Photoinduction of cataracts in rat lens in vitro. Preventive effect of pyruvate

Intact rat lenses were incubated in riboflavin-containing Tyrode solution or medium-199, generating photochemically active species of oxygen and the oxidative stress measured in terms of the decrease in active accumulation of rubidium, and the fall in the levels of glutathione and ATP. Addition of pyruvate to the medium prevented the tissue against oxidative damage as evidenced by a greater accumulation of rubidium and higher levels of glutathione and ATP. Pyruvate was thus found to be effective against the toxicity of oxygen derivatives, particularly the hydrogen peroxide. In dark experiments also, conducted in glucose-free medium, the uptake of rubidium was substantially greater in the presence of pyruvate. The levels of ATP were also higher. These results, therefore, suggest that this ketoacid is beneficial to the tissue through its ability to decompose H2O2 as well through providing a metabolic support. The development of in vitro cataract under the photochemical effects of riboflavin and oxygen was also effectively thwarted by pyruvate. The results are thus potentially useful from the point of view of developing pyruvate and similar compounds as effective anticataract agents.     

Attenuation and delay of diabetic cataracts by antioxidants: effectiveness of pyruvate after onset of cataract

Cataract is one of the most significant vision-impairing complications of diabetes. The present study examined the feasibility of inhibiting cataract formation by treatment with pyruvate, a metabolite known to effectively scavenge reactive species of oxygen and inhibit protein glycation, both known to be involved in the genesis of diabetic cataracts. In addition, pyruvate stimulates tissue metabolism, which is depressed with the onset of cataract formation. The objective of our experiments was to determine if this compound could be effective in offsetting the progress of cataract, specifically if administered after the diabetes-induced lens changes have begun, as opposed to the previous reports wherein it has been reported to delay cataract formation if administered prophylactically with the immediate onset of diabetes. Diabetes was induced by intraperitoneal administration of streptozotocin to mice. Lens transparency was assessed by slit lamp examination and its photography. ATP was determined enzymatically by reacting it with luciferin-luciferase mixture and measuring the fluorescence intensity. The findings described herein are in accordance with this possibility. The incidence of cataract in the group of diabetic animals, where treatment with pyruvate was initiated after the initial lens changes set in, was significantly lower at all times of observation in comparison to the untreated diabetic group. In addition, the severity of opacities in the pyruvate-treated group, when present, was much minor, the transparency of these cases being close to that in the control animals. The ophthalmic findings are supported biochemically by ATP levels, which were significantly higher in the pyruvate group in comparison to the untreated group. The present findings emphasize the clinical usefulness of initiating treatment with anti-oxidants and metabolic agonists even when the lens changes are detected at the time of the diabetes diagnosis. The latter usually comes much later than the onset of visual aberrations. Prophylaxis is not an absolute requirement.     

Nutrition and the prevention of cataracts

PURPOSE OF REVIEW: Oxidative stress is a major cause of cataract development. Numerous studies have been published regarding the effects of nutritional supplementation on cataract progression. RECENT FINDINGS: Basic science research has demonstrated a protective effect of antioxidants on lens tissue, and supplementation with vitamin C and lutein/zeaxanthin has been associated with a decreased risk of cataract formation in multiple observational studies. One large interventional trial demonstrated a significant difference in participants treated with high-dose vitamin C versus placebo, but a more recent interventional study did not replicate these findings. In a review of the carotenoids lutein and zeaxanthin, the Food and Drug Administration concluded there is insufficient evidence to suggest that supplementation with these carotenoids lowers the risk of cataract formation. While high doses of multivitamins, antioxidants, or lutein and zeaxanthin are unlikely to be of significant ophthalmic benefit to the general public, these nutrients may help individuals exposed to high oxidative stress, such as heavy smokers, and those with poor nutrition. SUMMARY: Supplementation with vitamin C, lutein, zeaxanthin, or a multivitamin may help certain populations, but is unlikely to affect the progression of cataracts in most patients.     

氨基胍滴眼液防治大鼠糖尿病性白内障的研究

目的探讨氨基胍对链脲佐菌素诱导的大鼠糖尿病性白内障的防治效果及其作用机制。方法采用一次性腹腔内注射链脲佐菌素(65mg·kg-1)的方法建立大鼠糖尿病模型,血糖值大于14mmol·L-1为成模标准。治疗组左眼滴氨基胍溶液,2次·d-1。每周监测大鼠血糖、尿糖、体重的变化,并在裂隙灯下观察大鼠晶状体混浊的进展。第13周测定晶状体中谷胱甘肽还原酶活力、过氧化氢酶、谷胱甘肽以及糖化蛋白的含量。结果71%(32/45)达成模标准,并出现糖尿病表现。糖尿病大鼠晶状体混浊呈2阶段发展,前8周缓慢进展及后5周快速进展。氨基胍眼液治疗可延缓糖尿病性白内障发生,第4周出现统计学差异(P<0.05)。氨基胍治疗组晶状体中糖基化蛋白含量明显低于未治疗组(P<0.05),氨基胍治疗组晶状体中谷胱甘肽含量较未治疗组有提高。结论氨基胍滴眼液可抑制早期糖尿病性白内障的进展,其抗糖基化蛋白作用可能参与抑制糖尿病性白内障的形成。     

Modeling cortical cataractogenesis. V. Steroid cataracts induced by solumedrol partially prevented by vitamin E in vitro

Rat lenses incubated in tissue culture medium (M 199) maintain their transparency for a long period of time. The soluble corticosteroid, solumedrol (methyl prednisolone sodium succinate) was added to the medium, at concentrations including the range expected during rejection episodes following organ transplantation (3.8 X 10(-9) M-3.8 X 10(-6) M). At the lowest level used (3.8 X 10(-9) M), five lenses of 12 became opaque following a 48 hr incubation, while at higher concentrations of solumedrol almost all lenses developed opacities. Addition of vitamin E to the medium resulted in partial prevention of the cataract as judged by the smaller proportion of lenses becoming opaque. Examination of the lenses by scanning and transmission electron microscopy (SEM and TEM, respectively), indicated that in untreated lenses the initial location of the cataract is at the anterior pole of the lens where a deepening area of degeneration formed, followed by a uniform subcapsular layer of degeneration spreading over the remainder of the lens. Damage at this location is not typical of most in vitro cortical cataracts. In the presence of vitamin E the extent of damage was less, involving, initially, an equatorial wedge of globular degeneration and spreading anteriorly and posteriorly in a thinner subcapsular layer. This type of damage was more typical of that seen previously for cataracts induced by cytochalasin D, elevated glucose and hygromycin B.     

Aldose reductase inhibitors and prevention of galactose cataracts in rats

Our previous studies have shown that the aldose reductase inhibitor (ARI), sorbinil, prevents galactose-induced alterations and cataracts in rat lenses. We have now used sorbinil as well as another ARI, Eisai compound E-0722, to determine their potency in inhibiting aldose reductase- and galactose-induced alterations in lens morphology and Na+-K+-ATPase activity. Young Sprague Dawley rats were fed Purina Rat Chow plus 50% galactose, with or without 15 mg sorbinil, 0.15, 0.5 or 1.0 mg of E-0722/kg body weight per day. Controls were given Purina Rat Chow with or without ARIs. Lenses were studied for up to 60 days following the initiation of the diet using morphological, cytochemical and biochemical approaches to assess any alterations in the lens. While galactose-induced damage and cataracts were delayed by low doses (0.15 mg and 0.5 mg) of E-0722, they were completely prevented by the administration of 15 mg of sorbinil or 1 mg of E-0722/kg body weight per day. This study further showed that just 1 mg of E-0722 was more effective in preventing cataracts than 15 mg sorbinil. Thus it appeared that E-0722 was a more potent inhibitor of aldose reductase than sorbinil.     

Antioxidants in prevention of cataracts in South India: methodology and baseline data*

PURPOSE: To describe the methodology and baseline data for the Antioxidants in Prevention of Cataracts (APC) study in South India. METHODS: The APC study is a prospective, 5-year, randomized, triple-masked, placebo-controlled, field-based clinical trial to examine the effect of antioxidants (combination tablet of vitamins A, C, and E) on progression of cataract. The primary outcome variable is cataract progression (nuclear opalescence), evaluated with the slit-lamp biomicroscope by the Lens Opacification Classification System III method. Secondary outcome variables are progression in cortical and posterior subcapsular opacity and nuclear color, change in best corrected visual acuity, myopic shift, and treatment failure (progression to cataract surgery or best corrected vision worse than 20/400 in an eye). Inclusion criteria are age between 35 and 50 years and best-corrected visual acuity of 20/40 or better. Exclusion criteria are a diagnosis of diabetes mellitus or nonfasting blood glucose level>7.8 mmol/L, history or presence of various ocular conditions or treatment forms, or current use of vitamin supplements. Baseline ophthalmic, demographic, and potential cataract risk factor data (such as smoking, sunlight, or alcohol exposure) were compared between groups on an intent-to-treat basis. RESULTS: Of 954 people screened, 798 were enrolled, a sample size which exceeded the required estimate. More than 80% of subjects had 20/20 or better vision in at least one eye, and baseline prevalence of significant cataract according to the LOCS III grading scale was high. The two treatment groups were comparable for all baseline measures except alcohol intake. CONCLUSION: The sample size and group baseline characteristics will provide sufficient power to detect a change in cataract progression within 5 years.     

Postinflammatory cataracts in the mouse: induction by human mycoplasma-like organisms.

Cataracts often occur in humans secondary to uveitis. Uveitis may be caused by various infectious agents, but rarely is the agent detected in the cataract. Mycoplasma-like organisms (MLO) were recently reported to cause human uveitis and retinitis. Cataracts were often present in those inflamed eyes. MLO are intracellular cell wall deficient pathogenic bacteria. They are pleomorphic tubulospherical and filamentous organisms with a characteristic ultrastructural appearance. No MLO culture system has been found despite 20 years of effort. The diagnosis of MLO disease rests on detection of the organisms in parasitised cells by a transmission electron microscope and response to antibiotics. In human intraocular inflammatory disease MLO are detectable in parasitised leucocytes and retinal pigment epithelial cells at the disease sites. Inoculation of MLO from a human source into mouse eyelids produced intraocular, chronic, progressive, inflammatory disease, with intraocular leucocytes parasitised by MLO in 15 of 100 mice versus 0 in 200 controls (p less than 0.05). This report describes the cataracts with MLO-parasitised intralenticular leucocytes in the inflamed eyes of 14 of those 15 mice versus 0 in 200 control mice (p less than 0.05). The results indicate that MLO penetrated the lens capsules to produce the cataracts, and they suggest that MLO could cause human cataracts. Alternative methods for detection of MLO and rifampin treatment of MLO intraocular disease are discussed.     

Sugar cataracts in vitro: Implications of oxidative stress and aldose reductase I

The rat lens, when cultured in medium 199 containing 55·5 mm-glucose and 15% fetal calf serum, developed a visible equatorial cortical opacity by the 96th hour. The gerbil lens, whose aldose reductase activity was twice that of the rat lens, developed such an opacity after 24 hr. The development of opacity is thus faster in a lens with higher aldose reductase activity. The relation of aldose reductase with genesis of sugar cataracts is also evident from the observation that substitution of glucose by xylose accelerated cataract formation. Xylose is known to have lower K_m for aldose reductase than glucose. Fortification of the media with vitamin E (2·4 μm) or GSH (0·1 mm) did not prevent the cataract development. The level of lens malonaldehyde, one of the products of lipid peroxidation, was also unaffected either following culture in high sugar media or following in vivo induction of diabetes by streptozotocin. The oxidative stress, thus, does not seem to be involved in initiating the formation of sugar cataracts.     

The effect of L-carnitine in the prevention of ionizing radiation-induced cataracts: a rat model

Background The objective was to determine the antioxidant role of L-carnitine (LC) against ionizing radiation-induced cataracts in lens after total cranium irradiation of rats with a single dose of 5 Gy. Methods Sprague-Dawley rats were used in this experiment and were divided into three groups. Group 1 did not receive LC or irradiation (control group). Group 2 received a 5 Gy gamma irradiation as a single dose to the total cranium (RT group). Group 3 received total cranium irradiation plus 100 mg/kg body weight/day LC (RT+LC group). The rats were irradiated using a cobalt-60 teletherapy unit. At the end of the 10th day, the rats were sacrificed and their eyes were enucleated. The lenticular activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were measured. Furthermore, the lenticular content of an indicator of lipid peroxidation, malondialdehyde (MDA), was measured. Results Irradiation significantly increased the MDA level as an end product of lipid peroxidation. Irradiation also significantly decreased SOD activity and increased GSH-Px activity, indicating the generation of oxidative stress and an early protective response to oxidative damage. Irradiation with 5 Gy to the total cranium as a single fraction formed cataracts in the rat lenses. Cataract development was detectable in 9 rats in the RT group, and in only 4 rats in the RT+LC group 10 days after irradiation. LC administration plus irradiation significantly decreased the MDA level and increased the activity of SOD and GSH-Px enzymes, which might indicate the protection of the lenses from gamma radiation-induced cataracts. Conclusions L-carnitine may protect against the damage produced by gamma radiation by increasing the activity of the SOD enzyme and by scavenging free radicals generated by ionizing radiation. As a result of this process, MDA as an indicator of lipid peroxidation may decrease.     

Classification of hereditary cataracts in children by linkage analysis.

A total of 12-different types of hereditary cataracts have been positively assigned to the gene map. They are located on autosomes as well as on the X chromosome. This establishes several kinds of cataracts as distinct diseases caused by different mutations. In selected cases the information may be helpful for prenatal diagnosis.     

Modelling cortical cataractogenesis: VI. Induction by glucose in vitro or in diabetic rats: Prevention and reversal by glutathione

Cataractogenesis can be induced by glucose in the rat lens in vitro and in vivo. In vitro, this is done by increasing the amount of glucose in the medium surrounding the isolated lens; within 48 hr considerable globular degeneration is seen subcapsularly, deeper in the equatorial region. In vivo, it is achieved by making the rat diabetic by injecting streptozotocin i.v., which selectively destroys the β-cells of the pancreas; the blood serum glucose level increases markedly, and thence the aqueous humour level and, in turn, the lens concentration. Globular degeneration occurs as in vitro, but not until 6 weeks is a degree of damage observed comparable to that seen in the lenses incubated in vitro for only 48 hr. Lenticular sorbitol and fructose are also markedly elevated as a result of the high glucose levels. If glutathione (GSH) is present in the medium (0·1 mm) or injected s.c. daily into the diabetic rats, there is no evidence of subcapsular globular degeneration of the cortical fiber cells, even though the lenticular levels of glucose, sorbitol and fructose are the same as when GSH was not given; this is true for either the in vitro or in vivo situation. although individual values in the two situations do differ somewhat from one another. When rats were given GSH beginning several weeks after the diabetic state had been induced, the damage subsequently observed was much less than if the rats had been diabetic without GSH for the same total length of time; it was also much less than damage which should have occurred by the time GSH treatment was instituted. It would thus appear that a certain amount of reversal of the globular degeneration is possible, although damage in the equatorial region (wedge-shaped) seems less amenable to rescue by glutathione.The data indicate that glutathione can prevent or diminish the severity of sugar cataractogenesis. and that there would appear to be more steps in sugar cataractogenesis than simply osmotic damage, although this may be the primary event.