Pharmacological inhibition of diabetic retinopathy: aminoguanidine and aspirin.

Effects of aminoguanidine and aspirin on the development of retinopathy have been examined in 5-year studies of diabetic dogs. Either agent was administered daily in doses of 20-25 mg. kg(-1).

Retinal glutamate in diabetes and effect of antioxidants.

Diabetes results in various biochemical abnormalities in the retina, but which of these abnormalities are critical in the development of retinopathy is not known. The aim of this study is to examine the effect of antioxidant supplementation on diabetes-induced alterations of retinal glutamate, and to explore the inter-relationship between alterations of retinal glutamate, oxidative stress, and nitric oxide (NO) in diabetes. Glutamate was measured in the retina at 2 months of diabetes in rats receiving diets supplemented with or without a mixture of antioxidants containing ascorbic acid, Trolox, DL alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene and selenium.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia VIII. Prevention by aminoguanidine.

Purpose: Aminoguanidine has been found to inhibit the development of some retinal lesions in diabetic rats and diabetic dogs, thereby raising a possibility that the formation of glycation end products (AGEs) may be an essential step in the pathogenesis of the retinopathy. The purpose of this study is to investigate the effect of aminoguanidine administration on other metabolic abnormalities which might be involved in the development of retinopathy in two models of the retinopathy, alloxan diabetes and experimental galactosemia.

Methods: Oxidative stress, nitric oxide (NO) and the activity of protein kinase C (PKC, total activity) were measured in the retina of the rats experimentally diabetic or galactosemic for 2 months.

Diabetes-induced metabolic abnormalities in myocardium: effect of antioxidant therapy.

Effects of hyperglycemia (both diabetes and experimental galactosemia) on cardiac metabolism have been determined. In addition, the effect of supplemental antioxidants on these hyperglycemia-induced abnormalities of cardiac metabolism has been investigated. Diabetes or experimental galactosemia of 2 months duration in rats significantly increased oxidative stress in myocardium, as demonstrated by elevation of thiobarbituric acid reactive substances (TBARS) and lipid fluorescent products in left ventricle.

Aldose reductase and the development of renal disease in diabetic dogs.

Effects of 5 years administration of an aldose reductase inhibitor (Sorbinil) on renal structure and albumin excretion were evaluated in diabetic dogs. Glycemia, estimated by frequent measurements of HbA1, glycated plasma proteins and glucosuria, was kept comparable between the placebo- and Sorbinil-treated diabetic groups. Kidney structure was evaluated using morphometric techniques by light and electron microscopy, and excretion of immunoreactive albumin was measured yearly.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia. VI. Comparison of retinal and cerebral cortex metabolism, and effects of antioxidant therapy.

Metabolic abnormalities observed in retina and in cerebral cortex were compared in diabetic rats and experimentally galactosemic rats. Diabetes or experimental galactosemia of 2 months duration significantly increased oxidative stress in retina, as shown by elevation of retinal thiobarbituric acid reactive substances (TBARS) and subnormal activities of antioxidant defense enzymes, but had no such effect in the cerebral cortex. Activities of sodium potassium adenosine triphosphatase [(Na,K)-ATPase] and calcium ATPase became subnormal in retina as well as in cerebral cortex.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia: V. Relationship between protein kinase C and ATPases.

In the retinas of diabetic animals, protein kinase C (PKC) activity is elevated, and Na+-K+-ATPase and calcium ATPase activities are subnormal. These abnormalities are also present in another model of diabetic retinopathy, experimental galactosemia. We have investigated the relationship between hyperglycemia-induced abnormalities of PKC and ATPases using a selective inhibitor of beta isoform of PKC (LY333531).

Abnormalities of retinal metabolism in diabetes or experimental galactosemia. IV. Antioxidant defense system.

Activities of enzymes that protect the retina from reactive oxygen species were investigated in experimentally diabetic rats and experimentally galactosemic rats, two animal models known to develop vascular lesions consistent with diabetic retinopathy. Diabetes or experimental galactosemia of 2 months duration significantly decreased the activities of glutathione reductase and glutathione peroxidase in the retina while having no effect on the glutathione synthesizing enzymes glutathione synthetase and gamma-glutamyl cysteine synthetase. Activities of two other important antioxidant defense enzymes-superoxide dismutase (SOD) and catalase-also were decreased (by more than 25%) in retinas of diabetic rats and galactosemic rats.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia. III. Effects of antioxidants.

Effects of antioxidants on hyperglycemia-induced alterations of retinal metabolism were evaluated in rats diabetic or experimentally galactosemic for 2 months. Oxidative stress was estimated by measuring lipid peroxides (measured as thiobarbituric acid reactive substances [TBARS]) in retina and plasma. Erythrocyte osmotic fragility, another measure of oxidative stress, also was determined in the same groups of rats.

A mouse model of diabetic retinopathy.

Objective: To obtain a model of diabetic retinopathy to which modern methods of genetic engineering may be applied, by determining the response of 2 strains of mice to long-term galactose feeding.

Methods: Both C57BL/6 mice BALB/c mice were fed each of 2 galactose-rich diets (30% and 50% galactose), and trypsin digests of their retinas were compared with those of controls at durations of up to 26 months.

Results: The mortality rate in galactose-fed animals was lower in C57BL/6 mice than in BALB/c mice, and both strains tolerated the 30% galactose diet significantly better than the 50% galactose diet.

Evidence of a glycemic threshold for the formation of pentosidine in diabetic dog lens but not in collagen.

The relationship between long-term glycemic control and the advanced Maillard reaction was investigated in dura mater collagen and lens proteins from dogs that were diabetic for 5 years. Diabetic dogs were assigned prospectively to good, moderate, and poor glycemic control and maintained by insulin. Biochemical changes were determined at study exit.

Capillary lesions develop in retina rather than cerebral cortex in diabetes and experimental galactosemia.

Objective: To isolate microvessels from cerebral cortex of dogs with alloxan-induced diabetes and dogs with experimental galactosemia to compare the prevalence of microvascular lesions in cerebral cortex with that in retina.

Methods: Microvessels were isolated from cerebral cortex of experimental animals using a sieving method, and compared with the retinal vasculature isolated from the same animals using the trypsin digestion method.

Results: Dogs with diabetes or experimental galactosemia of 5 years' duration had retinopathy that was morphologically indistinguishable from that of humans with diabetes, including microaneurysms, acellular capillaries, and pericyte ghosts.

Vascular lesions in diabetes are distributed non-uniformly within the retina.

Microaneurysms, acellular capillaries and pericyte ghosts are characteristic of diabetic retinopathy, but it is not clear what causes these lesions or whether they are causally related to each other. The distribution of microaneurysms, acellular capillaries and pericyte ghosts has been evaluated in two animal models of diabetic retinopathy, diabetic dogs (n = 25) and galactose-fed dogs (n = 12). After 5 years of diabetes or galactosemia, retinas were divided into four quadrants at the optic disk, prepared by the trypsin-digest method, and the frequency of the lesions compared among the quadrants.

Retinopathy in galactosemic dogs continues to progress after cessation of galactosemia.

Background: Progression of diabetic retinopathy in human subjects and animal models is difficult to halt promptly by intensified insulin therapy and strict glycemic control.

Objective: To learn whether this resistance to arrest is peculiar to diabetes and insulin therapy or is a characteristic of hyperglycemia itself, we have determined the effect of intervention on diabetic-like retinopathy in a non-diabetic animal model, the galactose-fed dog.

Methods: Dogs were given a 30% galactose diet.

Galactose-induced retinal microangiopathy in rats.

Purpose: The suitability of the galactose-fed rat as a model of diabetic retinopathy was examined in nondiabetic rats fed diets enriched with either 30% or 50% galactose for up to 2 years.

Methods: Retinal capillaries were examined by light and electron microscopy, and the prevalence or severity of diabetic-like lesions was quantitated.

Results: Histologic evaluation of trypsin digests of retina revealed significantly greater than normal frequencies of pericyte ghosts and acellular capillaries at both 15 and 23 months receiving a 50% galactose diet.

Abnormalities of retinal metabolism in diabetes or galactosemia. II. Comparison of gamma-glutamyl transpeptidase in retina and cerebral cortex, and effects of antioxidant therapy.

Levels of the intracellular antioxidant, glutathione, become subnormal in retina in diabetes or experimental galactosemia. In order to investigate the cause and significance of this abnormality, activity of gamma-glutamyl transpeptidase (an enzyme important in the synthesis and degradation of glutathione) and levels of reduced glutathione have been measured in retinas of diabetic rats and dogs and of experimentally galactosemic rats and dogs. Retinal gamma-glutamyl transpeptidase activity and glutathione level were significantly less than normal after 2 months of diabetes or galactosemia.

Comparison of retinal lesions in alloxan-diabetic rats and galactose-fed rats.

Galactose-fed rats develop a retinal microvascular disease, but retinopathy has not been found to develop reproducibly in diabetic rats. We sought to determine which retinal lesions can be reproducibly produced by long-term diabetes in rats, the extent to which the capillary lesions in diabetic rats and galactosemic rats are similar, and whether the retinopathy induced by 50% galactose can be reproduced satisfactorily by a lower concentration of galactose. Alloxan-diabetic rats and rats fed either a 50% galactose diet or a 30% galactose diet were killed after comparable durations of study (18 to 22 months).

Characterization of the mechanism for the chronic activation of diacylglycerol-protein kinase C pathway in diabetes and hypergalactosemia.

Similar vascular pathological conditions are observed in diabetic animals and those with diet-induced hypergalactosemia. Both diabetes and hypergalactosemia are believed to cause vascular dysfunction via a common biochemical mechanism. In this study, we have found that both diabetes and hypergalactosemia in the short term (2-4 months) can increase total diacylglycerol (DAG) levels by 52 +/- 9 and 74 +/- 13% in the retina and aorta, respectively, of diabetic dogs, and by 94 +/- 9 and 78 +/- 11% in the retina and aorta, respectively, in dogs with hypergalactosemia as compared with normal control animals (P < 0.

Abnormalities of retinal metabolism in diabetes or galactosemia: ATPases and glutathione.

Purpose: Experimental galactosemia and diabetes are known to result in diabetic-like retinopathy in animals, but the mechanism by which the retinopathy develops remains unclear. Defects of retinal metabolism that are common to galactosemia and diabetes are closely associated with the development of retinopathy and might play a role in the pathogenesis of the retinal disease.

Methods: Effects of experimental galactosemia on retinal calcium-activated ATPase [(Ca,Mg)-ATPase], sodium-potassium ATPase [(Na,K)-ATPase], glutathione, ATP, and pertinent ions have been compared with the effects of experimental diabetes in rat and dog models of diabetic retinopathy.

Nerve conduction and aldose reductase inhibition during 5 years of diabetes or galactosaemia in dogs.

To evaluate the role of excessive polyol pathway activity in the pathogenesis of nerve disorders in diabetes mellitus, nerve conduction velocity was measured in motor nerves of diabetic dogs given an aldose reductase inhibitor (Sorbinil) or placebo, and also in non-diabetic dogs made experimentally galactosaemic. The nerve conduction velocity slowly declined in the diabetic placebo group, becoming significantly less than normal by the fifth year of the study, and the decline was prevented by administration of the aldose reductase inhibitor. Non-diabetic dogs made galactosaemic by consuming a 30% galactose diet developed erythrocyte and nerve polyol concentrations many times greater than that of diabetic or normal animals, but the nerve conduction velocity remained normal throughout 5 years of study.

Capillary basement membrane in retina, kidney, and muscle of diabetic dogs and galactosemic dogs and its response to 5 years aldose reductase inhibition.

Capillary basement membrane thickening has been compared in retina, renal glomerulus, and leg muscle of dogs alloxan-diabetic 5 years and dogs experimentally galactosemic 5 years, and the effects of inhibition of aldose reductase have been examined. Basement membrane in each site became thickened as a result of either galactosemia or diabetes, but showed appreciable variation among the sites. The thickening of basement membrane in retina and muscle of galactosemic animals was similar in quantity and appearance to that seen in the diabetics, notwithstanding large differences between the two animal models with respect to tissue polyol concentrations and nonenzymatic glycation of hemoglobin and plasma protein.

Aldose reductase inhibition fails to prevent retinopathy in diabetic and galactosemic dogs.

To investigate a possible role of excessive polyol production in the pathogenesis of diabetic retinopathy, 16 ALX-induced diabetic dogs and 20 experimentally galactosemic dogs were randomly assigned to 5 yr of treatment with either sorbinil, an aldose reductase inhibitor, or a placebo. The severity of hyperglycemia in sorbinil-treated and placebo groups was monitored throughout the 5-yr study by assay of glycosuria and nonenzymatically glycated plasma protein and HbA1 needed in an effort to avoid confounding possible group differences in hyperglycemia severity with possible drug effects. Inhibition of polyol production by sorbinil was monitored in erythrocytes throughout the study and also in retina and other tissue obtained at autopsy.