Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has previously been shown that TEMPOL, n-propyl gallate and deferoxamine, compounds that limit the availability of Fe+2 and prevent the generation of hydroxyl radicals, protect cultured rabbit lens epithelial cells from H2O2-induced damage. In view of the importance of glutathione as an antioxidant and the decrease in GSH that is known to accompany most forms of cataract, we investigated whether these compounds protected cultured lens epithelial cells from H2O2 when the cells were artificially depleted of glutathione. Treatment of lens epithelial cells with 1-chloro-2,4-dinitrobenzene (CDNB), a compound that irreversibly binds to glutathione, or buthionine sulfoximine (BSO), an inhibitor of glutathione biosynthesis, reduced the glutathione content to an average of 15-20% of the control values without a concomitant increase in oxidized glutathione. Morphological changes were assessed by phase contrast and electron microscopy. In order to assess growth, cells in 5 ml serum-free MEM were exposed to an initial concentration of 0. 05 mm H2O2 (for 50,000 cells) or 2 doses of 0.5 mm H2O2 (for 800,000 cells). After exposure to H2O2, medium was replaced with MEM plus 8% rabbit serum; cells were fed on days 3 and 6 and counted on day 7. When 50,000 or 800,000 cells with decreased glutathione were exposed to 0.05 or 0.5 mm H2O2 the H2O2 was cytotoxic, whereas cells treated with H2O2 alone remained viable but showed inhibited proliferation. An unexpected finding was that cells continued to remove H2O2 from the medium at normal rates even when the GSH level was reduced. Cells treated with CDNB or BSO alone exhibited morphological and growth properties comparable to untreated cells. Cells treated with CDNB or BSO and then with H2O2 exhibited decreased cell-to-cell contact, nuclear shrinkage, and arborization when viewed with phase-contrast microscopy and showed extensive nuclear and cytoplasmic degeneration at the EM level. Cell death was determined by dye exclusion and confirmed by video microscopy. When cells were treated with CDNB or BSO and subsequently treated with TEMPOL, n-propyl gallate or deferoxamine and then challenged with H2O2 cytotoxicity was prevented and the cells were capable of growth. The data show that H2O2 was not lethal to glutathione-depleted lens epithelial cells when they were treated with compounds that prevented the generation of reactive oxygen species. In addition, the results indicate that GSH has an important protective role independent of its ability to decompose H2O2 via glutathione peroxidase.
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PMID:Protection from oxidative insult in glutathione depleted lens epithelial cells. 998 49

Oxidative damage of the lens causes disulfide bonds between cysteinyl residues of lens proteins and thiols such as glutathione and cysteine, which may lead to cataract. The effect of H2O2 oxidation was determined by comparing bovine lenses incubated with and without 30 mM H2O2. The H2O2 treatment decreased the glutathione and increased the protein-glutathione and protein-cysteine disulfides in the lens. The molecular mass of the gammaB-crystallin isolated from lenses, not treated with H2O2, agreed with the published sequence (Mr 20,966). Some lenses also had a less abundant gammaB-crystallin component 305 Da higher (Mr 21,270), suggesting the presence of a glutathione adduct. The gammaB-crystallins from H2O2 treated lenses had three components, the major one with one GSH adduct, another one with the mass of unmodified gammaB-crystallin, and a third with a mass consistent with addition of two GSH adducts. Mass spectrometric analysis of tryptic peptides of gammaB-crystallins from different lenses indicated that the +305 Da modifications were not at a specific cysteine. For the lenses incubated without H2O2, there was evidence of adducts at Cys-41 and in peptide 10-31, which includes 3 cysteines. Analysis of modified peptide 10-31 by tandem mass spectrometry showed GSH adducts at Cys-15, Cys-18, and Cys-22. In addition, gammaB-crystallins from H2O2-treated lenses had an adduct at Cys-109, partial oxidation at all 7 Met residues, and evidence for two disulfide bonds.
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PMID:Thiolation of the gammaB-crystallins in intact bovine lens exposed to hydrogen peroxide. 998 10

Utilizing a human beta-actin promoter, a catalase cDNA expression vector was constructed. This construct was used to transfect two immortal cell lines, mouse alpha TN4-1 and rabbit N/N 1003A. The catalase activity was increased about 3.4 fold in the alpha TN4-1 cells and 38 fold in the N/N 1003A cells. Some changes in other enzyme activities were also observed as a result of the transfections. Surprisingly, the ability to degrade H2O2 in the extracellular environment of the cells did not markedly change as a result of the catalase amplification. However, the ability to resist H2O2 stress was dramatically altered. Non-protein thiol (NP-SH) levels, choline uptake and glyceraldehyde phosphate dehydrogenase (GPD) activity were all markedly decreased in the non-transfected cells when they were subjected to 300 microM H2O2. However, in both transfected cell lines, these parameters remained in the normal range during H2O2 stress. The results obtained upon observing aspects of DNA metabolism were more complicated. While on H2O2 stress, non-transfected cell lines showed a marked decrease in thymidine incorporation, only the transfected alpha TN4-1 line remained in the normal range. Thymidine incorporation in transfected rabbit N/N 1003A cells was decreased compared to normal cells. In contrast, studies on single strand DNA breaks indicated that transfected rabbit cells had little damage compared to the significant DNA damage observed in the normal cells. The normal N/N 1003A cells were also much more susceptible to H2O2 induced damage than normal alpha TN4-1 cells, suggesting that the high GSH peroxidase activity observed in the rabbit cells may be detrimental since the low glutathione reductase activity in such cells results in an accelerated depletion of glutathione. The overall results suggest that augmenting lens catalase may prevent cataract development caused by H2O2 stress.
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PMID:The effect of catalase amplification on immortal lens epithelial cell lines. 999 Mar 30

The relationship between sugar cataract formation and radical production was investigated. The in vivo formation of free radicals in the lenses of rats fed on a diet containing 25% and 50% galactose was studied using the electron spin resonance (ESR) spin trapping method. Effects of treatment with aldose reductase inhibitor (ARI) SNK-860 on free radical formation were determined in 25% and 50% galactose fed rats. Hydroxyl radical (*OH) adduct of the spin trap 5,5'-dimethyl-1-pyrroline- N -oxide (DMPO) was directly detected in the superficial cortical cataract obtained from 25% and 50% galactose-fed rats. *OH production was completely inhibited by ARI SNK-860 in both galactose groups. Polyol accumulated in rat lenses given 50% galactose with a peak within the first 2 weeks, and was significantly inhibited by SNK-860. The increase in *OH production was considered with the polyol accumulation in both galactose groups. The dose of SNK-860 to inhibit *OH by 50% level was estimated at 3 m by the method of kinetic competition in vitro experiment. SNK-860 is not an effective *OH scavenger compared to other *OH scavengers. The results of the present study suggest that *OH is indirectly inhibited by SNK-860 resulting from decreasing polyol and *OH formation is related to sugar cataract formation in early stages, possibly via the Fenton reaction involving H2O2 produced from the activated polyol pathway. We suppose that *OH may accelerate damage to the cell membrane of lens fibers resulting from polyol accumulation *OH may play an important role in the early stage of sugar cataract process.
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PMID:Cataract formation through the polyol pathway is associated with free radical production. 1019 3

Cataract results from oxidative damage to the lens. The mechanism involves disruption of the redox system, membrane damage, proteolysis, protein aggregation and a loss of lens transparency. Diet has a significant impact on cataract development, but the individual dietary components responsible for this effect are not known. We show that low micromolar concentrations of the naturally-occurring flavonoid, quercetin, inhibit cataractogenesis in a rat lens organ cultured model exposed to the endogenous oxidant hydrogen peroxide. Other phenolic antioxidants, (+)epicatechin and chlorogenic acid, are much less effective. Quercetin was active both when incubated in the culture medium together with hydrogen peroxide, and was also active when the lenses were pre-treated with quercetin prior to oxidative insult. Quercetin protected the lens from calcium and sodium influx, which are early events leading to lens opacity, and this implies that the non-selective cation channel is protected by this phenolic. It did not, however, protect against formation of oxidized glutathione resulting from H2O2 treatment. The results demonstrate that quercetin helps to maintain lens transparency after an oxidative insult. The lens organ culture/hydrogen peroxide (LOCH) model is also suitable for examining the effect of other dietary antioxidants.
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PMID:Quercetin inhibits hydrogen peroxide-induced oxidation of the rat lens. 1021 52

While many experimental studies have shown a protective effect of vitamin C in age-related cataract, other studies have revealed contrasting roles for this nutrient. Oxidative damage in the lens can be prevented by vitamin C. However, a pro-oxidant effect of vitamin C through H2O2 generation has been suggested. Vitamin C has also been shown to play a role in protein glycation, which is observed in cataract formation. A protective effect of dietary energy restriction appears to be inversely related to plasma vitamin C levels in rodents. Moreover, conclusions from human epidemiological and intervention studies are not uniform. The available evidence suggests that maintenance of sufficient plasma vitamin C is needed to prevent oxidative damage in the lens. More research will be needed in order to confirm the relative importance of of the different roles of vitamin C in the eye lens.
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PMID:A possible role for vitamin C in age-related cataract. 1046 70

The extent of glycation of human eye lens proteins with glucose in presence of added inositol was examined in vitro using [U14C] glucose. Lens homogenate was reacted with varying concentrations of glucose and glucose + inositol. At the end of the reaction, the proteins were precipitated with TCA, centrifuged, dissolved in NaOH and the radioactivity was measured. Inositol decreased the glycation by 57-67%. Pure inositol and glucose suitably labelled with 3H or 14C when reacted and followed by paper chromatography and HPLC showed that glucosyl inositol was present along with unreacted free glucose. Preliminary studies made of the UV spectra of pure inositol (i) when reacted with H2O2 showed that inositol removed H2O2 from the reaction mixture (ii) when reacted with arachidonic acid showed that they formed a conjugate. The observations indicate that the antioxidant property of inositol could be the result of its' quenching action on reactive oxygen, intermediates and conjugate-formation with compounds like arachidonic acid and the antiglycating property due to scavenging of glucose. The antioxidant and the antiglycating properties of inositol may be beneficial in delaying or averting cataract.
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PMID:Two new functions of inositol in the eye lens: antioxidation and antiglycation and possible mechanisms. 1054 73

3-Hydroxykynurenine (3OHKyn), the precursor of UV filters in human lens, is highly autooxidizable, generates H2O2, and binds to lens proteins, yielding a tanned/yellow product resembling senile nuclear cataractous materials. Thus, if 3OHkyn can be shown to be the causative agent in cataract, it may be possible to prevent the disease by lowering the level of 3OHKyn. To this end, indoleamine 2,3-dioxygenase, the first enzyme in UV filter synthesis, was studied using lens epithelial cell lines. The results indicated that the IDO expression is mediated by IFN-gamma. Immuno-suppressants which inhibit production of IFN-gamma may act as anti-cataract agents. Another way to lower the level of 3OHKyn is to use specific inhibitors for IDO. A recombinant human IDO was expressed to develop the inhibitors.
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PMID:Regulation of indoleamine 2,3-dioxygenase, the first enzyme in UV filter biosynthesis in the human lens. Relevance for senile nuclear cataract. 1072 Oct 62

The reducing compound glutathione (GSH) exists in an unusually high concentration in the lens where it functions as an essential antioxidant vital for maintenance of the tissue's transparency. In conjunction with an active glutathione redox cycle located in the lens epithelium and superficial cortex, GSH detoxifies potentially damaging oxidants such as H2O2 and dehydroascorbic acid. Recent studies have indicated an important hydroxyl radical-scavenging function for GSH in lens epithelial cells, independent of the cells' ability to detoxify H2O2. Depletion of GSH or inhibition of the redox cycle allows low levels of oxidant to damage lens epithelial targets such as Na/K-ATPase, certain cytoskeletal proteins and proteins associated with normal membrane permeability. The level of GSH in the nucleus of the lens is relatively low, particularly in the aging lens, and exactly how the compound travels from the epithelium to the central region of the organ is not known. Recently, a cortical/nuclear barrier to GSH migration in older human lenses was demonstrated by Sweeney et al. The relatively low ratio of GSH to protein -SH in the nucleus of the lens, combined with low activity of the glutathione redox cycle in this region, makes the nucleus especially vulnerable to oxidative stress, as has been demonstrated with use of in vivo experimental animal models such as hyperbaric oxygen, UVA light and the glutathione peroxidase knockout mouse. Effects observed in these models, which are currently being utilized to investigate the mechanism of formation of human senile nuclear cataract, include an increase in lens nuclear disulfide, damage to nuclear membranes and an increase in nuclear light scattering. A need exists for development of therapeutic agents to slow age-related loss of antioxidant activity in the nucleus of the human lens to delay the onset of cataract.
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PMID:Glutathione: a vital lens antioxidant. 1080 23

The high content of glutathione (GSH) in the lens is believed to protect the thiols in structural proteins and enzymes for proper biological functions. The lens has both biosynthetic and regenerating systems for GSH to maintain its large pool size (4-6 mM). However, we have observed that, in aging lenses or lenses under oxidative stress, the size of GSH pool is diminished; and some protein thiols are being S-thiolated by oxidized nonprotein thiols to form protein-thiol mixed disulfides, either as protein-S-S-glutathione (PSSG) or protein-S-S-cysteine (PSSC). We have shown in an H2O2-induced cataract model that PSSG formation precedes a cascade of events starting with protein disulfide crosslinks, protein solubility loss, and eventual lens opacification. Recently, we discovered that this early oxidative damage in protein thiols could be spontaneously reversed in H2O2 pretreated lenses if the oxidant was removed in time. This dethiolation process is likely mediated through a redox regulating enzyme, thioltransferase (TTase), which has been discovered recently in the lens. To understand if the role of oxidative defense and repair is the physiological function of TTase in the lens, we cloned the TTase gene and purified the recombinant human lens TTase. Although TTase required GSH for its activity, TTase was far more efficient in dethiolating lens proteins than GSH alone. It favored PSSG over PSSC and dethiolated gamma-crystallin-S-S-G better than the alpha-crystallin counterparts. Furthermore, TTase showed a remarkable resistance to oxidation (H2O2) in cultured rabbit lens epithelial cells when GSH peroxidase, GSH reductase, and glyceraldehyde-3-phosphate dehydrogenase were severely inactivated. We further showed that activity loss in those SH sensitive enzymes could be attributed to S-thiolation, but reactivation via dethiolation could be attributed to TTase. We conclude that TTase can regulate and repair the thiols in lens proteins and enzymes through its dethiolase activity, thus contributing to the maintenance of the function of the lens.
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PMID:Thiol regulation in the lens. 1080 24


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