major cause of blindness worldwide and at present the only approved treatment in many countries including the UK and USA is surgical removal of the lens. In other countries various anti-cataract drugs are available without proof of their efficacy. Research is continuing into the possible benefits of several groups of drugs and some vitamins. The first to be studied were sorbitol-lowering agents (aldose reductase inhibitors) based on the sorbitol hypothesis for diabetic cataract. Sorbitol-lowering agents have distinct effects in vitro and many of them delay the development of cataract in galactose-fed rats. A few delay cataract in diabetic rats but none have been proved effective in clinical trials, although these continue. Aspirin, paracetamol (acetaminophen) and ibuprofen delay diabetic cataract in rats, and have been shown to delay other experimental cataracts. Case-control studies from 3 continents indicate that these drugs, or at least aspirin, protect against cataract. Results of studies on all 3 drugs indicate a benefit even at low doses. Population-based studies did not identify any protection against early lens opacities but tiny opacities that do not impair vision are not a problem. Bendazac protects lens proteins in vitro and delays cataractogenesis in x-irradiated rats. In humans, it reached the clinical trial stage but most trials have been small and with subjective criteria of opacification. One objectively monitored trial suffered from a high drop-out rate. Other preparations studied less extensively include vitamins, aminoguanidine to prevent protein cross-linking in diabetes and agents designed to boost glutathione levels. It is probable that some agents which may delay or prevent cataract will be proved effective soon, and in the end there may be different drugs to delay cataract in different high risk groups. This is what might be expected of a multifactorial disease, although compounds that intervene in the final common pathways to cataract could have a broad efficacy.

Effect of photooxidation on the eye lens and role of nutrients in delaying cataract

The function of the eye lens is to collect and focus light on the retina. To do so, it must remain clear during the decades of life. Upon aging, lens constituents are damaged and precipitate in opacities called senile cataracts. Laboratory and epidemiologic data indicate that the damage is due in part to light and active forms of oxygen. Antioxidant nutrients - ascorbate, carotenoids, and tocopherol - appear to offer protection against cataract. Fifty million persons worldwide are blind due to cataract, and, in the U.S., there are 1.2 million cataract surgeries performed at an annual cost (including physician visits) of over $3.2 billion. It has been estimated that a 10-year delay in the development of cataract would eliminate the need for half the surgeries. Since it will not be possible to replace most of the damaged lenses, it is essential to determine the efficacy of supplying adequate levels of antioxidant nutrients early in life to preserve lens function.

Effects of dietary supplementation with vitamin E, riboflavin and selenium on central nervous system oxygen toxicity

We attempted to modify the resistance of rats to hyperbaric oxygen (HBO)-induced central nervous system (CNS) toxicity, by increasing the tissue antioxidant potential through dietary factors. Groups of rats were fed excesses of vitamin E (VIT E) alone or in combinations with riboflavin (RIB), selenium (Se) or both, for 30 days. A control group was maintained on an unsupplemented diet. On the 23rd day animals to be exposed were implanted with chronic electrodes for electrocorticographic (ECoG) recording. Later, each group was divided into two subgroups, of which one was exposed to 4.5 atmospheres absolute (ATA) of 100% oxygen (O2) for 30 min., hereafter referred to as "exposed", noting the time of appearance of first electrical discharge (FED) in their ECoG. The remaining subgroups were left unexposed. Forty-eight hours later, all animals were sacrificed and some of their tissues were analyzed for glutathione (GSH). The GSH level in the liver, brain, lungs and blood of all experimental subgroups were significantly higher than in the control unexposed counterparts. Combinations of RIB and/or Se with VIT E failed to show a greater increase in GSH over VIT E alone. This increase was, however, not accompanied by a meaningful delay in the appearance of FED. Forty-eight hours post-exposure, the brain GSH levels of all exposed subgroups were still lower than the respective pre-exposure levels. Yet, in the treated exposed subgroups the GSH levels observed 48 hr after exposure were already higher than in the untreated unexposed controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic human diseases as oxidative risk factors in cataractogenesis. II. Chronic renal failure

In this study we have investigated the oxidative metabolism of red cells (RBC), plasma, serum and aqueous humour of healthy subjects and of age-matched cataractous patients with and without chronic renal failure (CRF). Reduced glutathione (GSH) levels in RBC were lower in CRF patients than in the other groups. Oxidized glutathione (GSSG) plasma levels in CRF patients were higher than those of controls and cataractous subjects. The activity of the enzyme glucose-6-phosphate dehydrogenase in RBC was significantly reduced in CRF patients with respect to the other two groups. The levels of malondialdehyde (MDA) in RBC and in lens were about twice in CRF patients compared with the other two groups. The plasma levels of vitamin E were diminished in CRF patients; on the contrary, the biological liquid oxidant activity (BLOA) of serum in CRF patients was significantly higher than in controls and in cataractous patients without CRF. Cataractous patients with and without CRF showed similar levels of GSH in aqueous humour; on the contrary, the content of GSSG was significantly higher in CRF patients. Our findings seem to demonstrate that CRF patients are exposed to oxidative stresses that could probably act synergistically with uraemia and carbamylation of lens proteins. This synergism could explain why CRF represents a relatively high risk factor for cataract.

Cell calcium, vitamin E, and the thiol redox system in cytotoxicity

The controversial role of extracellular Ca2+ in toxicity to in vitro hepatocyte systems is reviewed. Recent reports demonstrate that extracellular Ca2+-related cytotoxicity is dependent on Ca2+-influenced vitamin E (alpha-tocopherol) content of isolated hepatocytes. Based on a Ca2+-omission model of in vitro oxidative stress, the role of vitamin E in cytotoxicity is further explored. This model demonstrates the interdependence of the GSH redox system and vitamin E as protective agents during oxidative stress. Following chemical oxidant-induced depletion of intracellular GSH, cell morphology and viability are maintained by the continuous presence of cellular alpha-tocopherol above a threshold level of 0.6-1.0 nmol/10(6) cells. alpha-Tocopherol threshold-dependent cell viability is directly correlated with the prevention of the loss of cellular protein thiols in the absence of intracellular GSH. Potential mechanisms for this phenomenon are explored and include a direct reductive action of alpha-tocopherol on protein thiyl radicals, and the prevention of oxidation of protein thiols by scavenging of lipid peroxyl radicals by alpha-tocopherol. It is suggested that in light of the threshold phenomenon of vitamin E prevention of potentially severe oxidative stress-induced cytotoxicity, its use as a protective agent against an oxidative challenge in vivo should be reassessed.