Antioxidant vitamins in cataract prevention

Synthesis and biological evaluation of chalcone, dihydrochalcone, and 1,3-diarylpropane analogs as anti-inflammatory agents

Twenty-one chalcones were prepared via aldol condensation and subsequent reduction of these compound led to the corresponding dihydrochalcone and 1,3-diphenylpropane derivatives. The synthetic products were examined for their effects on NO inhibition in LPS-activated mouse peritoneal macrophages. Among the tested compounds, a 1,3-diarylpropane analog, 2-(3-(3,4-dimethoxyphenyl)propyl)-5-methoxyphenol (3p), displayed the most significant inhibitory effects against NO production. To investigate the mechanism of action, the effects of 3p on iNOS and COX-2 protein expression were studied by immunoblot. The results concluded that 3p is capable of inhibiting iNOS expression in LPS-induced RAW264.7 cells via attenuation of NF-κB signaling by ERK, p38, and JNK.

Age-related cataract in men in the selenium and vitamin e cancer prevention trial eye endpoints study: a randomized clinical trial

IMPORTANCE

Observational studies suggest a role for dietary nutrients such as vitamin E and selenium in cataract prevention. However, the results of randomized clinical trials of vitamin E supplements and cataract have been disappointing and are not yet available for selenium.

OBJECTIVE

To test whether long-term supplementation with selenium and vitamin E affects the incidence of cataract in a large cohort of men.

DESIGN, SETTING, AND PARTICIPANTS

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) Eye Endpoints Study was an ancillary study of the Southwest Oncology Group-coordinated SELECT, a randomized placebo-controlled 4-arm trial of selenium and vitamin E conducted among 35,533 men, 50 years and older for African American participants and 55 years and older for all other men, at 427 participating sites in the United States, Canada, and Puerto Rico. A total of 11,267 SELECT participants from 128 SELECT sites participated in the SELECT Eye Endpoints ancillary study.

INTERVENTIONS

Individual supplements of selenium (200 μg per day from L-selenomethionine) and vitamin E (400 IU per day of all rac-α-tocopheryl acetate).

MAIN OUTCOMES AND MEASURES

Incident cataract was defined as a lens opacity, age related in origin, and responsible for a reduction in best-corrected visual acuity to 20/30 or worse based on self-reports confirmed by medical record review. Cataract extraction was defined as the surgical removal of an incident cataract.

RESULTS

During a mean (SD) of 5.6 (1.2) years of treatment and follow-up, 389 cases of cataract were documented. There were 185 cataracts in the selenium group and 204 in the no selenium group (hazard ratio, 0.91; 95 % CI, 0.75-1.11; P = .37). For vitamin E, there were 197 cases in the treated group and 192 in the placebo group (hazard ratio, 1.02; 95 % CI, 0.84-1.25; P = .81). Similar results were observed for cataract extraction.

CONCLUSIONS AND RELEVANCE

These data from a large cohort of apparently healthy men indicate that long-term daily supplementation with selenium and/or vitamin E is unlikely to have a large beneficial effect on age-related cataract.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00784225.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effects of multivitamin supplement on cataract and age-related macular degeneration in a randomized trial of male physicians

PURPOSE

To test whether long-term multivitamin supplementation affects the incidence of cataract or age-related macular degeneration (AMD) in a large cohort of men.

DESIGN

Randomized, double-blind, placebo-controlled trial.

PARTICIPANTS

A total of 14,641 US male physicians aged ≥ 50 years.

INTERVENTION

Daily multivitamin or placebo.

MAIN OUTCOME MEASURES

Incident cataract and visually significant AMD responsible for a reduction in best-corrected visual acuity to 20/30 or worse based on self-reports confirmed by medical record review.

RESULTS

During an average of 11.2 years of treatment and follow-up, a total of 1817 cases of cataract and 281 cases of visually significant AMD were confirmed. There were 872 cataracts in the multivitamin group and 945 cataracts in the placebo group (hazard ratio [HR], 0.91; 95% confidence interval [CI], 0.83-0.99; P = 0.04). For visually significant AMD, there were 152 cases in the multivitamin group and 129 cases in the placebo group (HR, 1.19; 95% CI, 0.94-1.50; P = 0.15).

CONCLUSIONS

These randomized trial data from a large cohort of middle-aged and older US male physicians indicate that long-term daily multivitamin use modestly and significantly decreased the risk of cataract but had no significant effect on visually significant AMD.

Ocimum sanctumModulates Selenite-Induced Cataractogenic Changes and Prevents Rat Lens Opacification

PURPOSE

To study the effect of Ocimum sanctum (OS) on selenite-induced morphological and biochemical changes in isolated rat lenses as well as on cataract incidence in rat pups.

METHODS

Transparent rat lenses were divided into normal, selenite-only, and four treated groups. Selenite-only and treated group lenses were subjected to oxidative stress in vitro by incorporating sodium selenite (100 microM) in the culture medium. The effect of OS (70, 140, 280, and 560 microg/ml) was studied on the levels of reduced glutathione (GSH) and thiobarbituric acid reacting substances (TBARS) in selenite-challenged lenses. The lowest concentration of OS offering significant modulation on these two parameters was determined. Subsequently, the effect of prior and cotreatment with the lowest effective concentration of OS was studied on TBARS, GSH, and on lens antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GSHPx), catalase (CAT), and glutathione-S-transferase (GST). Changes in lens protein profiles under different incubation conditions were analyzed by SDS gel-electrophoresis. In vivo, cataract was induced by a single subcutaneous injection of sodium selenite (25 micromole/kg b.w.) to 9-day-old rat pups. The anticataract effect of OS (5 and 10 mg/kg b.w.) injected intraperitoneally 4 hr prior to selenite challenge was evaluated by the presence of lens nuclear opacity in rat pups on the 16th postnatal day. Insolubilization of lens proteins post-selenite injection was monitored for 4 days.

RESULTS

The lenses in the selenite-only group developed cortical opacities in 24 hr. OS showed different degrees of positive modulation in selenite-induced morphological as well as biochemical changes. The lowest effective dose of OS that significantly modulated glutathione and thiobarbituric acid reacting substances was found to be 140 microg/ml. At this dose, a significant increase in antioxidant enzyme levels and preservation of normal lens protein profile was observed. OS at the dose of 70 microg/ml did not show any significant protection with respect to either morphology or biochemistry of lenses. In vivo, 5 and 10 mg/kg of OS reduced the incidence of selenite cataract by 20% and 60%, respectively, and prevented protein insolubilization as well.

CONCLUSIONS

Aqueous extract of OS possesses potential anticataract activity against selenite-induced experimental cataractogenesis. The protective effect was supported by restoration of the antioxidant defense system and inhibition of protein insolubilization of rat lenses as well.

Alcohol consumption and risk of cataract extraction: a prospective cohort study of women

PURPOSE

To investigate the association between alcohol consumption and the risk of cataract extraction.

DESIGN

Population-based prospective cohort study.

PARTICIPANTS

A total of 34,713 women participating in the Swedish Mammography Cohort, age 49 to 83 years, completed in 1997 a self-administered questionnaire about alcohol, smoking, and other lifestyle factors.

METHODS

The women were followed from September 1997 through September 2004. The cohort was matched with registers of cataract extraction from the study area.

MAIN OUTCOME MEASURES

Incident surgical extraction of age-related cataract.

RESULTS

During 84 months of follow-up, we found 3587 incident cases of age-related cataract extraction. Compared with never drinkers, the relative risk of cataract extraction among current drinkers was 1.11 (95% confidence interval [CI] 1.02-1.21) after adjustment for age and other potential risk factors. In multivariate analysis, an increment of 13 g alcohol intake per day (corresponding to 1 drink = 330 ml of beer, 150 ml of wine, or 45 ml of liquor) was associated with a 7% increased risk of cataract extraction (relative risk, 1.07; 95% CI 1.02-1.12). Mean age at cataract extraction among nonsmoking women who used alcohol was 75 years, compared with 77.6 years among never drinkers.

CONCLUSIONS

These prospective data suggest that daily use of >/=1 alcoholic drinks was associated with a modest increase of risk for cataract extraction. The risk increased with increasing alcohol consumption.

Ingestion of IH636 grape seed proanthocyanidin extract to prevent selenite-induced oxidative stress in experimental cataract

PURPOSE

To investigate whether dietary supplementation with IH636 grape seed proanthocyanidin extract (GSPE) prevents selenite-induced cataract.

SETTING

Department of Ophthalmology, Gulhane Military Medical Academy, Ankara, Turkey.

METHODS

Thirty Spraque-Dawley rat litters were put randomly into 3 groups. In group 1 (n = 10), sodium selenite (30 nmol/g body weight) was injected subcutaneously on postpartum day 10. In group 2 (n = 10), sodium selenite (30 nmol/g body weight) was injected on postpartum day 10 and oral GSPE (100 mg/kg body weight) was given for 1 week after sodium selenite injection. Only subcutaneous saline was injected in group 3 (control, n = 10). The development of cataract was assessed for 3 weeks, and its density was graded and photographed with a slitlamp. Removed rat lenses were analyzed for glutathione (GSH) and malondialdehyde (MDA).

RESULTS

All of the rats in group 1 had cataract between stage 6 and stage 3. In group 2, only 5 of 10 eyes had cataract between stage 3 and stage 2 and no cataract occurred in the remaining 5 rats. The difference between mean cataract stages in group 1 and group 2 was significant (P<.05). The mean GSH level in group 1 was significantly lower than in group 2 and controls (P<.05). The mean MDA level in group 1 was significantly higher than in group 2 and controls (P<.05).

CONCLUSIONS

IH636 grape seed proanthocyanidin extract effectively suppressed cataract formation in rats. Routine consumption of grape seed proanthocyanidin extract in the form of food or dietary supplement may offer a prophylactic measure against onset and progression of cataract.

Lycopene attenuates oxidative stress induced experimental cataract development: an in vitro and in vivo study

OBJECTIVES

Lycopene, a nutritional antioxidant, was evaluated for its anticataract potential to further establish its role in cataract prevention.

METHODS

The ability of lycopene to modulate the biochemical parameters was investigated by in vitro studies. Enucleated rat lenses were maintained in organ culture containing Dulbecco's Modified Eagles Medium alone or in addition with 100 microM selenite and served as the normal and control groups, respectively. For the test group, the control medium was supplemented with 10 microM lycopene. The lenses were incubated for 24 h at 37 degrees C. At the end of the incubation period, the lenses were examined for morphologic variation, and biochemical parameters such as reduced glutathione, the lipid peroxidation product malondialdehyde, and the antioxidant enzymes glutathione peroxidase, glutathione S-transferase, superoxide dismutase, and catalase were estimated. In vivo selenite cataract was induced in 9-d-old rats by subcutaneous injection of sodium selenite (25 micromoles/kg of body weight). The rats in the test group were injected with lycopene (200 microg/kg body weight, intraperitoneally) 4 h before the selenite challenge. The incidence of cataract was observed when the rats first opened their eyes. Galactose cataract was induced in rats by feeding 30% galactose in the diet. Rats in the test group were fed orally with 200 microg/kg of lycopene daily, and rats in the control group received only vehicle. Cataract stages were graded at regular intervals.

RESULTS

A fall (25%) in the glutathione level and a rise (32%) in the malondialdehyde content were observed in control as opposed to normal lenses. Lycopene supplementation in the medium significantly (P < 0.001) restored glutathione and malondialdehyde levels. A significant decrease in the activity of antioxidant enzymes also was observed in the control lenses. A significant restoration in the activities of superoxide dismutase (P < 0.05) and catalase and glutathione S-transferase (P < 0.01), with no effect on glutathione peroxidase, was observed in the lycopene-supplemented group. Lycopene also reduced the incidence of selenite cataract. Only 9% of the eyes in the test group developed dense nuclear opacity as opposed to 83% in the control group. A significant delay in the onset and progression of galactose cataract was observed with oral feeding of lycopene. Only 35% of the eyes developed mature cataract as opposed to 100% in the control group.

CONCLUSIONS

Lycopene protects against experimental cataract development by virtue of its antioxidant properties, and it may be useful for prophylaxis or therapy against cataracts.

Design of Physicians' Health Study II--a randomized trial of beta-carotene, vitamins E and C, and multivitamins, in prevention of cancer, cardiovascular disease, and eye disease, and review of results of completed trials

PURPOSE

To assess the balance of benefits and risks of supplementation with beta-carotene, vitamin E, vitamin C, and multivitamins on cancer, cardiovascular (CVD), and eye diseases.

DESIGN

Physicians' Health Study II (PHS II) is a randomized, double-blind, placebo-controlled trial enrolling 15,000 willing and eligible physicians aged 55 years and older. PHS II will utilize a 2 x 2 x 2 x 2 factorial design to test alternate day beta-carotene, alternate day vitamin E, daily vitamin C, and a daily multivitamin, in the prevention of total and prostate cancer, CVD, and the age-related eye diseases, cataract and macular degeneration. PRIOR RESULTS: The final results of the recently completed Physicians' Health Study I (PHS I), a randomized, double-blind, placebo-controlled trial in 22,071 healthy US male physicians, indicated that beta-carotene supplementation (50 mg on alternate days) had no significant benefit or harm on cancer or CVD during more than 12 years of treatment and follow-up. In regards to cancer, there were possible benefits on total and prostate cancer in those with low baseline levels assigned to beta-carotene, a finding compatible with the Chinese Cancer Prevention Study for combined treatment with beta-carotene, vitamin E, and selenium in a poorly nourished population. Further, with respect to CVD, there were apparent benefits of beta-carotene supplementation on subsequent vascular events among a small subgroup of 333 men with prior angina or revascularization. The currently available data from randomized trials of primary prevention are sparse and inconsistent for vitamin E and non-existent for vitamin C and multivitamins. For eye diseases, namely cataract and age-related macular degeneration, there are no completed large-scale randomized trials of antioxidant vitamins.

CONCLUSIONS

PHS II is unique in several respects. PHS II is the only primary prevention trial in apparently healthy men testing the balance of benefits and risks of vitamin E on cancer and CVD. In addition, PHS II is the only primary prevention trial in apparently healthy men to test the balance of benefits and risks of vitamin C, multivitamins, as well as any single antioxidant vitamin, alone and in combination, on cancer, CVD, and eye diseases. Finally, PHS II is the only trial testing a priori the hypotheses that beta-carotene and vitamin E may reduce the risks of prostate cancer. Thus, PHS II will add unique as well as importantly relevant and complementary information to the totality of evidence from other completed and ongoing large-scale randomized trials on the balance of benefits and risks of beta-carotene, vitamin E, vitamin C, and multivitamins alone and in combination on prevention of cancer, CVD and eye diseases.

Antioxidant vitamins and age-related eye disease

Basic research studies suggest that oxidative mechanisms may play an important role in the pathogenesis of cataract and age-related macular degeneration, the two most important causes of visual impairment in older adults. These findings raise the possibility that vitamins and trace minerals with antioxidant properties can be of benefit in preventing the onset or progression of disabling eye disease. Results from observational epidemiological studies in humans, however, are inconclusive. Although findings from several studies, primarily cross-sectional and case-control, are generally compatible with a possible protective role for micronutrients in disease development, the data for specific nutrients or specific disease types are inconsistent. The imprecision of dietary exposure data and the likely effects of uncontrolled confounding further limit these observational studies. Well-designed, large-scale, randomized trials are required to evaluate definitively the potentially important benefit of vitamin supplementation in eye disease.

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.

Long-term supplementation with alpha-tocopherol and beta-carotene and age-related cataract

PURPOSE

To study if long-term supplementation with alpha-tocopherol or beta-carotene is associated with cataract prevalence and severity.

METHODS

An end-of-trial random sample of 1828 participants from the randomized, double-blind, placebo-controlled clinical trial the alpha-tocopherol, beta-carotene cancer prevention study. The alpha-tocopherol, beta-carotene cancer prevention study was originally designed to examine whether supplementation with alpha-tocopherol or beta-carotene would reduce the incidence of lung cancer in male smokers. The participants for this study lived in Helsinki City or Uusimaa province and were at entry to the alpha-tocopherol, beta-carotene cancer prevention study 50 to 69 years old and smoked at least 5 cigarettes per day. They received alpha-tocopherol 50 mg/day, beta-carotene 20 mg/day, a combination of the two, or placebo supplements for 5 to 8 years (median 6.6 years). Outcome measures were: cortical, nuclear, and posterior subcapsular cataract, differentiated and quantified with lens opacity classification system (LOCS II). Lens opacity meter provided a continuous measure of cataract density.

RESULTS

Supplementation with alpha-tocopherol or beta-carotene was not associated with the end-of-trial prevalence of nuclear (odds ratio 1.1 and 1.2, respectively), cortical (odds ratio 1.0 and 1.3, respectively), or posterior subcapsular cataract (odds ratio 1.1 and 1.0, respectively) when adjusted for possible confounders in logistic model. Neither did the median lens opacity meter values differ between the supplementation groups, indicating no effect of alpha-tocopherol or beta-carotene on cataract severity.

CONCLUSION

Supplementation with alpha-tocopherol or beta-carotene for 5 to 8 years does not influence the cataract prevalence among middle-aged, smoking men.

Determination of ascorbic acid in human vitreous humor by high-performance liquid chromatography with UV detection

PURPOSE

Ascorbic acid (AA) accumulates in vitreous at a concentration several times higher than in plasma. It has been suggested that AA may serve as an antioxidant that protects ocular tissues from free radical attack. There are many reports about the concentration of AA in ocular tissues. However, AA in adult human vitreous humor has not been determined. We measured concentrations of AA from pathologic human vitreous samples and compared the results.

METHODS

AA was measured by high-performance liquid chromatography (HPLC) with UV detection. Human vitreous humor was collected from patients undergoing pars plana vitrectomy.

RESULTS

AA was quantified in vitreous humor of proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), macular hole (MH), idiopathic premacular fibrosis (PMF), and Terson syndrome (Terson). The concentrations of AA were 120.9 +/- 36.3 micrograms/ml (mean +/- SD), 129.8 +/- 36.6, 311.5 +/- 126.7, 446.9 +/- 154.2 and 406.0 +/- 22.0, respectively. There was no significant difference between the PDR and the PVR groups (unpaired t-test). Patients with PDR and PVR showed significantly lower concentrations of AA than those with MH, PMF, and Terson (p < 0.01).

CONCLUSIONS

These findings suggest that increased oxidative stress may be produced in the ocular tissues of eyes with PDR and PVR, and AA appears to be consumed (oxidized) in performing its protective role.

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.

[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.

Antioxidants and eye disease

Oxidative mechanisms are believed to 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 epidemiologic 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 cataract and macular degeneration, 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. Such data are already being collected in the National Eye Institute-sponsored Age Related Eye Disease Study, as well as in the Physicians' Health Study and Women's Health Study.

Serum antioxidant vitamins and risk of cataract

OBJECTIVE

To investigate serum concentrations of alpha tocopherol, beta carotene, retinol, and selenium for their prediction of end stage cataract.

DESIGN

A case-control study, nested within a cohort study, based on the linkage of records of subjects aged 40-83 from a health survey with those from the national Finnish hospital discharge register.

SUBJECTS

47 patients admitted to ophthalmological wards for senile cataract over 15 years and two controls per patient individually matched for sex, age, and municipality.

MAIN OUTCOME MEASURE

Concentration of serum micronutrients, development of cataract according to whether operation was performed.

RESULTS

Low serum concentrations of antioxidant vitamins predicted the development of senile cataract, the odds ratio between the lowest third and the two higher thirds of the distribution of serum concentrations of alpha tocopherol and beta carotene being 1.9 (95% confidence interval 0.9 to 4.1) and 1.7 (0.8 to 3.8), respectively. Patients with both alpha tocopherol and beta carotene concentrations in the lowest third had an odds ratio of 2.6 (1.0 to 6.8) of cataract compared with subjects in the top two thirds. The associations were strengthened by adjustment for potential confounding factors such as occupation, smoking, blood pressure, serum cholesterol concentration, body mass index, and diabetes. No association was found between the serum concentrations of selenium, retinol, and retinol binding protein and the risk of cataract.

CONCLUSIONS

Low serum concentrations of the antioxidant vitamins alpha tocopherol and beta carotene are risk factors for end stage senile cataract. Controlled trials of the role of antioxidant vitamins in cataract prevention are therefore warranted.

Levels of reduced pyridine nucleotides and lens photodamage

Since most of the known factors that are associated with cataract formation are oxidative in nature, one would expect that a highly reductive environment might arrest or retard the progress of cataract formation. Reduced nucleotides, both NADH and NADPH, are potent reductants with a large negative redox potential of -320 mV. Lenses of certain species contain high levels of these nucleotides, presumably due to the presence of taxon specific crystallins. We have utilized this situation to investigate whether the levels of reduced pyridine nucleotides modulate photo-oxidative damage to the lens. We have monitored the time dependent loss of tryptophan fluorescence upon photodamage for lenses from guinea pig, rabbit and frog (Rana) that contain high levels of pyridine nucleotides and compared with the lenses from rat, Xenopus and a mutant strain of guinea pig that contain significantly lower amounts of these nucleotides. About 75% and 90% of the initial fluorescence intensity is lost in the case of rat and Xenopus lenses, respectively, after a total of 35 min exposure. Rabbit, guinea pig and frog lenses, under identical conditions, show only about 35-40% loss of the initial fluorescence. It appears that the lenses that contain high levels of reduced nucleotides are less susceptible to photodamage. The observed anti-oxidative role of reduced nucleotides in the lenses indicates the possibility of testing reductants (NADPH, NADH and their functional analogues) as potential candidates to therapeutically intervene in the process of cataractogenesis.

Effect of vitamin C on sorbitol in the lens of guinea-pigs made diabetic with streptozotocin

Marginally vitamin C-deficient guinea-pigs treated with the diabetogenic agent streptozotocin were compared with those liberally supplied with vitamin C, for functional indices of vitamin C status, particularly in the eye lens. Weanling male Dunkin-Hartley guinea-pigs were fed on diets with 0.1 g vitamin C/kg (marginally deficient), or 5 g/kg (liberally supplied), and some received intraperitoneal streptozotocin (two doses of 150 mg/kg body-weight). About half the streptozotocin-treated animals had high urinary glucose following an oral glucose dose; these animals also grew more slowly than the others. At 4 months after streptozotocin the animals were killed for measurement of tissue vitamin C, glucose and sorbitol. Streptozotocin moderately increased the concentration of glucose in plasma, lens and aqueous humour. Lens sorbitol levels increased only in the group exposed to streptozotocin plus marginal vitamin C. There was a significant (P less than 0.02) positive correlation between urinary glucose and lens sorbitol levels overall. Liberal vitamin C intake may thus counteract the effect of streptozotocin diabetes on lens sorbitol, suggesting a new function of vitamin C, possibly related to cataractogenesis and to the biochemical lesions associated with diabetes.

Glutathione and related indices in rat lenses, liver and red cells during riboflavin deficiency and its correction

Biochemical changes in lenses and at other sites in adult rats were investigated during the induction and correction of riboflavin deficiency. Riboflavin deficient (D), 1-day-repleted (R1), 2-days-repleted (R2), 16-days-repleted (R3), food-restricted, weight-matched controls (CFR) and ad libitum-fed controls (CAL) were compared. Activation coefficients of erythrocyte and lens glutathione reductase, which became abnormal in the deficient (D) animals, were corrected to varying extents in the repleted (R) groups. Hepatic flavin concentrations were lowered in the groups with raised glutathione. Inter-group differences in hepatic glutathione concentrations were not simply related to tissue flavin depletion or its reversal, but were complicated by changes in liver: body-weight ratios. Inter-group differences in lenticular glutathione levels were very small. In both liver and lens, sorbitol concentrations were lowest in group R3 and highest in groups D, R1 and R2. Lens ascorbate levels and the lens enzymes, aldose reductase, sorbitol dehydrogenase, glutathione peroxidase and superoxide dismutase, were not significantly affected by diet. Thiobarbituric acid-reactive substances were increased in riboflavin-deficient rat lenses but were lowered in riboflavin-deficient plasma samples. The results suggest overall that while riboflavin deficiency may affect certain biochemical indices, such as sorbitol and thiobarbituric-reactive substances, in the lens and other tissues, these changes are not the result of lowered glutathione levels. They also clearly demonstrate the importance of inanition as a confounding factor in the interpretation of changes resulting from riboflavin deficiency in experimental animals.

Vitamin C: newer insights into its biochemical functions

Ever since the discovery of vitamin C (ascorbic acid), scientists have been intrigued as to how ascorbic acid deficiency can lead to the diverse symptoms exhibited in scurvy. Only in recent years has it been appreciated that ascorbic acid has important functions in many cellular reactions and processes in addition to its role in collagen synthesis. The few such reactions that are understood at the molecular level make it apparent that ascorbic acid does not directly participate in enzyme-catalyzed conversion of substrate to product. Instead, the vitamin regenerates prosthetic metal ions in these enzymes in their required reduced forms. This is in agreement with other antioxidant functions of vitamin C, e.g., scavenging of free radicals. Ascorbate and other antioxidant nutrients are presumed to play a pivotal role in minimizing the damage from oxidative products, including free radicals. This protective function is twofold: the already-oxidized groups in prosthetic centers of enzymes are reduced and the oxidants and free radicals are removed.