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)

Studies have been made of the effects of X-ray on various lens reducing systems, including the levels of NADPH and glutathione (GSH), the activity of the hexose monophosphate shunt (HMS) and of certain enzymes, including GSH reductase, GSH peroxidase, and glucose-6-phosphate dehydrogenase (G-6-PG). It was found that during several weeks following X-irradiation but prior to cataract formation, there was very little change in the number of reduced -SH groups per unit weight of lens protein but that, with the appearance of cataract, there was a sudden loss of protein -SH groups. In contrast, the concentration of GSH in the X-rayed lens decreased throughout the experimental period. Similarly, the concentration of NADPH in the X-rayed lens was found to decrease significantly relative to controls 1 week prior to cataract formation, and the ratio of NADPH to NADP+ in the lens shifted at this time period from a value greater than 1.0 in the control lens to less than 1.0 in the X-rayed lens. A corresponding decrease occurred in the activity of the HMS in X-rayed lenses as measured by culture in the presence of 1-14C-labeled glucose, G-6-PD was partially inactivated in the X-rayed lens. Of the eight enzymes studied, G-6-PD appeared to be the most sensitive to X-irradiation. The data indicate that X-irradiation results in a steady decrease in the effectiveness of lens reducing systems and that when these systems reach a critically low point, sudden oxidation of protein -SH groups and formation of high-molecular-weight protein aggregates may be initiated.
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PMID:The effects of X-irradiation on lens reducing systems. 3 84

In the aetiology and pathogenesis of senile cataract a disturbed glucose utilisation is found. This reflects a loss of activity of some key enzymes for glycolysis in the lens. These enzymes (ALD, G6PDH, HK, LDH, MDH and phosphofructokinase) are zinc metal enzymes. The decrease in activity of these enzymes can be compensated by the administration of specific cations. With zinc one can improve the impaired glucose metabolism occurring in old age. For the prophylaxis and therapy of senile cataract the prolonged administration of zinc aspartate is indicated. In the presence of magnesium deficiency magnesium salts should also be given. Cation eliminating exogenous or endogenous factors must be taken into consideration.
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PMID:[Clinical biochemical aspects of the prophylaxis and therapy of senile cataract with zinc aspartate (author's transl)]. 9 66

Cataracts removed intracapsularly by cryoprobe technique from human diabetics were analyzed for sugars and polyols by gas liquid chromatography. The contents of sorbitol and fructose of lenses followed blood glucose levels at least up to 250 mg/dl. Studies indicate that human lens is capable of synthesizing substantial amounts of polyol pathway metabolites given exposure to high glucose levels such as are prevalent in diabetes. The synthesis of sorbitol was found to be susceptible to quercitrin, an inhibitor of aldose reductase. The implications of these findings in the formation of cataracts in diabetic individuals have been discussed.
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PMID:Implications of aldose reductase in cataracts in human diabetes. 10 20

Immediately after cataract extraction, lenses from diabetic and nondiabetic patients were collected, classified, and assayed or incubated in high-glucose medium. The distribution of cataract types within the diabetic and nondiabetic groups was almost identical. The aldose reductase (AR) inhibitor AY22,284 (Alrestatin) was as effective in blocking sorbitol formation in diabetic as in nondiabetic lenses. While there was no difference in the level of intralenticular glucose, the diabetic lens produced significantly more sorbitol than did the nondiabetic lens. Also, the activity of polyol dehydrogenase (PD) was much lower in the diabetic population. The diabetic lenses swelled slightly more (P <.2) than nondiabetic lenses in high glucose media, and AY22,284 was effective in reducing the swelling of diabetic lenses in 35.5 mM glucose medium. While these results are preliminary, they suggest that diabetes, in some way, may confer on the human lens an increased susceptibility to osmotic stress via the sorbitol pathway. It is also reassuring to note that an AR inhibitor is no less effective in blocking the more active AR in the diabetic than in the nondiabetic lens. The therapeutic implications of this are discussed.
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PMID:Efficacy of Alrestatin, an aldose reductase inhibitor, in human diabetic and nondiabetic lenses. 12 68

In some tissues containing aldose reductase, increased flux through the polyol pathway has been implicated as being causative in diabetic complications (e.g., cataracts, peripheral neuropathy). We have found CP-45,634 (d-6-fluoro-spiro[chroman-4,4'-imidazolidine]-2',5'-dione) to be a highly potent, structurally novel, uncompetitive inhibitor of calf lens aldose reductase (IC50 approximately 5 X 10(-7)M). In a system in which sorbitol accumulation in isolated rat sciatic nerves was monitored in the presence of high (50 mM) glucose concentrations, CP-45,634 produced inhibition of polyol accumulation at levels as low as 1 X 10(-6)M. To determine if in vitro activity would translate to in vivo models, sorbitol accumulation in rat sciatic nerves was measured 27 hr after induction of diabetes with streptozotocin. Orally administered CP-45,634 was effective at dose levels as low as 0.25 mg/kg, t.i.d., and at 0.75 mg/kg produced an 85% inhibition of sorbitol accumulation. Two weeks after induction of diabetes by streptozotocin, sorbitol levels in rat lens and the sciatic nerve rose to 21,203 nmole/gm and 1,161 nmole/gm, respectively. Subsequent oral administration of CP-45,634 (2.5 mg/kg, b.i.d.) for 1 wk reduced these levels by 92% in nerves and 90% in lenses. In galactosemic rats, CP-45,634 inhibited the rise in lens galactitol and effectively delayed cataract formation at oral doses as low as 5 mg/kg/day. These high levels of in vivo activity suggest that CP-45,634 has potential for assessing the role of the polyol pathway in diabetic complications.
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PMID:CP-45,634: a novel aldose reductase inhibitor that inhibits polyol pathway activity in diabetic and galactosemic rats. 12 97

1. Cataract formation in streptozotocin-induced diabetes in rats was reduced by approximately 85% when a diet rich in maize oil (300 g/kg diet) (fat diet) was given, thus confirming results of earlier studies. However, the concentration of sorbitol in the lens of diabetic animals remained high, the values for diabetic rats given the standard diet and the fat died being 65 and 40 mumol/g protein respectively. 2. With the standard diet, the fatty acid profile of the triglycerides of the epididymal fat pads was characterized by a greater relative proportion of saturated fatty acids for the diabetic animals compared to that for the normal animals. The fat diet moderated the tendency towards saturation in the diabetic animals. 3. The fat diet had other effects on the diabetic animals; these included a reduced mortality rate, increased body-weight, a decrease in the daily water intake, and in the daily urinary excretion of glucose and urea. 4. In the diabetic animals the fat diet had no effect on the specific activities in the liver of hexokinase (EC 2.7.1.1), glucokinase (EC 2.7.1.2), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40). However, the specific activity of glucose-6-phosphatase (EC 3.1.3.9) was reduced, while that of malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) was increased. The NAD+:NADH ratio, as calculated from liver pyruvate and lactate concentrations, tended to increase. 5. The results suggested that the fat diet moderated the long-term metabolic effects of diabetes.
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PMID:The effect of an unsaturated-fat diet on cataract formation in streptozotocin-induced diabetic rats. 13 11

The influence of daily subcutaneous cortisol injections (10 mg/kg) on the development of cataracts in streptozotocine (STR) diabetes was studied in 6 groups of Wistar rats (n = 10). Cataracts occurred only in the two groups subjected to high STR doses (60 mg/kg). We were astonished to find that in cortisol-treated diabetic animals there were lower blood glucose levels, fewer cases of glucosuria, and less pronounced cataracts than in rats treated with STR only. As STR had been administered after the start of cortisol therapy, it is assumed that the steroid had caused a protection of pancreatic B cells against STR and the onset of a less severe diabetes.
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PMID:[The influence of cortisol treatment on the development of diabetic cataracts in rats (author's transl)]. 13 12

Cultured fibroblasts derived from a patient homozygous for galactokinase deficiency, his parents, and controls had similar rates of growth in culture media where the only hexose was glucose. However, in media where the only hexose was galactose there was almost no growth of homozygous mutant cells or of maternal heterozygous cells and slight growth of paternal heterozygous cells. Growth of control cells was initially slow, but after a lag period (which coincided with increasing galactokinase activity) growth reached approximately the same levels as in glucose medium. In all cell lines there was a direct relation between the degree of enhancement of galactokinase activity and the ability of cells to adapt to growth in media where the only hexose was galactose. Erythrocyte galactokinase activities in a series of 24 children children with congenital cataracts aged 2-16 years were similar to those in 26 controls. One child in each of the cataract and control groups had 40-50% of mean control activity and was considered to be a potential heterozygote. Galactokinase deficiency (homozygous and heterozygous) is considered to be an uncommon cause of childhood cataracts. Nevertheless, it is an important cause since early dietary treatment can prevent or reverse lens opacities. The heterozygous state may be expressed phenotypically in the patient by the appearance of cataracts and in cultured cells by their defective growth in media where galactose is the only hexose.
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PMID:Phenotypic expression of galactokinase deficiency in heterozygous and homozygous subjects: in vivo and in vitro studies. 18 97

A high glucose concentration in vivo or an increased glucose of glucose 6-phosphate concentration in vitro has been found to lead to the glycosylation of epsilon-amino groups of lysine residues in bovine and rat lens crystallins. In vitro, this glycosylation imparts an increased susceptibility of the crystallins to sulfhydryl oxidation. Disulfide crosslinks result in the formation of high molecular weight aggregates and an opalescence in the crystallin solutions. The addition of reducing agents prevents as well as reverses the formation of high molecular weight aggregates and the opalescence of the crystallins. These phenomena suggest a new interpretation of previous results on cataract formation and a new approach for development of drugs to prevent cataracts.
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PMID:Diabetic cataract formation: potential role of glycosylation of lens crystallins. 27 62

Aqueous fluid was withdrawn from eyes of patients undergoing cataract extraction at various intervals after administration of two drops 2% pilocarpine-HCl in a standard manner. Determination of aqueous pilocarpine concentration was made both by spectroscopy of a ferric hydroxylamine complex and by gas-liquid chromatography. These methods were consistent in indicating that concentration does not rise beyond 5 micrograms/ml at any time following topical instillation. The mean of 71 GLC determinations of aqueous tapped between 2 and 32 minutes after drops was 1.67 micrograms/ml. With assumption of a total chamber volume of 400 microliter, the average total pilocarpine in aqueous in these circumstances is less than 1 microgram. These findings correlate well with investigations of transcorneal flux of pilocarpine for the rabbit in a partial in vitro transport chamber system, with which comparable low flux efficiency was found after simulated drop administration. This serves to validate in some measure in extrapolation of other findings in chamber experiments to the living human eye. The combined in vitro and in vivo experimental results suggest that two distinct mechanisms govern the flux of pilocarpine across the cornea. High doses, comparable to those in standard clinical use, whether administered in drops or in constant flow, are transported inefficiently with kinetics indicating a diffusional mechanism and are associated with intracorneal retention or degradation of a substantial moiety. Low doses, if continuously applied, are much more efficiently transported. Hydrogel polymer vehicles appear to mobilize this low-dose mechanism by retaining drug against mechanical dissipation and elution by tear flow, but also by retaining drug against the capability of the cornea to take up more pilocarpine than can be transported to produce an intracorneal drug "depot." Although the exact nature of the "depot" is not clear, it is not elutable as pharmacologically active drug. It is consistently associated with the relatively poor flux efficiency found with high doses, and thus may act in some manner to disable a more efficient mechanism. The flux efficiency found with hydrogel mediation is more than double the best found in constant flow determinations. Vehicular mediated flux is rate limited by the cornea, independent of dose, linear with time despite exponentially secreasing available drug, and not associated with an intracorneal drug "depot." These features are consistent with carrier mediation of some type.
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PMID:Flux of topical pilocarpine to the human aqueous. 75 81


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