Accumulation of lipid peroxidation products in cataractous lenses

A study was made of the content of lipid peroxidation products (LPP) in the lenses extracted during operations for cataract as well as in transparent human lenses. In a mature cataract, the elevated content of primary, secondary and end products of lipid peroxidation (diene and triene conjugates, Schiff bases) was revealed. The content of LPP was identical in different clinical patterns of a mature cataract (senile, traumatic, complicated), which points to the universal role of lipid peroxidation in lenticular opacity.     

Desferal-Mn(III) in the therapy of diquat-induced cataract in rabbit.

In rabbit lenses subjected to oxidative stress, induced by 1 mM diquat in vitro, there were 7- to 10-fold increases (p less than 0.001) in malondialdehyde, conjugated dienes, and carbonyl dienes, indicating extensive peroxidation of cellular membrane lipids, and approximately a 60% decrease in reduced glutathione. In the presence of 0.1-5 mM Desferal-Mn(III) these changes were diminished by 50-70%. In an experimental group of 12 rabbits having diquat-induced cataract, Desferal-Mn(III) (5% w/v) applied topically as a 50-microliters eye drop four times per day and a single intraperitoneal dose of 64 mg/kg body wt daily for 5 weeks (including pretreatment for 1 week) retarded the progression of lens opacities, whereas, in a control group of 6 rabbits treated with the vehicle (0.15 M NaCl) cataract progressed to an advanced grade. Treatment with Desferal-Mn(III) also significantly diminished production of O2.- and OH. in the lens, aqueous humor, and vitreous humor, and of H2O2 in the aqueous humor and vitreous humor. It also suppressed lipid peroxidation and oxidation of protein-SH of the lens and restored lenticular glutathione and ascorbate to normal levels.     

Antioxidative enzyme activity and metabolism of peroxide compounds in the crystalline lens during cataractogenesis

Lens antioxidative enzyme activity (catalase, superoxide dismutase, glutathione peroxidase) in cataract as well as the possibility of cataract induction by the lipid peroxidation products and their influence on the content of reduced thiols (oxy-red balance) were studied. It was shown that the rate of the H2O2 decomposition by the human cataract lenses is lowered in comparison with the normal lenses. This is not due to the lowered catalase or glutathione-peroxidase 1 activity, but depends on the deficiency of reduced glutathione in the lens. Activity of superoxide dismutase and glutathione peroxidase metabolizing organic hydroperoxides is significantly lowered in the cataract lenses. Lipid peroxidation products injected into the rabbit vitreous induce posterior subcapsular cataract, which is accompanied by depletion of reduced glutathione level in the lens. The conclusion is made that two interrelated processes: accumulation of H2O2 and of lipid peroxides induce aggregation of the soluble proteins and the fragmentation of the membrane structures in cataract lenses.     

Lens opacity induced by lipid peroxidation products as a model of cataract associated with retinal disease

The cataractous lenses of patients with retinitis pigmentosa have been studied by electron microscopy. The posterior subcapsular opacities showed common ultrastructural features. Large areas of disruption of the lens fibre pattern were observed which showed an increase in the number of fibre membranes per unit area. In many regions an elaborate and regular folding of membranes was noted which produced complex 'figure-of-eight' and 'tramline' patterns, as well as membranous lamellar bodies. Masses of various size globules were also identified. It has been established that injection into the vitreous body of the rabbit eye of a suspension of liposomes prepared from phospholipids containing lipid peroxidation products induces the development of posterior subcapsular cataract. Such modelling of cataract is based on a type of clouding of the crystalline lens similar to that observed in cataract resulting from diffusion of toxic lipid peroxidation products from the retina to the lens through the vitreous body on degeneration of the photoreceptors. Saturated liposomes (prepared from beta-oleoyl-gamma-palmitoyl-L-alpha-phosphatidylcholine) do not cause clouding of the lens, which demonstrates the peroxide mechanism of the genesis of this form of cataract. Clouding of the lens is accompanied by accumulation of fluorescing lipid peroxidation products in the vitreous body, aqueous humor and the lens and also by a fall in the concentration of reduced glutathione in the lens. From the results it is concluded that lipid peroxidation may initiate the development of cataract.     

Antioxidant activity of L-carnosine, a natural histidine-containing dipeptide in crystalline lens

Lipid peroxidation was shown to be an initiatory cause of cataract development in some cases. It has been established that injection into the vitreous body of the rabbit eye of a suspension of liposomes prepared from phospholipids containing lipid peroxidation products induces the development of posterior subcapsular cataract. Such modelling of cataract is based on a type of clouding of the crystalline lens similar to that observed in cataract resulting from diffusion of toxic lipid peroxidation products from the retina to the lens through the vitreous body on degeneration of the photoreceptors. Saturated liposomes (prepared from dipalmitoylphosphatidylcholine) did not cause clouding of the lens, which demonstrated the peroxide mechanism of the genesis of this form of cataract. Clouding of the lens was accompanied by accumulation of fluorescing lipid peroxidation products in the vitreous body, aqueous humor and the lens and also by a fall in the concentration of reduced glutathione in the lens. The ability of L-carnosine (beta-alanyl-L-histidine) to interact directly with lipid peroxidation products suggested its anticataract properties. The effect of L-carnosine on inhibiting or reversing the formation of cataract induced by the administration of lipid peroxidation products was discovered. This phenomenon appeared to be related with normalization of the peroxide metabolism parameters in the crystalline lens. In view of the data, an aqueous solution of L-carnosine is physiologically acceptable in effective nonsurgical treatment of cataracts.     

Decomposition of H2O2 by human cataractous lenses

It was shown that human lens opacity was accompanied by the decrease in the lens ability to cleave H2O2 (10(-4) M), added to the lens-surrounding medium. The rate of peroxide decomposition at the stage of mature cataract in isolated human lenses was 3.5 times lower than that of the control human lenses (transparent lens, initial cataract). Specific catalase inhibitor--3-amino,IH-1,2,4-triazole showed no significant influence on the rate of H2O2 cleavage. Reduced glutathione (10 microM) added to the lens incubation medium induced a sharp increase in the rate of H2O2 detoxication. The results indicate that reduced glutathione metabolism is of primary importance in the maintenance of anti-peroxide activity in the lens.     

Mitochondria induce oxidative stress, generation of reactive oxygen species and redox state unbalance of the eye lens leading to human cataract formation: disruption of redox lens organization by phospholipid hydroperoxides as a common basis for cataract disease

The aging eye appears to be at considerable risk from oxidative stress. Lipid peroxidation (LPO) is one of the mechanisms of cataractogenesis, initiated by enhanced promotion of oxygen free radicals in the eye fluids and tissues and impaired enzymatic and non-enzymatic antioxidant defenses of the crystalline lens. The present study proposes that mitochondria are one of the major sources of reactive oxygen species (ROS) in mammalian and human lens epithelial cells and that therapies that protect mitochondria in lens epithelial cells from damage and reduce damaging ROS generation may potentially ameliorate the effects of free radical-induced oxidation that occur in aging ocular tissues and in human cataract diseases. It has been found that rather than complete removal of oxidants by the high levels of protective enzyme activities such as superoxide dismutase (SOD), catalase, lipid peroxidases in transparent lenses, the lens conversely, possess a balance between peroxidants and antioxidants in a way that normal lens tends to generate oxidants diffusing from lenticular tissues, shifting the redox status of the lens to become more oxidizing during both morphogenesis and aging. Release of the oxidants (O(2)(-)·, H(2)O(2) , OH·, and lipid hydroperoxides) by the intact lenses in the absence of respiratory inhibitors indicates that these metabolites are normal physiological products inversely related to the lens life-span potential (maturity of cataract) generated through the metal-ion catalyzed redox-coupled pro-oxidant activation of the lens reductants (ascorbic acid, glutathione). The membrane-bound phospholipid (PL) hydroperoxides escape detoxification by the lens enzymatic reduction. The lens cells containing these species would be vulnerable to peroxidative attack which trigger the PL hydroperoxide-dependent chain propagation of LPO and other damages in membrane (lipid and protein alterations). The increased concentrations of primary LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products were detected in the lipid moiety of the aqueous humor samples obtained from patients with cataract as compared to normal donors. Since LPO is clinically important in many of the pathological effects and aging, new therapeutic modalities, such as patented N-acetylcarnosine prodrug lubricant eye drops, should treat the incessant infliction of damage to the lens cells and biomolecules by reactive lipid peroxides and oxygen species and "refashion" the affected lens membranes in the lack of important metabolic detoxification of PL peroxides. Combined in ophthalmic formulations with N-acetylcarnosine, mitochondria-targeted antioxidants are promising to become investigated as a potential tool for treating a number of ROS-related ocular diseases, including human cataracts.     

Hydrogen peroxide in the aqueous humor and cataract formation in human diabetes

Hydrogen peroxide in the aqueous humor was measured in cataractous eyes from normal subjects and in cataractous eyes from diabetic subjects. The level of H2O2 in the aqueous humor was significantly higher in diabetes than in the idiopathic forms. It is likely that in the eye, impaired enzymic defenses lead to the accumulation of reactive species of O2, such as H2O2, which induces lipid peroxidation. This mechanism may be involved, as a direct consequence of retinal damage, in the pathogenesis of cataract in diabetes.     

Lipid peroxidation in cataract of the human

Lipid peroxidation was investigated as one of the possible mechanisms of cataractogenesis in the human. Malondialdehyde (MDA), a major breakdown product of lipid peroxides, was significantly higher in cataractous lenses as compared to that in normal lenses. 2-Thiobarbituric acid-reactive material, isolated from cortical cataracts and purified by Sephadex G-10 column chromatography, was identified as MDA. In cataractous lenses the enzymic defenses against reactive species of O2 were impaired as evidenced by the significant decrease in activities of superoxide dismutase, catalase and glutathione peroxidase. Hydrogen peroxide in aqueous humor and vitreous humor of human eyes associated with cataract was increased 2-3 fold. It is possible that carbonyl groups of MDA could interact with primary amino groups of proteins and phospholipids of lenticular plasmalemmae by a cross-linking reaction forming Schiff-base conjugates and these mechanisms might be involved in the pathogenesis of cataract.     

Peroxide-metabolizing systems of the crystalline lens

The ability of transparent and cataractous human, rabbit and mice lenses to metabolize hydrogen peroxide in the surrounding medium was evaluated. Using a chemiluminescence method in a system of luminol-horseradish peroxidase and a photometric technique, the temperature-dependent kinetics of H₂O₂ decomposition by lenses were measured. The ability of opaque human lenses to catalyze the decomposition of 10^?4 M H₂O₂ was significantly decreased. However, this was reserved by the addition of GSH to the incubation medium. Incubation of the mice lenses with the initial concentration H₂O₂ 10^?4 M led to partial depletion of GSH in normal and cataractous lenses. Human cataractous lenses showed decreased activities of glutathione reductase, glutathione peroxidase (catalyzing reduction of organic hydroperoxides including hydroperoxides of lipids), superoxide dismutase, but no signs of depletion in activities of catalase or glutathione peroxidase (utilizing H₂O₂). The findings indicated an impairment in peroxide metabolism of the mature cataractous lenses compared to normal lenses to be resulted from a deficiency of GSH. An oxidative stress induced by accumulation of lipid peroxidation products in the lens membranes during cataract progression could be considered as a primary cause of GSH deficiency and disturbance of the redox balance in the lens.     

Evidence of the oxidation of unsaturated fatty acids in cataracts

Gas chromatography analysis with the use of an electron captured detector including preparation of the halogen-substituted derivatives of fatty acids is a useful tool for the detection of lipid peroxidation products both in vitro and in vivo. This technique was applied to determine the content of fatty acid oxy-derivatives in lipid samples of transparent and completely opaque human lenses. At the stage of mature cataract a significantly increased level of oxyproducts was observed in the lens lipid fraction. It was concluded that accumulation of polar oxygroups in the lipid bilayer of plasma membranes of lens fibres is a plausible cause of their damage in cataracts.     

Cataract induction by products of lipid peroxidation

Liposome suspension prepared from the unsaturated phospholipids exposed to lipid peroxidation (LPO) induced posterior subcapsular cataracts after injection into the posterior vitreous of rabbit eyes. In the background of this model lies a type of lens opacity formed during retinal degeneration when toxic peroxide substances diffuse anteriorly through the vitreous body resulting in vitreous opacities and complicated cataracts. Saturated liposomes (prepared from beta-oleoyl-gamma-palmitoyl) L-alpha-lecithin) did not induce lens opacities, which is the evidence that a lipid peroxidation mechanism may be responsible for the posterior cataracts. Along with cataract formation accumulation of LPO fluorescent products in vitreous, aqueous humor and lens was observed. It was followed by a decreased level of reduced glutathione in the lens. The obtained results strongly support the hypothesis of LPO initial role in cataracts.     

Lipid fluorophores of the crystalline lens in cataracts

Microcolumn liquid and column chromatography technique is conjunction with UV-spectrophotometry and spectrofluorescent analysis were used to study lipid peroxidation products accumulated in human lenses during cataract formation by means of chromatographic separation in regard to the molecular weight and polarity properties. Cataract is characterized by the appearance of certain substances changing UV-absorption lipid spectra in the region of 230 and 274 nm and having special fluorescence (excitation--320-370 nm), (emission--405-460 nm). The same changes were observed by ultrasoundinduced lipid peroxidation of model lipid samples. The accumulated lipid peroxidation products are concentrated in the same chromatographic fractions that are responsible for the change of UV-absorption and fluorescent spectra of lipids of cataractous lenses. It is the evidence of free radical lipid peroxidation products accumulation in human lenses at cataract formation. Along with the formation of diene and triene conjugates in the lens lipids, cataract is characterized by the formation of cetodienes and of low molecular weight lipid fluorescent products of fatty acids oxidation with low polarity due to the appearance of tetraene derivatives of polyunsaturated fatty acids. The particular features of mature cataract are an increased intensity of long-wave lipid fluorescence in the blue-green region (430-460 nm) of the spectrum, formation of high molecular weight fluorescent lipid peroxidation products with high polarity, and smooth decrease in absorbance in the region of 220-330 nm. During cataract formation products of deep lipid peroxidation resulting from radical phospholipids and fatty acids polymerisation are accumulated. It is supposed that lipid peroxidation is an initial phase of membrane desintegration and formation of HMW-proteins in cataract.     

用蛋白质印迹转移技术分析正常及硒性白内障大鼠晶状体及房水中蛋白质的性质

本文用蛋白质印迹转移技术分析了正常及硒性白内障大鼠晶状体及房水中蛋白质的性质。结果表明,晶状体中的脲溶性蛋白质可被抗α及抗γ晶体蛋白血清识别,提示α及γ晶体蛋白均为脲溶性蛋白质的主要成份。患白内障时房水中的蛋白质含量明显增加,且主要被抗γ血清识别,而被抗α血清识别的成份很少,表明在大鼠硒性白内障形成过程中,有较多低分子量蛋白质漏出到房水中,且其主要成份为γ晶体蛋白。此外,我们还发现正常及硒性白内障大鼠晶状体膜蛋白质与抗α及抗γ血清起反应的程度及分布有所不同,提示晶状体细胞膜与晶体蛋白之间存在着相互作用。     

Anti-cataractogenic effect of curcumin and aminoguanidine against selenium-induced oxidative stress in the eye lens of Wistar rat pups: An in vitro study using isolated lens

The aim of this study was to investigate whether curcumin and aminoguanidine (AG) prevent selenium-induced cataractogenesis in vitro. On postpartum day 8, transparent isolated lens were incubated in 24 well plates containing Dulbecco's Modified Eagle Medium (DMEM). Isolated lens of group I were incubated with DMEM medium alone. Group II: lenses incubated in DMEM containing 100 μM sodium selenite; group III: lenses incubated in DMEM containing 100 μM sodium selenite and 100 μM curcumin; group IV: lenses incubated in DMEM containing 100 μM sodium selenite and 200 μM curcumin; group V: lenses incubated in DMEM containing 100 μM sodium selenite and 100 μM AG; group V: lenses incubated in DMEM containing 100 μM sodium selenite and 200 μM AG. On day 12, cataract development was graded using an inverted microscope and the lenses were analyzed for enzymic as well as non-enzymic antioxidants, lipid peroxidation (LPO), nitric oxide (NO), superoxide anion (O₂⁻) and hydroxyl radical generation (OH) and inducible nitric oxide synthase (iNOS) activity by Western blotting and RT-PCR. All control lenses in group I were clear (0). In groups II and III, all isolated lenses developed cataract with variation in levels (+++ or ++), whereas isolated lenses from groups IV, V and VI were clear (0). In agreement to this, a decrease in antioxidants and increased free radical generation and also iNOS expression were observed in selenium exposed lenses when compared to other groups. AG (100 μM) was found to be more effective in anti-cataractogenic effect than curcumin (200 μM). Curcumin and AG suppressed selenium-induced oxidative stress and cataract formation in isolated lens from Wistar rat pups, possibly by inhibiting depletion of enzymic as well as non-enzymic antioxidants, and preventing uncontrolled generation of free radicals and also by inhibiting iNOS expression. Our results implicate a major role for curcumin and AG in preventing cataractogenesis in selenite-exposed lenses, wherein AG was found to be more potent.     

Cataract produced by tyrosinase and tyrosine systems in rabbit lens in vitro

1. Cataracts were developed by incubating rabbit lenses for 22hr. at 37 degrees in a culture medium containing tyrosine and tyrosinase (EC 1.10.3.1). 2. A 45% diminution in the content of GSH and significant inhibition of glucose 6-phosphate dehydrogenase (EC 1.1.1.49) activity were observed in the cataractous lenses compared with controls. 3. GSSG accumulated in both cataractous and control lenses. Significant amounts of GSSG were transported outward from the cataractous lenses and small amounts from control lenses. 4. Transport of GSSG from rabbit lens incubated in a diffusate of plasma from a naphthalene-fed rabbit was also observed. 5. GSSG was found in the aqueous humour obtained between 2 and 24hr. after feeding of naphthalene to rabbits; subsequently the GSSG in the aqueous humour decreased to almost undetectable amounts in 48hr.; in controls, GSSG was not detectable. 6. A possible mechanism of formation of experimental and senile cataract is briefly discussed.     

Antioxidant and anticataractogenic effects of topical captopril in diquat-induced cataract in rabbits.

1-[(2s)-3-Mercapto-2-methylpropionyl]-L-proline (captopril), an antihypertensive and free radical scavenger, protected the rabbit lens from peroxidative and oxidative damage induced by 1 mM diquat in vitro. To evaluate the anticataract efficacy of captopril, an experimental group of five rabbits was treated with topical captopril (1% in 0.15 M NaCl, w/v), and 50 microliters was instilled onto both eyes four times a day for a total of 8 weeks. Following the same procedure, the eyes of five rabbits were treated with topical 0.15 M NaCl as a control for captopril treatment. At the end of the first week of treatment, a single intravitreal dose of 120 nmole diquat in 30 microliters of 0.15 M NaCl was injected into the right eye of each rabbit of both the groups. As a control for intravitreal diquat injection, the left eye of all the rabbits were injected with the diluent, 30 microliters per eye. The intravitreal diquat or its diluent injection was only for one time. From slit-lamp biomicroscopic observation of the diquat-injected right eyes, the anticataract effect of captopril in the treatment group was indicated by the finding that in four of five rabbits the cataract did not advance; whereas in four of five rabbits treated with the diluent the cataract progressed to grade 3. The lenses in the diluent-injected control left eyes of the rabbits treated with the captopril or diluent were normal. However, since the number of animals used for the in vivo studies was few, further confirmation of the anticataract effect of captopril is necessary. In diquat-injected right eyes of animals treated with captopril, the integrated rate of O2- production was about 50% less (p less than .001) in the aqueous humor, vitreous humor, and lens, compared with O2-, 33.49 +/- 2.26 microM (mean +/- SEM) in the aqueous humor, 17.12 +/- 0.75 microM in the vitreous humor, and 31.44 +/- 1.29 nmole/g wet weight in the lens of the diquat-injected right eyes treated with the diluent. Similar significant (p less than .01) differences in the production of .OH and H2O2 in eye tissues were also observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lipid peroxidation and cataract formation in experimental diabetes

To investigate the role of lipid peroxidation in diabetic cataractogenesis, malondialdehyde, a breakdown product of lipid peroxidation, was measured in lenses with incipient opacities and in retinas from diabetic rats and in clear lenses and in retinas from normal rats. The malondialdehyde mean values obtained in the transparent and cataractous lenses showed non-significant differences, while non-diabetic rat retinas had a significantly lower mean level of malondialdehyde compared with diabetic rat retinas (p less than 0.01). This indicates that, in streptozotocin-induced diabetic rats, lipid peroxidation is apparently not involved in the development of cataract, but it is quite probably involved in retinal damage. The retina, richer in polyunsaturated fatty acids than other ocular structures, is the elective site of lipid peroxidation and from this membrane peroxidation products might probably diffuse and damage other ocular tissues.     

Change in potassium ion homeostasis of the crystalline lens in mice with hereditary cataracts (the CatFr line)

Fraeser mouse lens morphology and potassium homeostasis were studied. It was shown that just at the age of one month mouse lens exposed "bull" cells which could be observed in patients with senile cataract as well. Nucleated fusiform extended cells were found 4 months later in the central part of the lens which was not typical for this part of the whole normal lens. Studied homogenates of 34 mice with hereditary cataract demonstrated statistically significant increase (1.5-fold about) in K+-content estimated for the whole lens weight as compared to the control group (38 lens). The difference in potassium content in aqueous humor between affected and control animals was statistically indistinguishable. The role of potassium ions in Fraeser cataract pathogenesis is discussed.     

Role of long non‐coding RNA MIAT in proliferation,apoptosis and migration of lens epithelial cells: a clinical and in vitro study

Age‐related cataract is among the most common chronic disorders of ageing and is the world's leading blinding disorder. Long non‐coding RNAs play important roles in several biological processes and complicated diseases. However, the role of lncRNAs in the setting of cataract is still unknown. Here, we extracted total RNAs from the transparent and age‐matched cataractous human lenses, and determined lncRNA expression profiles using microarray analysis. We found that 38 lncRNAs were differentially expressed between transparent and cataractous lenses. 17 of 20 differentially expressed lncRNAs were further verified by quantitative RT‐PCRs. One top abundant lncRNA, MIAT, was specifically up‐regulated both in the plasma fraction of whole blood and aqueous humor of cataract patients. MIAT knockdown could affect the proliferation, apoptosis and migration of Human lens epithelial cells (HLECs) upon oxidative stress. Posterior capsule opacification (PCO) is a common complication of cataract surgery, which is associated with abnormal production of inflammatory factors. MIAT knockdown could repress tumour necrosis factor‐α‐induced abnormal proliferation and migration of HLECs, suggesting a potential role of MIAT in PCO‐related pathological process. Moreover, we found that MIAT acted as a ceRNA, and formed a feedback loop with Akt and miR‐150‐5p to regulate HLEC function. Collectively, this study provides a novel insight into the pathogenesis of age‐related cataract.