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  • 1
    ISSN: 1432-0428
    Keywords: Key words Diabetic retinopathy ; rat model ; aminoguanidine ; glycation ; retinal basement membrane.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have previously shown that long-term administration of aminoguanidine, an inhibitor of advanced glycosylation product formation, reduces the extent of experimental diabetic retinopathy in the rat by 85 %. In order to determine whether the residual retinopathy that developed despite aminoguanidine was attributable to advanced glycation endproduct formation, a time-course study was performed in three different groups of male Wistar rats: non-diabetic controls (NC), streptozotocin-diabetic controls (DC) and streptozotocin-diabetic rats treated with aminoguanidine HCL, 50 mg/100 ml drinking water (D-AG). Eyes were obtained at 24, 32, 44 and 56 weeks of diabetes/treatment duration and morphologic evaluation was done on retinal digest preparations. At 56 weeks, retinal basement membrane thickness was additionally measured. After 24 weeks of diabetes, the number of acellular capillaries was significantly elevated in DC (44.6 ± 5.7/mm2 of retinal area, NC 19.6 ± 4.9; p 〈 0.001) and increased continuously over time (DC 56 weeks 87.4 ± 15.1; p 〈 0.001 vs DC 24 weeks). In contrast, acellular capillaries in D-AG increased over the first 24 weeks and then remained constant for the rest of the study (D-AG 24 weeks 35.7 ± 5.18; p 〈 0.01 vs NC 24 weeks and NS vs DC 24 weeks; D-AG 56 weeks 42.0 ± 6.20; p NS vs D-AG 24 weeks). Diabetes-associated pericyte loss (DC 24 weeks 2310 ± 170/mm2 of capillary area; NC 24 weeks 3120 ± 190; p 〈 0.001; DC 56 weeks 1570 ± 230; NC 56 weeks 2960 ± 50; p 〈 0.001) was significantly prevented by aminoguanidine after diabetic-like changes over the initial 24 weeks (D-AG 24 weeks 2450 ± 75; p NS vs DC 24 weeks; D-AG 56 weeks 2350 ± 90; p 〈 0.001 vs DC 56 weeks). At 56 weeks, aminoguanidine treatment was associated with a 67.4 % reduction in retinal basement membrane thickening. This time-course study demonstrates that aminoguanidine prevents the progression of experimental diabetic retinopathy, and suggests that non AG-inhibitable mechanisms are involved in the initial phase of diabetic retinopathy. [Diabetologia (1995) 38: 269–273]
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Keywords Oxidant stress ; nicanartine ; diabetic retinopathy ; rat ; experimental.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to study the contribution of oxidant stress to the pathogenesis of experimental diabetic retinopathy, male streptozotocin diabetic Lewis rats were treated with the antioxidant and lipid-lowering compound nicanartine (80 mg/kg; n = 8, blood glucose level 16.7 ± 3.9 mmol/l; HbA1 11.8 ± 1.6 %) by oral supplementation for 6 months and compared with untreated diabetic (n = 6; blood glucose 18.1 ± 1.4 mmol/l; HbA1 11.5 ± 1.5 %) and untreated, non-diabetic rats (n = 8; blood glucose 4.0 ± 0.6 mmol/l; HbA1 4.8 ± 0.9 %). Diabetic retinopathy was evaluated by computer-assisted quantitative morphometry including measurement of autofluorescent advanced glycated end-products and immunohistochemistry for heme oxygenase I. Antioxidant treatment did not inhibit the 3.1-fold increase of retinal advanced glycation end products, while the expression of heme oxygenase I in both vascular and glial structures was markedly reduced. Chronic hyperglycaemia led to a 37.3 % increase in endothelial cells (p 〈 0.001 vs normal controls) and a 26.6 % reduction in pericyte numbers (p 〈 0.001 vs controls). Both abnormalities were significantly ameliorated by nicanartine (p 〈 0.001 vs diabetic controls). No effect was observed on the formation of acellular capillaries or microaneurysms. These data indicate that antioxidant therapy with nicanartine is of limited benefit in diabetic retinopathy, at least in the rodent model of streptozotocin-induced diabetes. [Diabetologia (1997) 40: 629–634]
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Diabetic retinopathy ; rat model ; hypertension ; SHR ; aminoguanidine ; glycation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Arterial hypertension has been identified as a major secondary risk factor for diabetic retinopathy. However, the mechanisms by which hypertension worsens retinopathy are unknown. Inhibition of advanced glycation product formation prevents the development of experimental diabetic retinopathy in normotensive diabetic rats. In this study the effect of hypertension on the rate of diabetic retinopathy development and the formation of arteriolar thrombosis was evaluated. We also evaluated the effect of aminoguanidine, an inhibitor of advanced glycation end product formation on retinal pathology of diabetic hypertensive rats. After 26 weeks of diabetes, hypertension accelerated the development of retinopathy despite a lower mean blood glucose level than in the non-hypertensive group (diabetic spontaneous hypertensive rats (SHR) 16.00±6.83 mmol/l; diabetic normotensive Wistar Kyoto rats (WKY) 34.9±3.64 mmol/l; p〈0.0001). Diabetic SHR had nearly twice as many acellular capillaries as diabetic WKY (SHR diabetic: 91.9±7.5 acellular capillaries per mm2 of retinal area vs WKY diabetic: 53.7±8.5 acellular capillaries per mm2 of retinal area), and a 3.8-fold increase in the number of arteriolar microthromboses (SHR diabetic 23504±5523 μm2 vs SHR non-diabetic 6228±2707 μm2). Aminoguanidine treatment of SHR diabetic rats reduced the number of acellular capillaries by 50%, and completely prevented both arteriolar deposition of PAS-positive material and abnormal microthrombus formation. These data suggest that hypertension-induced deposition of glycated proteins in the retinal vasculature plays a central role in the acceleration of diabetic retinopathy by hypertension.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0428
    Keywords: Diabetic retinopathy ; rat model ; aminoguanidine ; glycation ; retinal basement membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have previously shown that long-term administration of aminoguanidine, an inhibitor of advanced glycosylation product formation, reduces the extent of experimental diabetic retinopathy in the rat by 85%. In order to determine whether the residual retinopathy that developed despite aminoguanidine was attributable to advanced glycation endproduct formation, a time-course study was performed in three different groups of male Wistar rats: non-diabetic controls (NC), streptozotocin-diabetic controls (DC) and streptozotocin-diabetic rats treated with aminoguanidine HCL, 50 mg/100 ml drinking water (D-AG). Eyes were obtained at 24, 32, 44 and 56 weeks of diabetes/treatment duration and morphologic evaluation was done on retinal digest preparations. At 56 weeks, retinal basement membrane thickness was additionally measured. After 24 weeks of diabetes, the number of acellular capillaries was significantly elevated in DC (44.6±5.7/mm2 of retinal area, NC 19.6±4.9; p〈0.001) and increased continuously over time (DC 56 weeks 87.4±15.1; p〈0.001 vs DC 24 weeks). In contrast, acellular capillaries in D-AG increased over the first 24 weeks and then remained constant for the rest of the study (D-AG 24 weeks 35.7±5.18; p〈0.01 vs NC 24 weeks and NS vs DC 24 weeks; D-AG 56 weeks 42.0±6.20; p NS vs D-AG 24 weeks). Diabetes-associated pericyte loss (DC 24 weeks 2310±170/mm2 of capillary area; NC 24 weeks 3120±190; p〈0.001; DC 56 weeks 1570±230; NC 56 weeks 2960±50; p〈0.001) was significantly prevented by aminoguanidine after diabetic-like changes over the initial 24 weeks (D-AG 24 weeks 2450±75; p NS vs DC 24 weeks; D-AG 56 weeks 2350±90; p〈0.001 vs DC 56 weeks). At 56 weeks, aminoguanidine treatment was associated with a 67.4% reduction in retinal basement membrane thickening. This time-course study demonstrates that aminoguanidine prevents the progression of experimental diabetic retinopathy, and suggests that non AG-inhibitable mechanisms are involved in the initial phase of diabetic retinopathy.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0428
    Keywords: Diabetic retinopathy ; rat model ; aminoguanidine ; glycation ; secondary intervention ; islet transplantation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Primary prevention with aminoguanidine — an inhibitor of advanced glycation end product (AGE) formation — has been successfully employed to prevent diabetic retinopathy in the rat. However, it is unknown whether inhibition of AGE formation is still effective in a secondary intervention strategy. The present study addresses this question by comparing secondary intervention with aminoguanidine with syngeneic islet transplantation in the rat model. After 6 months of diabetes, one group was treated with aminoguanidine (50 mg/100 ml drinking water; D-AG) while another group received syngeneic transplantation of collagenase-ficoll isolated islets by intraportal injection (Tx). After an additional 4 months, both groups were compared to a normal (NC 10) and diabetic (DC 10) control group. Retinal autofluorescence was increased 2.5-fold after 6 months and increased 3.7-fold after 10 months of diabetes (p〈0.001). Aminoguanidine and islet Tx retarded the further accumulation of autofluorescence equally (p〈0.001 vs DC 10), although the values were higher than those observed in DC at 6 months (p〈0.001). Diabetes was associated with a 2.7-fold increase in acellular capillaries after 6 months and a 4.1-fold increase after 10 months. Treatment with aminoguanidine or islet Tx reduced but did not completely attenuate the progression of vascular occlusion (p〈0.001 vs DC 10; D-AG vs DC 6, p〈0.05; Tx vs DC 6, p〈0.01). Both treatments reduced endothelial proliferation (22.4% after 10 months; p〈0.001) and completely arrested pericyte dropout (40% after 10 months; p〈0.001). These data demonstrate that aminoguanidine is as effective as islet transplantation in retarding the progression of diabetic retinopathy in a secondary prevention setting.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0428
    Keywords: Keywords Diabetic retinopathy ; chinese hamster ; advanced-glycation end-products ; pericytes.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To assess the relationship between glucose and advanced glycation end products (AGE) and the relationship between AGE and retinal changes in vivo, we studied the time course of retinopathy over 12 months in trypsin digest preparations and measured glycaemia and retinal AGE in spontaneous diabetic hamsters of mild (MD) and severe (SD) phenotypes. Blood glucose levels were elevated in MD (9.44 ± 0.76 mmol/l) and in SD (3 months: 24.3 ± 1.4 mmol/l; 12 months: 31.7 ± 0.8 mmol/l) over non-diabetic controls (NC: 7.15 ± 0.25 mmol/l; p 〈 0.05 or less vs MD; p 〈 0.001 vs SD). Similar relations were found for HbA1. Retinal AGE in mild diabetes was 405 ± 11.3 arbitrary units (AU) (NC 245 ± 7.7; p 〈 0.01) after 3 months and remained unchanged. A non-linear increase of AGE over time was found in severe hyperglycaemic hamsters (466 ± 21 AU after 3 months and 758 ± 21 AU after 12 months; p 〈 0.001 vs MD). Pericyte loss in mild diabetes progressed from –26 % after 3 months to –41 % after 12 months (p 〈 0.001 vs NC). Whereas the initial pericyte loss in severely diabetic hamsters was identical to the mildly diabetic group, a higher degree of pericyte loss occurred after 12 months (–57 %; p 〈 0.05 vs MD). Endothelial cell numbers remained unaffected by mild hyperglycaemia, but significantly increased over time in severe diabetes reaching 31.7 % above controls after 12 months (p 〈 0.001 vs NC and MD). Microaneurysms were absent in all retinae examined. Acellular capillary segments were increased in mild diabetes (3.83 ± 0.31 per mm2 of retinal area) and severe diabetes (7.83 ± 0.73) over controls (1.0 ± 0.23). These data suggest that a threshold of glycaemia might exist above which AGE removal systems become saturated. Pericyte loss and acellular capillary formation are associated with mild increases in blood glucose and AGE levels while endothelial cell proliferation requires higher glucose and AGE levels. [Diabetologia (1998) 41: 165–170]
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0428
    Keywords: Keywords Diabetes, angiostatin, VEGF, bFGF, angiogenesis, retinopathy, cytokine, growth factors, photocoagulation, retina.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aims/hypothesis. Proliferative diabetic retinopathy is a major debilitating disease causing most cases of blindness in humans in the Western world. Photocoagulation is the established therapy of proliferative diabetic retinopathy, although the molecular mechanisms of its effects are still not known. Recently angiostatin has been characterized as a potent inhibitor of neovascularization. Apart from a possible down-regulation of angiogenic cytokines, release of angiostatin could initiate the anti-angiogenic effects of retinal photocoagulation.¶Methods. We investigated the regulation of angiostatin and the angiogenic cytokines vascular endothelial growth factor and basic fibroblast growth factor in vivo by comparing vitreal concentrations of 18 control patients and 34 patients with proliferative diabetic retinopathy with and without previous photocoagulation. Concentrations of basic fibroblast growth factor and angiostatin were additionally measured in serum, while vascular endothelial growth factor is known to be regulated locally in the eye. Cytokines were measured by immunological methods.¶Results. Angiostatin could be detected in 2 out of 18 control patients and in 25 out of 34 diabetic patients (p 〈 0.00 001). Most importantly, production of angiostatin in human vitreous correlated significantly with previous retinal photocoagulation (p 〈 0.0001) in patients with proliferative diabetic retinopathy. Only two patients (one control and one diabetic) had detectable serum concentrations of angiostatin. Additionally patients with proliferative diabetic retinopathy and with previous photocoagulation had significantly lower concentrations of vascular endothelial growth factor (0.9 ± 0.1 ng/ml; p 〈 0.0001) than diabetic patients without previous photocoagulation (4.0 ± 0.8 ng/ml). The investigation of vitreal and serum basic fibroblast growth factor concentrations yielded no significant differences between the groups.¶Conclusion/interpretation. Angiostatin is not a regularly expressed angiogenesis inhibitor in human vitreous. The alterations we observed suggest that local release of angiostatin and down-regulation of vascular endothelial growth factor mediate the therapeutic effects of retinal photocoagulation in proliferative diabetic retinopathy. [Diabetologia (2000) 43: 1404–1407]
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0428
    Keywords: Diabetic retinopathy ; rat model ; omega-3 fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Omega-3 fatty acids exert several important biological effects on factors that may predispose to diabetic retinopathy. Potential pathogenetic mechanisms include platelet dysfunction, altered eicosanoid production, increased blood viscosity in association with impaired cell deformability and pathologic leucocyte/endothelium interaction. Therefore, we tested whether a 6-month administration of fish oil (750 mg Maxepa, 5 times per week), containing 14% eicosapentaenoic acid (EPA) and 10% docosahexaenic acid, could inhibit the development of experimental retinopathy of the streptozotocin-diabetic rat. The efficiency of fish oil supplementation was evaluated by measuring EPA concentrations in total, plasma and membrane fatty acids and by measuring the generation of lipid mediators (leukotrienes and thromboxanes). Retinal digest preparations were quantitatively analysed for pericyte loss, and the formation of acellular capillaries. Omega-3 fatty acid administration to diabetic rats resulted in a twofold increase of EPA 20∶5 in total fatty acids, and a reduction of the thromboxane2/3 ratio from 600 (untreated diabetic rats) to 50 (treated diabetic rats). Despite these biochemical changes, diabetes-associated pericyte loss remained unaffected and the formation of acellular, occluded capillaries was increased by 75% in the fish oil treated diabetic group (115.1±26.8; untreated diabetic 65.2±15.0 acellular capillary segments/mm2 of retinal area). We conclude from this study that dietary fish oil supplementation may be harmful for the diabetic microvasculature in the retina.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0428
    Keywords: Key words Diabetic retinopathy, rat model, hypertension, SHR, aminoguanidine, glycation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Arterial hypertension has been identified as a major secondary risk factor for diabetic retinopathy. However, the mechanisms by which hypertension worsens retinopathy are unknown. Inhibition of advanced glycation product formation prevents the development of experimental diabetic retinopathy in normotensive diabetic rats. In this study the effect of hypertension on the rate of diabetic retinopathy development and the formation of arteriolar thrombosis was evaluated. We also evaluated the effect of aminoguanidine, an inhibitor of advanced glycation end product formation on retinal pathology of diabetic hypertensive rats. After 26 weeks of diabetes, hypertension accelerated the development of retinopathy despite a lower mean blood glucose level than in the non-hypertensive group (diabetic spontaneous hypertensive rats (SHR) 16.00±6.83 mmol/l; diabetic normotensive Wistar Kyoto rats (WKY) 34.9±3.64 mmol/l; p〈0.0001). Diabetic SHR had nearly twice as many acellular capillaries as diabetic WKY (SHR diabetic: 91.9±7.5 acellular capillaries per mm2 of retinal area vs WKY diabetic: 53.7±8.5 acellular capillaries per mm2 of retinal area), and a 3.8-fold increase in the number of arteriolar microthromboses (SHR diabetic 23 504± 5523 µm2 vs SHR non-diabetic 6228±2707 µm2). Aminoguanidine treatment of SHR diabetic rats reduced the number of acellular capillaries by 50 %, and completely prevented both arteriolar deposition of PAS-positive material and abnormal microthrombus formation. These data suggest that hypertension-induced deposition of glycated proteins in the retinal vasculature plays a central role in the acceleration of diabetic retinopathy by hypertension. [Diabetologia (1994) 37: 32–35]
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1432-0428
    Keywords: Key words Diabetic retinopathy ; rat model ; aminoguanidine ; glycation ; secondary intervention ; islet transplantation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Primary prevention with aminoguanidine – an inhibitor of advanced glycation end product (AGE) formation – has been successfully employed to prevent diabetic retinopathy in the rat. However, it is unknown whether inhibition of AGE formation is still effective in a secondary intervention strategy. The present study addresses this question by comparing secondary intervention with aminoguanidine with syngeneic islet transplantation in the rat model. After 6 months of diabetes, one group was treated with aminoguanidine (50 mg/100 ml drinking water; D-AG) while another group received syngeneic transplantation of collagenase-ficoll isolated islets by intraportal injection (Tx). After an additional 4 months, both groups were compared to a normal (NC 10) and diabetic (DC 10) control group. Retinal autofluorescence was increased 2.5-fold after 6 months and increased 3.7-fold after 10 months of diabetes (p 〈 0.001). Aminoguanidine and islet Tx retarded the further accumulation of autofluorescence equally (p 〈 0.001 vs DC 10), although the values were higher than those observed in DC at 6 months (p 〈 0.001). Diabetes was associated with a 2.7-fold increase in acellular capillaries after 6 months and a 4.1-fold increase after 10 months. Treatment with aminoguanidine or islet Tx reduced but did not completely attenuate the progression of vascular occlusion (p 〈 0.001 vs DC 10; D-AG vs DC 6, p 〈 0.05; Tx vs DC 6, p 〈 0.01). Both treatments reduced endothelial proliferation (22.4 % after 10 months; p 〈 0.001) and completely arrested pericyte dropout (40 % after 10 months; p 〈 0.001). These data demonstrate that aminoguanidine is as effective as islet transplantation in retarding the progression of diabetic retinopathy in a secondary prevention setting. [Diabetologia (1995) 38: 656–660]
    Type of Medium: Electronic Resource
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