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.     

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.     

Exogenous advanced glycosylation end products induce complex vascular dysfunction in normal animals: a model for diabetic and aging complications.

Advanced glycosylation end products (AGEs) have been implicated in many of the complications of diabetes and normal aging. Markedly elevated vascular tissue and circulating AGEs were linked recently to the accelerated vasculopathy of end-stage diabetic renal disease. To determine the pathogenic role of AGEs in vivo, AGE-modified albumin was administered to healthy nondiabetic rats and rabbits alone or in combination with the AGE-crosslink inhibitor aminoguanidine. Within 2-4 weeks of AGE treatment, the AGE content of aortic tissue samples rose to six times the amount found in controls (P < 0.001). Cotreatment with aminoguanidine limited tissue AGE accumulation to levels two times that of control. AGE administration was associated with a significant increase in vascular permeability, as assessed by 125I label tracer methods. This alteration was absent in animals that received aminoguanidine in addition to AGE. Significant mononuclear cell migratory activity was observed in subendothelial and periarteriolar spaces in various tissues from AGE-treated rats compared to normal cellularity noted in tissues from animals treated with aminoguanidine. Blood pressure studies of AGE-treated rats and rabbits revealed markedly defective vasodilatory responses to acetylcholine and nitroglycerin compared to controls (P < 0.001), consistent with marked NO. inactivation; aminoguanidine treatment significantly prevented this defect. These in vivo data demonstrate directly that AGEs, independent of metabolic or genetic factors, can induce complex vascular alterations resembling those seen in diabetes or aging. AGE administration represents an animal model system for the study of diabetic and aging complications as well as for assessing the efficacy of newly emerging therapies aimed at inhibiting advanced glycosylation.     

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     

Advanced glycation end products up-regulate gene expression found in diabetic glomerular disease.

Several lines of evidence suggest that the excessive accumulation of extracellular matrix in the glomeruli of diabetic kidneys may be due to reactive intermediates forming between glucose and matrix proteins called advanced glycation end products (AGEs). Normal mice received AGE-modified mouse serum albumin i.p. for 4 weeks, and glomerular extracellular matrix, growth factor mRNA levels, and morphology were examined. We found that AGE induced an increase in glomerular extracellular matrix alpha 1(IV) collagen, laminin B1, and transforming growth factor beta 1 mRNA levels, as measured by competitive PCR, as well as glomerular hypertrophy. The AGE response was specific because the coadministration of an AGE inhibitor, aminoguanidine, reduced all these changes. We conclude that AGEs affected expression of genes implicated in diabetic kidney disease and may play a major role in nephropathy.     

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。     

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.     

Positive association between serum levels of advanced glycation end products and the soluble form of receptor for advanced glycation end products in nondiabetic subjects

The advanced glycation end products (AGEs)-receptor for AGE (RAGE) axis is implicated in diabetic vascular complications. Administration of soluble form of RAGE (sRAGE) to mice has been shown to block the AGE-elicited tissue damage by acting as a decoy. These observations suggest that endogenous sRAGE may capture and eliminate circulating AGEs and decrease its serum levels. However, because AGEs up-regulate tissue RAGE expression and endogenous sRAGE could be generated from the cleavage of cell surface RAGE, sRAGE may be positively, rather than inversely, associated with circulating AGEs by reflecting tissue RAGE expression. In this study, we investigated the association of sRAGE with serum levels of AGEs in humans. Data for fasting serum sRAGE and AGE levels of 184 nondiabetic subjects were obtained from a general population in Japan. We also measured body mass index (BMI), waist circumference, blood pressure, and blood biochemistries in this population. Uni- and multivariate analyses were applied for the determinants of serum sRAGE levels. The average sRAGE levels were 0.40 +/- 0.17 ng/mL in males and 0.43 +/- 0.14 ng/mL in females, respectively. In the univariate analysis, BMI (P < .05, inversely), waist circumference (P < .05, inversely), AGEs (P < .05), and alcohol intake (P < .05, inversely) were significantly associated with sRAGE levels. After performing multivariate analyses, BMI (P < .05, inversely) and AGEs (P < .05) still remained significant independently. The present study is the first demonstration that serum sRAGE levels were positively associated with circulating AGEs in the nondiabetic general population. Endogenous sRAGE levels are elevated in parallel with serum AGE levels.     

糖尿病小鼠缺血诱导的骨髓内皮祖细胞动员障碍

目的 观察糖尿病动物缺血诱导的骨髓内皮祖细胞（EPC）动员是否存在障碍,以及这种障碍是否和缺血诱导的血管内皮生长因子（VEGF）释放降低有关。方法 链脲霉素40mg／kg诱导C5781／6雄鼠糖尿病,非糖尿病组给予等量缓冲液。饲养2个月后,进行左侧股动脉高位结扎离断术造成后肢缺血模型,通过红四氮唑染色法与后肢血管造影确定造模成功。于术前及术后不同时间点采血（1天,3天,n：8;5天,7天及14天,n=5）,三色流式细胞术检测两组动物外周血单个核细胞中c-Ki^＋／Sea-1^＋／flk-1^＋早期EPC比例。ELISA法测定相应时间点血浆VEGF水平。结果 基础状态下,糖尿病组循环EPC数量较非糖尿病组明显减少[（0．60±0．03）％比（0．95±0．09）％,P〈0．001],血浆VEGF水平低于试剂盒检测灵敏度。两组动物缺血诱导的骨髓早期EPC释放曲线相似,即术后1天显著增加,术后3天达峰,动员持续至2周以上。但是在EPC早期快速动员阶段（术后前3天）,糖尿病组外周血早期EPC数量较非糖尿病组明显减少[1天,（1．16±0．29）％比（1．80±0．32）％,P〈0．05;3天,（1．38±0．34）％比（2．37±0．52）％,P〈0．05]。同时组织缺血也伴随着血浆VEGF浓度的显著增高：非糖尿病组血浆VEGF水平在术后一天快速增加并达到峰值,此后渐降至相对较低水平持续两周以上;而糖尿病组术后1天血浆VEGF快速释放明显降低[（73．1±18．6）pg／ml比（128．5±44．2）Pg／ml,P〈0．05]。结论 糖尿病动物基础状态下外周血早期EPC数量减少,组织缺血诱导的骨髓EPC动员障碍,这种障碍可能与缺血诱导的VEGF释放减少有关。     

Regulation of matrix metalloproteinase activity in ischemic tissue by interleukin-10: role in ischemia-induced angiogenesis

We have previously shown that deficiency in the anti-inflammatory cytokine interleukin-10 (IL-10) is responsible for enhanced angiogenesis after hindlimb ischemia. This study examined the putative involvement of matrix metalloproteinase (MMP) activation in this process. Ischemia was produced by artery femoral occlusion in both C57BL6 IL-10(+/+) and IL-10(-/-) mice. Angiographic vessel density and laser Doppler perfusion data at day 28 showed significant improvement in ischemic/nonischemic leg ratio by, respectively, 1.8-fold and 1.4-fold in IL-10(-/-) mice compared with IL-10(+/+) mice. This was associated with an increase in vascular endothelial growth factor (VEGF) protein content in the ischemic hindlimb. Three days after ischemia, gelatin zymography showed a significant increase in both pro- and active forms of MMP-2 and MMP-9 in ischemic hindlimbs of IL-10(-/-) mice compared with IL-10(+/+) mice (P<0.01). This increase in MMP activity in IL-10(-/-) mice was completely inhibited by treatment with BB-94 (5 mg/kg IP), a specific MMP inhibitor. Furthermore, increases in both vessel density and blood perfusion indexes at day 28 in IL-10(-/-) mice were abolished after treatment with BB-94 (0.78+/-0.06 versus 1.17+/-0.09 and 0.62+/-0.02 versus 0.88+/-0.04, for vessel density and blood perfusion ratio, respectively, in IL-10(-/-) mice treated with BB-94 versus untreated IL-10(-/-) mice, P<0.05). In contrast, BB-94 treatment did not affect the rise in VEGF protein content. These findings in IL-10(-/-) mice underscore the critical role of MMP activation, in a context of increased VEGF expression, in promoting ischemia-induced angiogenesis.     

Inflammatory mediators are induced by dietary glycotoxins,a major risk factor for diabetic angiopathy

Diet is a major environmental source of proinflammatory AGEs (heat-generated advanced glycation end products); its impact in humans remains unclear. We explored the effects of two equivalent diets, one regular (high AGE, H-AGE) and the other with 5-fold lower AGE (L-AGE) content on inflammatory mediators of 24 diabetic subjects: 11 in a 2-week crossover and 13 in a 6-week study. After 2 weeks on H-AGE, serum AGEs increased by 64.5% (P = 0.02) and on L-AGE decreased by 30% (P = 0.02). The mononuclear cell tumor necrosis factor-alphabeta-actin mRNA ratio was 1.4 +/- 0.5 on H-AGE and 0.9 +/- 0.5 on L-AGE (P = 0.05), whereas serum vascular adhesion molecule-1 was 1,108 +/- 429 and 698 +/- 347 ngml (P = 0.01) on L- and H-AGE, respectively. After 6 weeks, peripheral blood mononuclear cell tumor necrosis factor-alpha rose by 86.3% (P = 0.006) and declined by 20% (P, not significant) on H- or L-AGE diet, respectively; C-reactive protein increased by 35% on H-AGE and decreased by 20% on L-AGE (P = 0.014), and vascular adhesion molecule-1 declined by 20% on L-AGE (P < 0.01) and increased by 4% on H-AGE. Serum AGEs were increased by 28.2% on H-AGE (P = 0.06) and reduced by 40% on L-AGE (P = 0.02), whereas AGE low density lipoprotein was increased by 32% on H-AGE and reduced by 33% on L-AGE diet (P < 0.05). Thus in diabetes, environmental (dietary) AGEs promote inflammatory mediators, leading to tissue injury. Restriction of dietary AGEs suppresses these effects.     

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.     

Activation of receptor for advanced glycation end products in osteoarthritis leads to increased stimulation of chondrocytes and synoviocytes

OBJECTIVE: The major risk factor for osteoarthritis (OA) is aging, but the mechanisms underlying this risk are only partly understood. Age-related accumulation of advanced glycation end products (AGEs) could be one of these mechanisms. We undertook this study to investigate the role of the receptor for AGEs (RAGE) in mediating the cellular effects of AGEs on chondrocytes and fibroblast-like synoviocytes (FLS). METHODS: AGE levels in human cartilage were determined by fluorescence, browning, and pentosidine levels. Chondrocyte activation by AGEs was assessed as the release of proteoglycans and the synthesis of matrix metalloproteinase 1 (MMP-1) and type II collagen messenger RNA (mRNA). The activation of FLS by AGEs was measured by MMP-1 production and invasion through matrix proteins. RESULTS: Patients with focal degeneration of cartilage showed increased AGE levels in their healthy cartilage compared with the levels in healthy cartilage from donors without cartilage degeneration (P < 0.01 for both fluorescence and browning; P not significant for pentosidine content). Stimulation of bovine chondrocytes with glycated albumin increased the release of proteoglycans by 110% (P < 0.001) and the production of MMP-1 mRNA by 200% (P = 0.028). In addition, OA FLS produced 240% more MMP-1 when stimulated with glycated albumin (P < 0.001). Glycated matrix or albumin increased the catabolic activity of OA FLS, which was assessed as invasive behavior, by 150% and 140% (P = 0.001 and P = 0.010), respectively. Effects of stimulation with AGEs were blocked by a neutralizing antibody against RAGE, but not by an isotype control. CONCLUSION: This study shows that AGEs trigger RAGE on chondrocytes and FLS, leading to increased catabolic activity and therefore to cartilage degradation. AGEs, via RAGE, could therefore contribute to the development and/or progression of OA.     

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.     

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     

The relative roles of advanced glycation,oxidation and aldose reductase inhibition in the development of experimental diabetic nephropathy in the Sprague-Dawley rat

Summary Advanced glycation is an important pathogenic mechanism in the development of diabetic complications. However, other biochemical processes, such as the polyol pathway or lipid and protein oxidation which can interact with advanced glycation can also yield tissue fluorescence and may also be implicated in the genesis of diabetic microangiopathy. Aminoguanidine is an inhibitor of advanced glycation, but it is not known if all of its effects are mediated by this mechanism. The present study explores the relative contributions of aldose reductase, oxidative stress and advanced glycation on the development of aortic and renal fluorescence and urinary albumin excretion in streptozotocin diabetic rats. The study groups included non-diabetic (control), streptozotocin diabetic rats and diabetic rats receiving aminoguanidine, the anti-oxidants butylated hydroxytoluene and probucol and the aldose reductase inhibitor, ponalrestat. Serial measurements of glycaemic control and urinary albumin excretion were performed every 8 weeks. At 32 weeks, animals were killed, tissues removed and collagen extracted for measurement of fluorescence. Diabetic rats had increased fluorescence in aorta, glomeruli and renal tubules. Aminoguanidine prevented an increase in fluorescence at all three sites suggesting that diabetes-related tissue fluorescence is predominantly due to advanced glycation. Ponalrestat retarded fluorescence in aorta only and butylated hydroxytoluene attenuated fluorescence at the renal sites but not in the aorta. Diabetic rats had increased renal cortical sorbitol levels. Ponalrestat normalized renal cortical sorbitol levels but aminoguanidine did not affect this parameter. The only agent to decrease plasma thiobarbituric acid reactive substances was butylated hydroxytoluene. Diabetic rats developed albuminuria over the 32-week period. This increase in urinary albumin excretion was only attenuated significantly by aminoguanidine therapy, but not by probucol or ponalrestat. The effects of butylated hydroxytoluene on albuminuria were intermediate between aminoguanidine-treated and untreated diabetic rats. The failure of either antioxidants or aldose reductase inhibition to reproduce the renal effects of aminoguanidine suggest that aminoguanidine may act predominantly via inhibition of advanced glycation and not via the alternative biochemical processes evaluated in this study.Abbreviations AGE Advanced glycated end products - AG aminoguanidine - TBARS Thiobarbituric acid reactive substances - BHT butylated hydroxytoluene     

Prevention of early renal disease, dyslipidaemia and lipid peroxidation in STZ-diabetic rats by LR-9 and LR-74, novel AGE inhibitors

BACKGROUND: Increased formation of advanced glycation/lipoxidation endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several compounds have been developed as inhibitors of AGE/ALE formation. We examined the effects of two new AGE/ALE inhibitors, LR-9 and LR-74, on the development of early renal disease and lipid metabolism in streptozotocin (STZ)-induced diabetic rats. METHODS: Diabetic Sprague-Dawley rats were treated with either of the LR compounds for 32 weeks. Progression of renal disease was evaluated by measurements of urinary albumin and plasma creatinine concentrations. AGE/ALE and nitrotyrosine levels in kidneys were determined by immunohistochemistry. AGE-induced chemical modification of the tail tendon collagen and levels of Nepsilon-(carboxymethyl) and (carboxyethyl)- lysines (CML and CEL) in skin collagen were measured. Plasma lipids and their lipid hydroperoxide concentrations were also determined. In vitro, both compounds were tested for inhibiting lipid peroxidation reactions. RESULTS: Treatment of either LR compounds significantly inhibited the increase in albuminuria, creatinaemia, hyperlipidaemia and lipid peroxidation in diabetic rats without any effect on hyperglycaemia. Both compounds also reduced CML-AGE and nitrotyrosine accumulation in kidney glomeruli and tubules, AGE-linked fluorescence and cross-linking of tail collagen, and levels of CML and CEL in skin collagen. In vitro, LR compounds inhibited the oxidation of human low-density lipoprotein (LDL). CONCLUSION: Both compounds can inhibit the progression of renal disease and also prevent dyslipidaemia in type-1 diabetic animals. These compounds may have an additional beneficial effect as an antioxidant against lipid peroxidation, and thus may provide alternative therapeutic options for the treatment of various diabetic macrovascular complications.     

晚期糖基化终末产物对糖尿病大鼠主动脉结构和功能的影响

目的探讨晚期糖基化终末产物(AGEs)对主动脉血管结构和功能影响及氨基胍的保护作用。方法将80只雄性SD大鼠随机分为4组:空白对照组(A组),糖尿病组(B组),糖尿病氨基胍干预组(C组)和空白氨基胍干预组(D组),每组20只。药物应用12周观察主动脉功能和结构变化。结果与A组和D组比较,B组、C组主动脉环对去甲肾上腺素引起的收缩反应明显增强,对乙酰胆碱引起的舒张反应则均明显减弱,C组反应强度较B组明显减轻(P0.05,P0.01)。主动脉壁均有AGEs沉积,B组、C组较明显,C组较B组明显减轻(P0.01);超微结构观察显示,A组、D组主动脉内膜大致正常,B组、C组内膜破坏明显,与动脉环结果呈一致性趋势。结论糖尿病大鼠主动脉AGEs含量增多,损伤了主动脉的结构和功能,氨基胍能够减少AGEs的沉积,并对主动脉结构和功能有保护作用。     

Potential benefit of inhibitors of advanced glycation end products in the progression of type II diabetes: A study with aminoguanidine in C57/BLKsJ diabetic mice

Prolonged hyperglycemia in type II diabetic patients is linked both with diabetic complications and with further impairment of glucose homeostasis, possibly due to glucose toxicity of the β cell. While the connection between the accumulation of extracellular advanced glycation end products (AGEs) and the development of complications is well established, it has only recently been suggested that intracellular glycation may be equally adverse and could be involved in the pathogenesis of glucose toxicity in vitro. Aminoguanidine is a recognized inhibitor of the formation of both extracellular and intracellular AGEs. In this study, we show that the development of diabetes, measured by increased water intake and concomitant midday blood glucose levels in type II genetically diabetic mice, is reduced by treatment with aminoguanidine at a dosage of 500 mg/kg/d for 12 weeks in the diet. In addition, at the end of the study, aminoguanidine reduced the decline in serum and pancreatic insulin levels and the degree of pancreatic islet morphological degeneration, all of which are associated with pancreatic insufficiency following prolonged hyperglycemia in this animal model. These results suggest that AGEs may be involved in the aggravation of type II diabetes in vivo and aminoguanidine may be beneficial in its treatment.     

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.