Crystalline lens induction of lipid peroxidation

The level of lipid peroxidation products (LPP) was determined in the aqueous humor from the anterior chamber of patients with cataract and donor eyes. The content of LPP in senile cataract aqueous humor was shown to be significantly increased. To determine the possible mechanism of LPP increase in aqueous humor, human lenses at different stages of cataract as well as transparent human and rabbit lenses were incubated for 3 hours in 3.0 ml medium containing liposomes (0.5 mg/ml) prepared from phospholipids from the egg yolk and 0.14 M NaCl + 0.01 M TRIS-HCl buffer, pH 7.4). Corrections were made for phospholipid autooxidation. The level of LPP accumulation in the medium was determined by MDA assay. The rate of LPP production increased significantly in transparent lenses and in early senile cataract, as compared to controls and advanced (mature) cataracts. EDTA (1 mM), superoxide dismutase (114 u/sample), catalase (900 u/sample), chelated iron (III): Fe3+-ADP addition to the incubation medium depressed the level of LPP accumulation. This suggests the participation of Fe2+, O2-., H2O2 in the mechanism of LPP production in the lens. The induction of lipid peroxidation in the lens can be significant for leukotriene and prostaglandin synthesis in the eye.     

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.     

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.     

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.     

The chemical nature of the fluorescing products accumulating in the lipids of the crystalline lenses of mice with hereditary cataract

The content of diene conjugates (lipid hydroperoxides) was shown to be significantly higher in lipids extracted from the lenses of mice with hereditary cataract than in the controls. The same holds true for characteristics of fluorescence of the end-product of lipid peroxidation. Two (low- and high-molecular weight) peaks were detected in chromatographic lipid profile of cataract lenses measured by fluorescence on Sephadex LH-20 column, whereas only one (high-molecular weight) peak was found in lipids from normal lenses. It was established that high-molecular weight fluorescent fractions corresponded to lipid components of lipofuscin-like pigments. NMR and mass spectrometry of low-molecular weight fractions suggested that they contained predominantly products of free radical oxidation of long chain polyunsaturated fatty acids (C22:6).     

四种中草药抗白内障形成中晶状体脂类过氧化水平及脂类含量的变化

我们观察了中草药防治大鼠半乳糖性白内障形成中脂类含量的变化及脂类过氧化水平。结果表明,与正常晶状体相比,白内障晶状体中总脂类的含量明显降低,总胆固醇的含量及脂类过氧化水平明显升高,总脂类与总胆固醇之比明显下降。而同时分别用黄苓、石斛、菟丝子及玉蝴蝶四种中草药水煎剂灌胃的大鼠晶状体中,总胆类与总胆固醇的含量基本恢复至正常;脂类过氧化水平虽仍高于正常晶状体,但也明显低于白内障晶状体,表明脂类过氧化参与了白内障的形成,上述四种中草药具有抑制脂类过氧化的作用。     

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.     

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.     

The effect of L-DOPA on the accumulation of lipid peroxidation products in separate brain structures during irradiation

A study was made of the effect of L-DOPA on the dynamics of changes in lipid peroxidation products (LPP) and the content of various types of SH groups in certain brain structures (oblongata, cerebellum, visual and sensorimotor cortex) and their synaptosomal fractions upon irradiation. The preadministration of L-DOPA to irradiated rats inhibited LPP accumulation, prevented the decrease in the content of various types of thiols and thus exerted an antioxidant effect.     

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.     

NMR study of the state of water in the human lens during cataract development

Water proton spin-spin relaxation times (T2) and the content of bound, "non-freezable" at -9 degrees C water in both normal human lenses and human lenses of different stages of cataract progression (cataracta incipiens, nondum matura, mature hypermatura) were measured by NMR spin echoes method. By the stage of cataracta nondum matura, increase of bound water content and simultaneous, almost half decrease of the relaxation time (T2), were observed. However, on the following stages of cataract evaluation (almost mature, mature cataracts) a gradual decrease of bound water content is noted, but only for the mature cataract stage the water content significantly differs from that of the normal one. On the stage of hypermature cataract the presence of two unexchanged with each other fractions of water is found. The obtained data are explained by lens protein reconstructions during the cataract progression.     

Serum lipid peroxide levels of albino rats administered naphthalene

When naphthalene was administered at a daily dose of 1 g/kg body weight to Wistar strain rats, their serum lipid peroxide levels were increased on the 4th day after the first administration and reached a maximum on the 7th day. This seems to be due to lipid peroxidation in the liver, in which lipid peroxide levels were increased in a similar pattern as those in the serum. The content of reduced glutathione in lenses of naphthalene-administered rats decreased on the 4th day. These results suggest that in naphthalene-induced cataract in albino rats increased lipid peroxides in the bloodstream may play a role in cataractogenesis.     

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.     

Reactivity of mononuclear phagocytes in the lungs and liver of rats exposed to low temperatures

A study was made of lung and liver mononuclear phagocytes of rats exposed to severe cold (-7 degrees C). The data indicate the depression of mononuclear phagocytes under short-term (2 h) exposure to cold followed by activation of phagocytes, which was more demonstrable in the lungs. The phase modifications in the activity of mononuclear phagocytes were associated with accumulation of lipid peroxidation products (LPP) and destruction of alveolocytes. The different accumulation of LPP in the test organs of animals exposed to cold is regarded by the authors as a possible reason for functional differences of lung and liver macrophages.     

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.     

Study of soluble proteins of mouse crystalline lenses (normal and in cataract)

The water-soluble proteins from mice lenses (normal and cataract lenses) were investigated by methods of absorption spectrophotometry and kinetics of UV-induced radical decay. General characteristic of internal structure of extraction proteins was investigated by recombination kinetic method. It was shown that concentration of water-soluble proteins lowered ten times in lenses of mature cataract, i. e. 90% protein molecules were connected in lenses of mature cataract.     

C-Phycocyanin Modulates Selenite-Induced Cataractogenesis in Rats

The present investigation is aimed to evaluate the anticataractogenic potential of C-phycocyanin (C-PC), extracted and purified from Spirulina platensis. Enucleated rat lenses were maintained in vitro in Dulbecco’s modified Eagle medium (DMEM). Group I contained DMEM, Group II and Group III contained 100 μM of sodium selenite, Group III was subdivided into three viz IIIa, IIIb, IIIc supplemented with 100, 150, 200 μg of C-PC respectively. In the in vivo study, on tenth day post partum: Group I rat pups received an intraperitoneal injection of saline, Group II, IIIa, IIIb, and IIIc rat pups received a subcutaneous injection of sodium selenite (19 μmol/kg bodyweight) Group IIIa, IIIb, IIIc also received an intraperitoneal injection of 100, 150, 200 mg/kg body weight of C-PC, respectively, from postpartum days?9–14. On termination of the experiment, the lenses from both in vitro and in vivo studies were subjected to morphological examination and subsequently processed to estimate the activities of antioxidant enzymes namely superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, levels of reduced glutathione and lipid peroxidation products. Sodium selenite-exposed, C-PC-treated rat lenses (Group IIIc), showed significant restoration of antioxidant enzyme activity (p?<?0.05) when compared to their counterpart Group II. Group IIIc conserved the levels of GSH and lipid peroxidation products at near to normal levels as compared with Group II. Results conclude the possible role of C-PC in modulating the antioxidant enzyme status, thereby retarding sodium selenite-induced cataract incidence both in vitro and in vivo.     

三硝基甲苯致晶体氧化损伤的研究

采取大鼠晶体体外培养的方法,动态观察了在三硝基甲苯作用下,晶体中脂类过氧化、维生素Ｃ含量及超氧化物歧化酶活性的改变,并与对照组进行比较。发现随着三硝基甲苯作用时间的增加,晶体中脂类过氧化增高;维生素Ｃ含量呈下降趋势;超氧化物歧化酶活性在第１天升高,第５天下降。     

Effects of lipid peroxidation products on the rat lens in organ culture: a possible mechanism of cataract initiation in retinal degenerative disease

Rat lenses in organ culture which are exposed to bovine rod outer segments (ROS) or to the major fatty acid of ROS, docosahexaenoic acid, are impaired in their ability to accumulate radiolabeled compounds which lenses normally accumulate by active processes. The extent of lens damage correlates well with the extent of lipid peroxidation in the culture medium as assessed by the thiobarbituric acid assay. Addition of vitamin E to the medium inhibits the effect on the lens while addition of Fe-ADP complexes potentiates the effect. Thus, the lens damage appears to be attributable to toxic species generated by peroxidation of the polyunsaturated lipid added to the culture medium. Toxic aldehyde products appear to be major mediators of the lens damage, since semi-carbazide, which avidly reacts with aldehydes, can protect lenses in this system. These findings may have relevance to the cataracts clinically associated with retinal degenerative diseases such as retinitis pigmentosa. The highly membranous photoreceptor cells are extremely rich in polyunsaturated lipid. Degeneration of these cells, which is the primary pathology in such diseases, would likely lead to peroxidation with generation of toxic products within the eye. Such products could potentially produce secondary damage to other ocular structures including the lens.     

Characterization of dominant hereditary cataract in DDD/1 mice

We found a female cataractous DDD/1-nu/+ mouse and established a hairy mutant strain (DDD/1-Cti/Cti) with 100% incidence of cataract from it by repeating sibmating. Genetic studies demonstrated that a single autosomal semidominant gene controls cataractogenesis. This gene was named Cti. In homozygotes, DDD/1-Cti/Cti, the lenses began to opacify at 14 days of fetal life and were recognized clinically as cataract at 13-14 days of age when the eyes first open. The opacification became more and more intense with age and looked like mature cataract at 28-42 days of age. However, clarification of the opacified lenses commenced at the periphery after 56 days of age and expanded to the inside with time, and only an opaque spot was left at the center at 140 days of age. In heterozygotes, DDD/1-Cti/+, the lenses were recognizable as cataract after 28 days and became like mature cataract around 35 days of age. The opacity began to be lightened at 42 days and the lenses appeared normal at 56 days of age. Both lenses and eyeballs developed in similar courses in DDD/1(-)+/+, -Cti/+ and -Cti/Cti, although slightly retarded in the last. Microphthalmia was not accompanied even in DDD/1-Cti/Cti. The lens water content remained higher during the time when intense lens opacity continued in DDD/1-Cti/Cti and -Cti/+. Background genes appeared to affect the expression of Cti. DDD/1-Cti(-)+ mice may provide a model for researches into clarification of opaque lenses. A discussion concerning the possible allelism of Cti and Cts with Lop was made based on their phenotypic characteristics.