Advanced glycation end products induce glomerular sclerosis and albuminuria in normal rats.

High levels of tissue advanced glycation end products (AGEs) that result from the spontaneous modification of proteins by glucose occur in diabetes and aging. To address the potential pathogenic role of AGEs in the glomerulosclerosis of diabetes or nephrosclerosis of aging, doses of AGE-modified rat albumin (25 mg per kg per day, i.v.) sufficient to elevate circulating AGE levels to the range of diabetic serum were administered daily to healthy rats alone or in combination with the AGE inhibitor aminoguanidine. After 5 months, the AGE content of renal tissues in AGE-treated rats rose to 50% above controls (P < 0.025), whereas serum contained 2.8-fold greater AGE levels (P < 0.025). Light and electron microscopy of kidneys from AGE-treated rats revealed a more than 50% increase in glomerular volume compared to controls (P < 0.001), significant periodic acid/Schiff reagent-positive deposits, basement membrane widening, and mesangial extracellular matrix increase and indicated significant glomerulosclerosis compared to untreated (P < 0.002) or albumin-treated controls (P < 0.002). These changes were associated with significant loss of protein (P < 0.005) and albumin (P < 0.002) in the urine of AGE-treated rats compared to controls. Cotreatment with aminoguanidine markedly limited both the structural and functional defects. These in vivo data demonstrate that AGEs influence glomerular structure and function in a manner leading to glomerulosclerosis. The effects are AGE-specific, as they are ameliorated by a pharmacological AGE inhibitor, aminoguanidine.     

Lipoprotein Modification by Advanced Glycosylation Endproducts (AGEs): Role in Atherosclerosis

Recent progress in our understanding of advanced glycosylation reactions in vivo has affirmed the hypothesis that these products play an important role in the evolution of both diabetic and nondiabetic vascular disease. Utilizing newly developed advanced glycosylation end-products (AGE)-specific enzyme-linked immunosorbent assay (ELISA) techniques, AGEs have been identified to be present on a variety of vascular wall, lipoprotein, and lipid constituents. Vascular wall AGEs contribute to vascular pathology by increasing vascular permeability, enhancing subintimal protein and lipoprotein deposition, and inactivating nitric oxide. Lipid-linked AGEs present in low-density lipoprotein (LDL) also have been shown to initiate oxidative modification, promoting oxidation reactions that may proceed without the involvement of free metals or other radical generating systems. AGE-specific ELISA analysis has demonstrated a significantly increased level of AGE-modified LDL in the plasma of diabetic patients when compared to normal controls. AGE-modification impairs LDL-receptor-mediated clearance mechanisms in vivo and may contribute to elevated LDL levels in patients with diabetes. This concept has been substantiated further by the recent clinical observations that administration of the advanced glycosylation inhibitor aminoguanidine to diabetic patients significantly decreases circulating LDL levels. (Trends Cardiovasc Med 1997;7:39-47). ? 1997, Elsevier Science Inc.     

Neurotoxicity of advanced glycation endproducts during focal stroke and neuroprotective effects of aminoguanidine.

Cerebral infarction (stroke) is a potentially disastrous complication of diabetes mellitus, principally because the extent of cortical loss is greater in diabetic patients than in nondiabetic patients. The etiology of this enhanced neurotoxicity is poorly understood. We hypothesized that advanced glycation endproducts (AGEs), which have previously been implicated in the development of other diabetic complications, might contribute to neurotoxicity and brain damage during ischemic stroke. Using a rat model of focal cerebral ischemia, we show that systemically administered AGE-modified bovine serum albumin (AGE-BSA) significantly increased cerebral infarct size. The neurotoxic effects of AGE-BSA administration were dose- and time-related and associated with a paradoxical increase in cerebral blood flow. Aminoguanidine, an inhibitor of AGE cross-linking, attenuated infarct volume in AGE-treated animals. We conclude that AGEs may contribute to the increased severity of stroke associated with diabetes and other conditions characterized by AGE accumulation.     

Advanced glycation end products and their receptors co-localise in rat organs susceptible to diabetic microvascular injury

Summary Advanced glycation end products (AGEs) are believed to play an important role in the development of diabetic complications. AGEs are increased in experimental diabetes and treatment with the inhibitor of advanced glycation end products, aminoguanidine, has been shown to attenuate the level of these products in tissues undergoing complications. Recently, an AGE-binding protein has been isolated from bovine lung endothelial cells and termed the receptor for advanced glycated end products (RAGE). The present study sought to determine the distribution of AGE and RAGE in tissues susceptible to the long-term complications of diabetes including the kidney, eye, nerve, arteries as well as in a tissue resistant to such complications, the lung. Using polyclonal antisera both AGE and RAGE were found to co-localize in the renal glomerulus. AGE staining was clearly increased with age and was further increased by diabetes. Aminoguanidine treatment reduced AGE accumulation in the kidney. Co-localisation of AGE and RAGE was demonstrated in the inner plexiform layer and the inner limiting membrane of the retina and in nerve bundles from mesenteric arteries. In the aorta, both AGE and RAGE were found in the intima, media and adventitia. Medial staining was increased in diabetes and was reduced by aminoguanidine treatment. A similar pattern was observed for RAGE in the aorta. In the lung, RAGE was found widely distributed throughout the lung whereas the distribution of AGE staining was more limited, primarily localising to macrophages. The co-localisation of AGEs and RAGE in sites of diabetic microvascular injury suggests that this ligand-receptor interaction may represent an important mechanism in the genesis of diabetic complications. [Diabetologia (1997) 40: 619–628] Received: 16 October 1996 and in final revised form: 17 February 1997     

糖尿病大鼠主动脉糖化终产物的免疫组化研究

目的　研究糖尿病时主动脉壁非酶糖化的程度以及非酶糖化机制在糖尿病血管重建和慢性并发症发生发展中的作用。方法　应用抗糖化终产物（ＡＧＥｓ） 多克隆抗体,对糖尿病大鼠和氨基胍治疗后的糖尿病大鼠进行主动脉壁ＡＧＥｓ 的免疫组化研究,计算机图像处理系统定量分析。结果糖尿病时主动脉壁中膜ＡＧＥｓ 的相对面积呈进行性增加,４ 周时其相对面积就显著大于对照组（ Ｐ＜０．０１）,氨基胍治疗４ 周后主动脉壁中膜ＡＧＥｓ 的相对面积较糖尿病组显著降低（ Ｐ＜ ０．０５）,治疗２４周后降低更为明显（Ｐ＜ ０．０１）。结论　主动脉壁ＡＧＥｓ 的免疫组化定量研究能更直观地反映血管组织非酶糖化的程度,非酶糖化是引起血管重建的重要机制之一。     

Cross-linking of glycated collagen in the pathogenesis of arterial and myocardial stiffening of aging and diabetes

The normal aging process is often accompanied by arterial wall stiffening and by a decrease in myocardial compliance. These processes contribute to isolated systolic hypertension and diastolic heart failure, which lead to substantial morbidity and mortality among older individuals. Patients with diabetes manifest arterial stiffening and diastolic dysfunction at a younger age. This leads to the concept that the mechanism that underlies changes in vascular mechanical properties during aging is accelerated in diabetes. The Maillard reaction or advanced glycation of proteins occurs slowly in vivo with normal aging and at an accelerated rate in diabetes. Advanced glycation end-products (AGEs) that form during the Maillard reaction are implicated in the complications of aging and diabetes. The formation of AGEs on vascular wall and myocardial collagen causes cross-linking of collagen molecules to each other. This leads to the loss of collagen elasticity, and subsequently a reduction in arterial and myocardial compliance. Aminoguanidine, an inhibitor of AGE formation, is effective in slowing or preventing arterial stiffening and myocardial diastolic dysfunction in aging and diabetic animals. In aged and diabetic animals, agents that can chemically break pre-existing cross-linking of collagen molecules are capable of reverting indices of vascular and myocardial compliance to levels seen in younger or non-diabetic animals. These studies suggest that collagen cross-linking is a major mechanism that governs aging and diabetes-associated loss of vascular and cardiac compliance. The development of AGEs cross-link breakers may have important role for future therapy of isolated systolic hypertension and diastolic heart failure in these conditions.     

橙皮苷对STZ糖尿病大鼠肾脏功能和形态的影响

观察橙皮苷对链脲佐菌素导致的糖尿病大鼠肾脏功能和形态的影响,并与氨基胍进行比较。结果表明:（1）两治疗组大鼠尿蛋白排泄量显著低于对照组P<0.05）;（2）两治疗组肾组织AGEs和LPO含量显著低于对照组（P<0.01,P<0.05）:（3）治疗组肾小球系膜增生和基底膜增厚明显减轻。提示橙皮苷在抑制蛋白非酶糖基化、预防糖尿病肾脏并发症方面具有与氨基胍相似的作用。     

Advanced glycation end products cause increased CCN family and extracellular matrix gene expression in the diabetic rodent retina

Aims/hypothesis Referred to as CCN, the family of growth factors consisting of cystein-rich protein 61 (CYR61, also known as CCN1), connective tissue growth factor (CTGF, also known as CCN2), nephroblastoma overexpressed gene (NOV, also known as CCN3) and WNT1-inducible signalling pathway proteins 1, 2 and 3 (WISP1, −2 and −3; also known as CCN4, −5 and −6) affects cellular growth, differentiation, adhesion and locomotion in wound repair, fibrotic disorders, inflammation and angiogenesis. AGEs formed in the diabetic milieu affect the same processes, leading to diabetic complications including diabetic retinopathy. We hypothesised that pathological effects of AGEs in the diabetic retina are a consequence of AGE-induced alterations in CCN family expression. Materials and methods CCN gene expression levels were studied at the mRNA and protein level in retinas of control and diabetic rats using real-time quantitative PCR, western blotting and immunohistochemistry at 6 and 12 weeks of streptozotocin-induced diabetes in the presence or absence of aminoguanidine, an AGE inhibitor. In addition, C57BL/6 mice were repeatedly injected with exogenously formed AGE to establish whether AGE modulate retinal CCN growth factors in vivo. Results After 6 weeks of diabetes, Cyr61 expression levels were increased more than threefold. At 12 weeks of diabetes, Ctgf expression levels were increased twofold. Treatment with aminoguanidine inhibited Cyr61 and Ctgf expression in diabetic rats, with reductions of 31 and 36%, respectively, compared with untreated animals. Western blotting showed a twofold increase in CTGF production, which was prevented by aminoguanidine treatment. In mice infused with exogenous AGE, Cyr61 expression increased fourfold and Ctgf expression increased twofold in the retina. Conclusions/interpretation CTGF and CYR61 are downstream effectors of AGE in the diabetic retina, implicating them as possible targets for future intervention strategies against the development of diabetic retinopathy. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Attenuation of hypertension development by aminoguanidine in spontaneously hypertensive rats: role of methylglyoxal

BACKGROUND: Methylglyoxal (MG), a metabolite of glucose, and MG-induced advanced glycation endproducts (AGEs) are causatively associated with vascular complications of diabetes mellitus. We have previously reported elevated levels of MG and MG-induced AGEs in spontaneously hypertensive rats (SHR). The purpose of this study was to investigate the causative role of MG and MG-induced AGEs in the pathogenesis of hypertension in SHR. METHODS: Young SHR were treated with an AGE inhibitor, aminoguanidine, for 9 weeks. HPLC was used to determine plasma and aortic MG and reduced glutathione levels. The MG-induced AGEs, N epsilon-carboxyethyl-lysine (CEL) and argpyramidine, in the aorta were determined by immunohistochemistry. Vascular relaxation of small mesenteric arteries was measured using myograph. RESULTS: Chronic treatment with aminoguanidine attenuated age-dependent blood pressure (BP) increase in SHR. Plasma and aortic MG levels, and aortic levels of MG-induced AGEs, were significantly reduced after aminoguanidine treatment, which were comparable to those from age-matched Wistar Kyoto rats. Free radical level was significantly lowered, whereas reduced glutathione level was significantly increased by aminoguanidine treatment in the aortic tissues from SHR. Moreover, aminoguanidine therapy prevented the morphologic damage of vascular tissues in SHR and restored the endothelium-dependent relaxation to acetylcholine. Chronic aminoguanidine treatment also increased aortic endothelial nitric oxide synthase expression and reduced inducible nitric oxide synthase expression. CONCLUSIONS: The MG and MG-induced AGEs contribute to the pathogenesis of hypertension by altering the redox balance, causing vascular eutrophic inward remodeling, and inducing endothelial dysfunction in SHR.     

Prevention of cardiovascular and renal pathology of aging by the advanced glycation inhibitor aminoguanidine.

Human aging is impacted severely by cardiovascular disease and significantly but less overtly by renal dysfunction. Advanced glycation endproducts (AGEs) have been linked to tissue damage in diabetes and aging, and the AGE inhibitor aminoguanidine (AG) has been shown to inhibit renal and vascular pathology in diabetic animals. In the present study, the effects of AG on aging-related renal and vascular changes and AGE accumulation were studied in nondiabetic female Sprague-Dawley (S-D) and Fischer 344 (F344) rats treated with AG (0.1% in drinking water) for 18 mo. Significant increases in the AGE content in aged cardiac (P < 0.05), aortic (P < 0.005), and renal (P < 0.05) tissues were prevented by AG treatment (P < 0.05 for each tissue). A marked age-linked vasodilatory impairment in response to acetylcholine and nitroglycerine was prevented by AG treatment (P < 0.005), as was an age-related cardiac hypertrophy evident in both strains (P < 0.05). While creatinine clearance was unaffected by aging in these studies, the AGE/ creatinine clearance ratio declined 3-fold in old rats vs. young rats (S-D, P < 0.05; F344, P < 0.01), while it declined significantly less in AG-treated old rats (P < 0.05). In S-D but not in F344 rats, a significant (P < 0.05) age-linked 24% nephron loss was completely prevented by AG treatment, and glomerular sclerosis was markedly suppressed (P < 0.01). Age-related albuminuria and proteinuria were markedly inhibited by AG in both strains (S-D, P < 0.01; F344, P < 0.01). These data suggest that early interference with AGE accumulation by AG treatment may impart significant protection against the progressive cardiovascular and renal decline afflicting the last decades of life.     

Aminoguanidine inhibits albuminuria, but not the formation of advanced glycation end-products in skin collagen of diabetic rats

Aminoguanidine, an inhibitor of advanced glycation reactions in vitro, inhibits the development of diabetic complications in animal models of diabetes, suggesting that it acts by inhibition of advanced glycation reactions in vivo. However, effects of aminoguanidine on the formation of specific advanced glycation end-products (AGEs) in vivo have not been rigorously examined. Therefore, we studied the effects of aminoguanidine on the formation of pentosidine and N(epsilon)-(carboxymethyl)lysine (CML), measured by analytical chemical methods, in collagen of streptozotocin-diabetic Lewis rats at doses which ameliorated urinary albumin excretion, an index of diabetic nephropathy. At 12 weeks, diabetic animals had fivefold higher blood glucose, threefold higher glycated hemoglobin and fivefold higher collagen glycation, compared to metabolically healthy controls; pentosidine and CML in skin collagen were increased by approximately 30 and 150%, respectively. Administration of aminoguanidine, 50 mg/kg by daily intraperitoneal injection, significantly inhibited the development of albuminuria (approximately 60%, P < 0.01) in diabetic rats, without an effect on blood glucose or glycation of hemoglobin or collagen. Surprisingly, aminoguanidine failed to inhibit the increase in pentosidine and CML in diabetic rat skin collagen. Similar results were obtained in an independent experiment in which aminoguanidine was administered in drinking water at a dose of 0.5 g/l. We conclude that the therapeutic benefits of aminoguanidine on albuminuria may not be the result of inhibition of AGE formation.     

Protein glycation: a firm link to endothelial cell dysfunction

The advanced glycation end products (AGEs) are a heterogeneous class of molecules, including the following main subgroups: bis(lysyl)imidazolium cross-links, hydroimidazolones, 3-deoxyglucosone derivatives, and monolysyl adducts. AGEs are increased in diabetes, renal failure, and aging. Microvascular lesions correlate with the accumulation of AGEs, as demonstrated in diabetic retinopathy or renal glomerulosclerosis. On endothelial cells, ligation of receptor for AGE (RAGE) by AGEs induces the expression of cell adhesion molecules, tissue factor, cytokines such as interleukin-6, and monocyte chemoattractant protein-1. A chief means by which AGEs via RAGE exert their effects is by generation of reactive oxygen species, at least in part via stimulation of NADPH oxidase. Diabetes-associated vascular dysfunction in vivo can be prevented by blockade of RAGE. Thus, agents that limit AGE formation, increase the catabolism of these species, or antagonize their binding to RAGE may provide new targets for vascular protection in diabetes.     

Relative contributions of advanced glycation and nitric oxide synthase inhibition to aminoguanidine-mediated renoprotection in diabetic rats

Summary Advanced glycation end products (AGEs) have previously been shown to be increased in the diabetic kidney. Aminoguanidine, an inhibitor of advanced glycation, has been shown to attenuate the development of AGEs as well as the progression of renal disease in experimental diabetes. However, the precise mechanisms through which aminoguanidine acts remain to be elucidated since it is also able to act as an inhibitor of nitric oxide synthase (NOS). This study has therefore compared the effects of aminoguanidine with the effects of two other inhibitors of NOS, L -NAME and methylguanidine, on the development of experimental diabetic nephropathy. Diabetic rats were randomised to receive no treatment, aminoguanidine (1 g/l in drinking water), L -NAME (5 mg/l in drinking water) or methylguanidine (1 g/l in drinking water). Diabetic rats had increased levels of albuminuria and urinary nitrite/nitrate excretion when compared to control rats. Renal AGEs measured by fluorescence as well as by a carboxymethyllysine reactive radioimmunoassay, were elevated in diabetic rats. No changes in inducible NOS (iNOS) protein expression were detected in experimental diabetes nor did aminoguanidine affect iNOS expression. Aminoguanidine did not affect blood glucose or HbA_1c but it did prevent increases in albuminuria, urinary nitrites/nitrates and renal AGE levels as measured by fluorescence and radioimmunoassay. L -NAME and methylguanidine did not retard the development of albuminuria, nor did they prevent increases in renal AGE levels, as assessed by fluorescence. However, these treatments did prevent increases in AGEs, as measured by radioimmunoassay. This study indicates that the renoprotective effect of aminoguanidine in experimental diabetes cannot be reproduced by L -NAME or methylguanidine. It is likely that the effect of aminoguanidine is mediated predominantly by decreased AGE formation rather than via NOS inhibition. It also raises the possibility that inhibition of fluorescent AGE formation may be more renoprotective than inhibition of the formation of carboxymethyllysine-containing AGEs. [Diabetologia (1997) 40: 1141–1151] Received: 10 April 1997 and in revised form: 18 June 1997     

Blockade of advanced glycation end-product formation restores ischemia-induced angiogenesis in diabetic mice

We hypothesized that formation of advanced glycation end products (AGEs) associated with diabetes reduces matrix degradation by metalloproteinases (MMPs) and contributes to the impairment of ischemia-induced angiogenesis. Mice were treated or not with streptozotocin (40 mg/kg) and streptozotocin plus aminoguanidine (AGEs formation blocker, 50 mg/kg). After 8 weeks of treatment, hindlimb ischemia was induced by right femoral artery ligature. Plasma AGE levels were strongly elevated in diabetic mice when compared with control mice (579 +/- 21 versus 47 +/- 4 pmol/ml, respectively; P < 0.01). Treatment with aminoguanidine reduced AGE plasma levels when compared with untreated diabetic mice (P < 0.001). After 28 days of ischemia, ischemic/nonischemic leg angiographic score, capillary density, and laser Doppler skin-perfusion ratios were 1.4-, 1.5-, and 1.4-fold decreased in diabetic mice in reference to controls (P < 0.01). Treatment with aminoguanidine completely normalized ischemia-induced angiogenesis in diabetic mice. We next analyzed the role of proteolysis in AGE formation-induced hampered neovascularization process. After 3 days of ischemia, MMP-2 activity and MMP-3 and MMP-13 protein levels were increased in untreated and aminoguanidine-treated diabetic mice when compared with controls (P < 0.05). Despite this activation of the MMP pathway, collagenolysis was decreased in untreated diabetic mice. Conversely, treatment of diabetic mice with aminoguanidine restored collagenolysis toward levels found in control mice. In conclusion, blockade of AGE formation by aminoguanidine normalizes impaired ischemia-induced angiogenesis in diabetic mice. This effect is probably mediated by restoration of matrix degradation processes that are disturbed as a result of AGE accumulation.     

Increased levels of advanced glycosylation end products in the kidney and liver from spontaneously diabetic Chinese hamsters determined by immunochemical assay

Increased levels of advanced glycosylation end products (AGEs) have been reported in tissues in association with diabetes mellitus. Thus, we measured tissue AGE levels and detected an accumulation of AGEs in the kidney and liver from spontaneously diabetic Chinese hamsters (CHAD) to determine the relationship between AGEs and diabetes mellitus. Diabetic CHAD aged 12 to 13 months were studied together with age-matched nondiabetic CHAD. We used an AGE-specific noncompetitive enzyme-linked immunosorbent assay (ELISA) with polyclonal anti-AGE-bovine serum albumin (BSA) antibody to measure tissue AGE levels. The samples extracted from the kidney and liver obtained from diabetic and nondiabetic CHAD reacted with anti-AGE-BSA antibody. When the absorbance of standard AGE-BSA (0.1 microg/mL) was expressed as 1 U, AGE levels in the kidney and liver from diabetic CHAD were significantly increased as compared with nondiabetic CHAD (kidney, 0.26 +/- 0.05 v 0.10 +/- 0.03 U/microg protein, P< .01; liver, 0.20 +/- 0.03 v 0.09 +/- 0.02 U/microg protein, P< .01). Positive AGE staining was observed in the renal cortex, especially in the tubules of diabetic CHAD, but little AGE staining was observed in the glomerulus by the immunohistochemical study. AGE staining was diffuse in the hepatocytes. These AGE levels were significantly correlated with fasting plasma glucose and glycated hemoglobin (P < .01, respectively). In conclusion, we have confirmed that AGE structures were expressed in the kidney and liver from CHAD, and these AGE levels were increased in diabetic CHAD. AGE staining was observed in the renal tubules and hepatocytes. Tissue AGE levels were positively correlated with glycemic control in CHAD.     

糖尿病大鼠血红蛋白糖基化终产物与肾脏改变的关系及意义

目的　探讨糖尿病大鼠血红蛋白糖基化终末产物 (Hb AGE)与肾脏改变的关系。方法采用竞争性酶联免疫吸附分析法 (ELISA)检测 44只 12周和 2 8周病程的链脲佐菌素 (STZ) 糖尿病大鼠和 14只正常对照大鼠的Hb AGE含量 ,并测定尿蛋白 /肌酐 (Pr/Cr)比值及病程 2 8周时的肾小球基底膜厚度 (GBMT)。结果　随着病程的延长 ,Hb AGE水平显著增高 (P <0 .0 1) ,与血糖和HbA1c呈显著性正相关 ,但与HbA1c的关系更密切。Hb AGE与肾小球组织AGE(GTE AGE)含量呈显著性正相关 (r=0 .6 86 2 ,P <0 .0 1) ,二者与尿Pr/Cr比值和GBMT具显著相关性 ;胰岛素和氨基胍可降低Hb AGE水平 ,减少尿蛋白 ,阻止基底膜增厚。结论　Hb AGE可作为AGE循环标志物 ,反映慢性高血糖和肾小球AGE含量 ,有助于了解糖尿病时的肾脏改变 ,其水平长期增高可能是糖尿病肾病的一个危险因素。     

The meaning of serum levels of advanced glycosylation end products in diabetic nephropathy

It has been reported that advanced glycosylation end products (AGEs) play an important role in the development of diabetic complications. To evaluate the relationship between serum AGEs and diabetic nephropathy, we measured serum AGE levels in diabetic patients with normoalbuminuria (N), microalbuminuria (M), overt proteinuria (O), and hemodialysis (HD), non diabetic patients with nephropathy, and age-matched control subjects using the enzyme-linked immunosorbent assay (ELISA). Urine AGE levels were also measured in these subjects except group HD. Serum AGE levels in diabetic patients were not significantly higher than those in the normal subjects. When we compared serum AGE levels among various stages of diabetic nephropathy, groups O and HD had significantly higher serum AGE levels than the other groups. Serum AGE levels in group HD were almost 6-fold higher than those in groups N and M. In contrast, there were no significant differences in urinary AGE levels among any diabetic groups. As for the variables that determine serum AGE levels in diabetic patients, there was no significant correlation between serum AGEs and fasting blood glucose, hemoglobin A1c (HbA1c), or duration of diabetes. In contrast, serum AGEs showed a strong correlation with serum creatinine and an inverse correlation with creatinine clearance. To evaluate the relationship between serum AGEs and oxidative stress in diabetic nephropathy, urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and serum malondialdehyde (MDA), which are biological markers of total oxidative stress in vivo, were also examined. Both urinary 8-OHdG and serum MDA levels were significantly higher in diabetic patients with proteinuria versus those without proteinuria. However, there was no significant correlation between serum AGEs and urinary 8-OHdG or serum MDA levels in diabetic patients. These results suggest that the accumulation of serum AGEs in diabetic nephropathy may be mainly due to decreased removal in the kidney rather than increased production by high glucose levels or oxidative stress.     

Prevention of glomerular basement membrane thickening by aminoguanidine in experimental diabetes mellitus

The etiology of diabetic glomerulopathy appears to be related, at least in part, to the degree of hyperglycemia, the resultant nonenzymatic glycosylation of proteins, and the eventual formation of advanced glycosylation end products in long-lived structural proteins. To investigate the relationship between the glomerular basement membrane (GBM) changes of diabetic nephropathy and the formation of advanced glycosylation end products, we studied control rats, diabetic rats, and control and diabetic rats who received aminoguanidine, a compound that pharmacologically inhibits formation of advanced glycosylation end products. After 9 months, rat weight was smaller and kidney weight larger in both diabetic groups compared with both control groups. GBM width was increased in the diabetic group compared with the control group. Aminoguanidine administration to diabetic rats ameliorated this increase in GBM. Thus, aminoguanidine administration from the onset of experimental diabetes prevented the widening of the GBM that is typical of diabetes.     

Role of advanced glycation end products (AGEs) and receptor for AGEs (RAGE) in vascular damage in diabetes

A non-enzymatic reaction between ketones or aldehydes and the amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules and to the development and progression of various age-related disorders such as vascular complications of diabetes, Alzheimer's disease, cancer growth and metastasis, insulin resistance and degenerative bone disease. Under hyperglycemic and/or oxidative stress conditions, this process begins with the conversion of reversible Schiff base adducts, and then to more stable, covalently-bound Amadori rearrangement products. Over a course of days to weeks, these early glycation products undergo further reactions and rearrangements to become irreversibly crossed-linked, fluorescent protein derivatives termed advanced glycation end products (AGEs). There is a growing body of evidence that AGE and their receptor RAGE (receptor for AGEs) interaction elicits oxidative stress, inflammatory reactions and thrombosis, thereby being involved in vascular aging and damage. These observations suggest that the AGE-RAGE system is a novel therapeutic target for preventing diabetic vascular complications. In this paper, we review the pathophysiological role of the AGE-RAGE-oxidative stress system and its therapeutic intervention in vascular damage in diabetes. We also discuss here the potential utility of the restriction of food-derived AGEs in diabetic vascular complications.