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R L Engerman

Publications and source records attributed to R L Engerman.

At least 19 recordsLinked to original sources
PubMed1997

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. Administration of supplemental antioxidants, vitamins C and E, for the 2 months prevented the diabetes-induced impairment of antioxidant defense system in the retina. In experimentally galactosemic rats, the supplemental antioxidants were not as effective: SOD activity was normalized, but the enzymes of the glutathione redox cycle were only partly restored, and the subnormal catalase activity was unaffected. Diabetes or experimental galactosemia results in significant impairment of the antioxidant defense system in the retina, and exogenous antioxidant supplementation can help alleviate the subnormal activities of antioxidant defense enzymes.

Animals↗
PubMed1996

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. These lesions never were seen in cerebral cortical vessels of the same animals. The only morphologic abnormality observed in cerebral capillaries of dogs with diabetes and dogs fed galactose was thickening of basement membrane. CONCLUSIONS: Local influences in the eye apparently play an important role in the development of diabetic retinopathy. Current hypotheses about the pathogenesis of the retinopathy do not account adequately for such differences in the tissue distribution of vascular lesions.

Animals↗
PubMed1996

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. In C57BL/6 mice fed 30% galactose for 21 to 26 months, saccular microaneurysms were observed in the retina, together with significant increases in the thickness of capillary basement membrane and the prevalence of acellular capillaries and pericyte ghosts. The 50% galactose diet caused significantly more acellular capillaries than normal by 15 months, but excessive mortality precluded study at longer durations. The frequency of acellular capillaries also was greater than normal in BALB/c mice fed 30% galactose for 21 months. Retinal polyol levels in galactose-fed mice were found to be lower than those in galactosemic rats. CONCLUSION: The mouse may provide an inexpensive model suitable for in vivo study of the pathogenesis of diabetic retinopathy using molecular biological techniques.

Aneurysm↗
PubMed1996

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. Mean levels of collagen digestibility by pepsin decreased (NS) whereas collagen glycation (P < 0.001), pentosidine cross-links (P < 0.001), and collagen fluorescence (P = 0.02) increased with increasing mean HbA1 values. Similarly, mean levels of lens crystallin glycation (P < 0.001), fluorescence (P < 0.001), and the specific advanced lens Maillard product 1 (LM-1) (P < 0.001) and pentosidine (P < 0.005) increased significantly with poorer glycemic control. Statistical analysis revealed very high Spearman correlation coefficients between collagen and lens changes. Whereas pentosidine cross-links were significantly elevated in collagen from diabetic dogs with moderate levels of HbA1 (i.e., 8.0 +/- 0.4%), lens pentosidine levels were normal in this group and were elevated (P < 0.001) only in the animals with poor glycemic control (HbA1 = 9.7 +/- 0.6%). Thus, whereas protein glycation and advanced glycation in the extracellular matrix and in the lens are generally related to the level of glycemic control, there is evidence for a tissue-specific glycemic threshold for pentosidine formation, i.e., glycoxidation, in the lens. This threshold may be in part linked to a dramatic acceleration in crystallin glycation with HbA1 values of > 8.0% and/or a loss of lens membrane permeability. This study provides support at the molecular level for the growing concept that glycemic thresholds may be involved in the development of some of the complications in diabetes.

Animals↗
PubMed1996

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. In diabetic rats, TBARS were elevated by 74% in retina and 87% in plasma. In galactose-fed rats, TBARS were significantly elevated in retina (P < 0.05), but were normal in plasma. The administration of supplemental dietary ascorbic acid and alpha-tocopherol acetate for 2 months prevented the elevation of retinal TBARS and the decrease of Na(+)-K(+)-ATPase and calcium ATPase activities in retinas of diabetic animals without having any beneficial effect on plasma TBARS. In galactosemic rats, these antioxidants had a partial beneficial effect on the activity of retinal Na(+)-K(+)-ATPase, but failed to have any effect on calcium ATPase. The beneficial effects of antioxidants in diabetes and experimental galactosemia were not caused by the amelioration of hyperglycemia or retinal polyol accumulation. Erythrocyte osmotic fragility was increased by more than twofold in diabetes, but was normal in experimental galactosemia, and antioxidants prevented diabetes-induced increases in erythrocyte osmotic fragility-Diabetes-induced increased oxidative stress and subnormal ATPase activities in the retina can be inhibited by dietary supplementation with antioxidants.

Animals↗
PubMed1995

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. At the end of 24 months, the dogs were divided into two groups, one of which continued to receive the galactose diet, while the second immediately began receiving the diet minus galactose. All animals were killed after 60 months of study. RESULTS: Consumption of the galactose-rich diet resulted, as expected, in galactosemia evident by elevated hemoglobin A1, plasma nonenzymatically glycated protein, and erythrocyte polyol concentrations, each of which decreased to normal levels following withdrawal of dietary galactose. Retinopathy was found to be equivocal at the end of 24 months of the galactose diet and subsequently progressed significantly despite cessation of the galactose diet. CONCLUSION: The fact that retinopathy did not halt promptly at intervention is consistent with previous data from diabetic dogs and suggests that the vascular lesions may be due to sequelae of excessive tissue aldohexose that are not promptly corrected by correction of the aldohexose level.

Animals↗
PubMed1995

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. Numbers of lesions were expressed relative to area of trypsin-digested retina examined or to total number of capillary cells examined. Microaneurysms and acellular capillaries were not uniformly distributed across the retina in diabetes or in galactosemia, both lesions being significantly (more than two-fold) more prevalent in the superior temporal retina than in the inferior nasal quadrant of retina. In contrast, the distribution of pericyte ghosts in these same eyes was not significantly different between the quadrants. These findings suggest that pericyte loss may not be sufficient to account for the development of microaneurysms and acellular (occluded) capillaries in diabetes, and raise a possibility that the lesions occur by different mechanisms. Currently available hypotheses regarding the pathogenesis of diabetic retinopathy fail to account for regional differences in the distribution of the vascular lesions within the same retina. Local factors within the eye apparently play an important role in the response of the retinal microvasculature to hyperglycemia.

Animals↗
PubMed1995

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. Similar lesions were observed in rats receiving a 30% galactose diet for 23 months. Capillary basement membrane thickening, dilated hypercellular capillaries (or intra-retinal microvascular abnormalities), and foci of vascular cells appeared in rats fed 50% galactose, but saccular microaneurysms characteristic of retinopathy in diabetic patients, diabetic dogs, and experimentally galactosemic dogs were not observed. Administration of the aldose reductase inhibitor, Sorbinil, to rats fed 50% galactose resulted in a significant inhibition of cataract and of galactitol accumulation in nerve and blood (by more that 90%) and retina (by 62%), but did not inhibit development of the retinal microvascular lesions. CONCLUSIONS: Two years of galactosemia in rats seems to reproduce only a portion of the lesions characteristic of diabetic retinopathy in patients or dogs. Nevertheless, lesions characteristic of at least the early stages of retinopathy clearly do develop in this galactosemic rat model, and are not restrained by inhibition of retinal polyol accumulation by 62%.

Aldehyde Reductase↗
PubMed1994

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. These results in dogs suggest that aldose reductase inhibitors may prevent defective nerve conduction in long-term diabetes, and raise the possibility that excessive accumulation of polyol itself is not sufficient to produce the nerve defect in the absence of excessive polyol utilization.

Aldehyde Reductase↗
PubMed1994

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 < 0.01). The elevation of DAG levels was maintained for 5 years in the aortas of diabetic and hypergalactosemic dogs. To characterize the mechanism of the DAG increases, we have determined that total DAG levels were significantly increased in cultured macro- and microvascular cells exposed to elevated glucose (22 mM) and galactose (16.5 mM) levels. These increased levels were not prevented by sorbinil, an aldose reductase inhibitor. One of the sources of the increased DAG levels was probably derived from de novo synthesis from both hexoses as determined by radiolabeling studies. Intracellularly, the DAG elevation activated protein kinase C (PKC) activity with increases of 58 +/- 12% (P < 0.05) and 66 +/- 8% (P < 0.01) in the membrane fraction of cultured aortic smooth muscle cells exposed to elevated glucose and galactose levels, respectively. These findings have clearly demonstrated a possible common biochemical mechanism by which hyperglycemia and hypergalactosemia can chronically activate the DAG-PKC pathway in the vasculature and could be a possible explanation for the development of diabetic vascular complications.

Animals↗
PubMed1994

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). Rats fed 50% galactose showed greater than normal frequency of retinal pericyte ghosts and acellular capillaries, and thickening of capillary basement membranes by 18 months of galactosemia. Rats eating 30% galactose developed similar retinal lesions, and tended to be healthier than rats fed 50% galactose. Diabetes of 1 1/4 years or more likewise resulted in retinal pericyte ghosts, acellular capillaries and thickened capillary basement membrane. IRMAs and other vascular abnormalities were not reproducibly demonstrated at this duration of study, and saccular microaneurysms were not seen in any groups. In a number of diabetic rats, the severity of diabetes diminished spontaneously (after 1 to 1 1/2 years of insulin deficiency), thus making it essential that glycemia be systematically monitored. Both diabetic rats and experimentally galactosemic rats develop microvascular lesions that are consistent with at least the early stages of diabetic retinopathy, and these models should be useful to screen potential therapies for their ability to inhibit the development of retinopathy.

Alloxan↗
PubMed1994

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. In contrast, cerebral cortex from the same diabetic rats and galactosemic rats showed no significant reduction in either gamma-glutamyl transpeptidase activity or glutathione level. These different responses of the two tissues to hyperglycemia might help account for the difference in microvascular disease in these two tissues in diabetes. Consumption of the antioxidants, ascorbic acid (1.0%) plus alpha-tocopherol (0.1%), by diabetic rats and galactosemic rats inhibited the decrease of gamma-glutamyl transpeptidase activity and glutathione levels in retina, suggesting that defects in glutathione regulation in the retina are secondary to hyperglycemia-induced 'oxidative stress'.

Animals↗
PubMed1994

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. RESULTS: Activities of (Ca,Mg)-ATPase and (Na,K)-ATPase were decreased as a result of either experimental galactosemia or diabetes in both the dog and the rat, and the decreases were accompanied by a diminution of reduced glutathione (GSH) in the retina. Ouabain-insensitive ATPase activity in the retina was not significantly reduced by diabetes or galactosemia, suggesting that the observed defects in (Ca,Mg)-ATPase and (Na,K)-ATPase activities were specific. The decrease of retinal GSH levels was associated with an elevated concentration of oxidized glutathione in diabetes but not in galactosemia. Retinal ATP and ion concentrations remained unaffected by experimental galactosemia or diabetes. CONCLUSIONS: Comparison of two etiologically dissimilar models of diabetic retinopathy (diabetes and galactosemia) has revealed abnormalities of retinal metabolism that are shared by the two models. Further comparisons of retinal metabolism between these two models should reveal additional sequelae of hyperglycemia that are associated with, and that might play a role in, the development of diabetic retinopathy.

Adenosine Triphosphate↗
PubMed1993

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. Trypsin digests of retinal vessels were compared after 60 mo of diabetes and after 42 and 60 mo of galactosemia. In diabetic dogs, development of retinopathy was not significantly influenced by a sorbinil dose (20 mg.kg-1 x day-1) sufficient to prevent elevation of sorbitol levels in retina and other tissue. Likewise, in dogs made experimentally galactosemic for 42-60 mo, administration of sorbinil (60-80 mg.kg-1 x day-1) had no significant effect on the development of retinopathy notwithstanding prevention of 93-96% of the polyol elevation in retina and other tissue. Retinal capillary basement membrane was significantly thicker than normal in diabetic and in galactosemic dogs and was not significantly influenced by administration of sorbinil in either dog model. Thus, no evidence was found that the development of retinopathy is critically dependent on excessive polyol production or accumulation.

Aldehyde Reductase↗
PubMed1991

Renal hemodynamics in experimentally galactosemic dogs and diabetic dogs.

To examine the association between renal hemodynamic abnormalities and the development of diabetic kidney disease, glomerular filtration rate (GFR) and renal plasma flow (RPF) have been determined in dogs with alloxan-induced diabetes or experimental galactosemia of 1 to 5 years duration. GFR and RPF were significantly greater than normal in insulin-deficient diabetic dogs. GFR was also significantly greater than normal in the galactosemic animals, and RPF tended to be elevated even though GFR and RPF were measured at time of day when plasma galactose is no longer elevated. GFR and effective RPF (eRPF) were found to increase in normal animals upon acute elevation of blood galactose or glucose concentration. Thus, GFR is supranormal in experimental galactosemia, as well as in diabetes, although galactosemia has been shown not to cause nephromegaly, mesangial expansion, or glomerular obliteration, which are typical of diabetes. Administration of an aldose reductase inhibitor (Sorbinil) at dosages sufficient to significantly reduce erythrocyte polyol concentration did not significantly influence GFR or RPF in diabetic or galactosemic dogs.

Aldehyde Reductase↗
PubMed1991

Retinal polyol and myo-inositol in galactosemic dogs given an aldose-reductase inhibitor.

Galactitol and myo-inositol concentrations were measured in retinas, erythrocytes, and skeletal muscle of experimentally galactosemic dogs receiving a placebo or the aldose reductase inhibitor, sorbinil, for 5 yr. The concentration of galactitol was increased more than 30-fold in the retina and other tissues by galactosemia, and the increase was inhibited 90-96% in all tissues by sorbinil. The concentration of free myo-inositol was greater than normal in retinas of galactosemic dogs, and its concentration was not altered by the aldose-reductase inhibitor. The myo-inositol concentration likewise was greater than normal in the retinas of dogs that were diabetic for 2-4 months. The marked inhibition of polyol production and accumulation in the retina of sorbinil-treated galactosemic dogs was not associated with a comparable inhibition of retinopathy.

Aldehyde Reductase↗