Progression of nephropathy in spontaneous diabetic rats is prevented by OPB-9195, a novel inhibitor of advanced glycation

Glucosamine prevents in vitro collagen degradation in chondrocytes by inhibiting advanced lipoxidation reactions and protein oxidation

Osteoarthritis (OA) affects a large segment of the aging population and is a major cause of pain and disability. At present, there is no specific treatment available to prevent or retard the cartilage destruction that occurs in OA. Recently, glucosamine sulfate has received attention as a putative agent that may retard cartilage degradation in OA. The precise mechanism of action of glucosamine is not known. We investigated the effect of glucosamine in an in vitro model of cartilage collagen degradation in which collagen degradation induced by activated chondrocytes is mediated by lipid peroxidation reaction. Lipid peroxidation in chondrocytes was measured by conjugated diene formation. Protein oxidation and aldehydic adduct formation were studied by immunoblot assays. Antioxidant effect of glucosamine was also tested on malondialdehyde (thiobarbituric acid-reactive substances [TBARS]) formation on purified lipoprotein oxidation for comparison. Glucosamine sulfate and glucosamine hydrochloride in millimolar (0.1 to 50) concentrations specifically and significantly inhibited collagen degradation induced by calcium ionophore-activated chondrocytes. Glucosamine hydrochloride did not inhibit lipid peroxidation reaction in either activated chondrocytes or in copper-induced oxidation of purified lipoproteins as measured by conjugated diene formation. Glucosamine hydrochloride, in a dose-dependent manner, inhibited malondialdehyde (TBARS) formation by oxidized lipoproteins. Moreover, we show that glucosamine hydrochloride prevents lipoprotein protein oxidation and inhibits malondialdehyde adduct formation in chondrocyte cell matrix, suggesting that it inhibits advanced lipoxidation reactions. Together, the data suggest that the mechanism of decreasing collagen degradation in this in vitro model system by glucosamine may be mediated by the inhibition of advanced lipoxidation reaction, preventing the oxidation and loss of collagen matrix from labeled chondrocyte matrix. Further studies are needed to relate these in vitro findings to the retardation of cartilage degradation reported in OA trials investigating glucosamine.

Role of the AGE crosslink breaker, alagebrium, as a renoprotective agent in diabetes

The biochemical process of advanced glycation appears to play a central role in the development and progression of diabetic vascular complications. A number of strategies to influence this pathway have been designed, one of which involves the putative advanced glycation end-product (AGE) crosslink breaker, alagebrium which has been shown in in vitro studies to cleave preformed AGE crosslinks. This agent has been studied in various models of diabetic complications and has been shown to attenuate diabetic renal disease, cardiac dysfunction, and atherosclerosis. In addition to the ability of alagebrium to reduce tissue levels of AGEs, this drug appears to inhibit activation of certain protein kinase C isoforms. Planned clinical studies in diabetic subjects at risk of complications should assist in determining the role of alagebrium in the prevention, retardation, and reversal of diabetic micro- and macrovascular disease.

Intervention strategies to inhibit protein carbonylation by lipoxidation-derived reactive carbonyls

Protein carbonylation induced by reactive carbonyl species (RCS) generated by peroxidation of polyunsaturated fatty acids plays a significant role in the etiology and/or progression of several human diseases, such as cardiovascular (e.g., atherosclerosis, long-term complications of diabetes) and neurodegenerative diseases (e.g., Alzheimer's disease, Parkinson's disease, and cerebral ischemia). Most of the biological effects of intermediate RCS, mainly alpha,beta-unsaturated aldehydes, di-aldehydes, and keto-aldehydes, are due to their capacity to react with the nucleophilic sites of proteins, forming advanced lipoxidation end-products (ALEs). Because of the emerging deleterious role of RCS/protein adducts in several human diseases, different potential therapeutic strategies have been developed in the last few years. This review sheds focus on fundamental studies on lipid-derived RCS generation, their biological effects, and their reactivity with proteins, with particular emphasis to 4-hydroxy-trans-2-nonenal (HNE)-, acrolein (ACR)-, malondialdehyde (MDA)-, and glyoxal (GO)-modified proteins. It also discusses the recently developed pharmacological approaches for the management of chronic diseases in which oxidative stress and RCS formation are massively involved. Inhibition of ALE formation, based on carbonyl-sequestering agents, seems to be the most promising pharmacological tool and is reviewed in detail.

Advanced Glycation End Products and Nephrotoxicity of High-Protein Diets

The popularity of high-protein diets has surged recently as obesity has become more and more common in the United States and other developed nations. In view of the high prevalence of type 2 diabetes and chronic kidney disease among obese people, it is important to understand potential effects of high-protein diets on the kidney. The hypothesis that high-protein diets are nephrotoxic because of their excessive dietary advanced glycation end product (AGE) content and an increased amino acid load that enhances AGE formation in situ was explored. This review discusses the following evidence: (1) High-protein diets are deleterious to the kidney; (2) AGE are metabolic mediators of kidney damage; (3) dietary protein-derived AGE contribute to proinflammatory and pro-oxidative processes in diabetes and kidney disease; and (4) dietary protein-derived AGE produce functional and structural abnormalities that are involved in kidney damage. Future research should consider dietary AGE as a potential therapeutic target for kidney disease in obesity, diabetes, and perhaps other causes of chronic kidney disease.

Prevention and reversal of diabetic nephropathy in db/db mice treated with alagebrium (ALT-711)

BACKGROUND

Alagebrium (ALT-711) has been shown to improve renal dysfunction in animal models of diabetes.

METHODS

To test its effects in diabetic nephropathy (DN), ALT-711 was administered (1 mg/kg daily i.p.) to 9-week-old female db/db mice (n = 15, group A1) for 3 weeks and to 3-month-old (n = 15, group A2), 7-month-old (n = 7, group A3), and 12-month-old (n = 5, group A4) female db/db mice for 12 weeks, while a similar number of diabetic and nondiabetic mice were used as controls. The epsilonN-carboxymethyllysine (CML) levels in serum, urine, skin, and kidney tissue were measured by enzyme-linked immunosorbent assay. The renal morphometric parameters were assessed by electron and light microscopy.

RESULTS

By the 3rd week of treatment, the serum CML level decreased by 41%, and the urinary CML concentration increased by 138% from baseline, while the urinary albumin/creatinine ratio was lower (p < 0.05) in diabetic and nondiabetic group A1 mice. After 3 months of treatment, serum, skin, and kidney CML levels and urinary albumin/creatinine ratio were lower (p < 0.05) and the urinary CML levels higher (p < 0.05) in treated group A2, A3, and A4 animals compared with groups which received phosphate-buffered saline, with a similar pattern observed in nondiabetic mice. The renal morphological parameters characteristic of DN decreased in treated compared with untreated mice.

CONCLUSION

Alagebrium may prevent, delay, and/or reverse established DN in db/db mice by reducing the systemic advanced glycation end product pools and facilitating the urinary excretion of advanced glycation end products.

Contribution of p16INK4aand p21CIP1pathways to induction of premature senescence of human endothelial cells: permissive role of p53

We have previously found that nonenzymatically glycated collagen I (GC), mimicking diabetic microenvironment, can induce senescent phenotype in early passage human umbilical vein endothelial cells (HUVECs). In the present study, we explored the functional involvement of cell cycle checkpoint pathways in initiating GC-induced premature endothelial cell senescence. When compared with native collagen, early passage HUVECs showed increased p53, p21CIP1(p21), and p16INK4a(p16) mRNA expression after exposure to GC. Twenty-four hours after transfection of p16, p21, and p53-enhanced green fluorescent protein (EGFP) recombinant plasmids, HUVECs entered G1-phase cell cycle arrest. By days 3 and 5, HUVECs transfected with p16-EGFP showed an increased proportion of senescent cells, and this increase was more prominent in the GFP-positive cell population, which exhibited 68% of senescent cells. Transfection of p21 also induced senescence but only by day 5. Cotransfection of p16 and p21 showed no additive effect. Transfection of p21 or p53 induced apoptosis in HUVECs. Next, we suppressed endogenous p53, p21, p16, or retinoblastoma (Rb) gene expression through small interference RNA strategy and investigated their influence in p16- and p21-initiated endothelial cell senescence. Analysis indicated that suppression of p53 expression can abolish senescence induced by p16 overexpression. Paradoxically, this effect was not observed when p21 was suppressed. On the other hand, suppression of Rb eliminated senescence initiated by either p16 or p21 overexpression. In summary, the p53/p21 pathway is mainly responsible for GC-induced apoptosis, but the coordinated activation of the p53/p21 and p16 pathway is responsible for GC-induced endothelial cell senescence through a Rb-dependent mechanism.

Antioxidants and an inhibitor of advanced glycation ameliorate death of retinal microvascular cells in diabetic retinopathy

BACKGROUND

Pericyte ghosts and acellular capillaries are well known as early histological changes resulting from diabetic retinopathy. These histological changes mean that the cell death of retinal microvessels has accelerated. It was reported that apoptosis of retinal microvascular cells (RMCs) was increased in diabetic patients. Therefore, we investigated apoptosis of RMCs in Goto-Kakizaki (GK) rats, a type 2 diabetic model, and involvement with antioxidants (a combination of vitamins C and E) or a novel inhibitor of advanced glycation, OPB-9195.

METHODS

GK rats were treated with the antioxidants combination or OPB-9195 for 36 weeks. We obtained isolated preparations of the vascular network from their retinas by trypsin digestion. Apoptosis of retinal vascular cells was detected with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay.

RESULTS

We found that apoptosis of RMCs was increased in the diabetic GK rats. Furthermore, a combination of vitamins C and E and an advanced glycation end-products inhibitor mostly inhibited this increased apoptosis.

CONCLUSIONS

We concluded that apoptosis of RMCs was a good marker that indicates the progression of diabetic retinopathy in GK rats. Both oxidative stress and the accumulation of advanced glycation end-products appears to promote the apoptosis of retinal microvascular cells, and antioxidants or advanced glycation end-products inhibitors might ameliorate diabetic retinopathy.

From molecular footprints of disease to new therapeutic interventions in diabetic nephropathy

Proteins are particularly attractive targets for product analysis, which is used to understand pathology. Protein modifications, such as advanced glycation end products (AGEs), serve as footprints of biochemical processes and also help in the search for novel agents that efficiently inhibit protein damage. Interestingly, several medical agents that are used clinically interfere with oxidative protein damage through different mechanisms characteristic of their chemical structures. We recently found that angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) lower the in vitro formation of the AGEs pentosidine and carboxymethyllysine. Their inhibition for AGE formation is more striking than aminoguanidine. Unlike aminoguanidine, ARBs and ACEIs do not trap reactive carbonyl precursors of AGEs. Rather, they inhibit AGE formation, possibly as a result of their potent ability to scavenge hydroxyl radicals and to chelate the transition metals necessary for the Fenton reaction. We tested their AGE-lowering ability in vivo in a unique type-2 diabetic model with nephropathic SHR/NDmcr-cp rats, which exhibits the metabolic syndrome (obesity, hyperglycemia, hyperlipidemia, hyperinsulinemia) in addition to hypertension. Obesity and associated metabolic derangements, in addition to hypertension, markedly accelerate renal injury. Expectedly, correction of hyperglycemia and hyperinsulinemia partially but significantly improves renal injury. A low-calorie diet greatly improves renal injury despite persistent hypertension. Among antihypertensive agents, ARBs, unlike nifedipine and atenolol, are renoprotective despite persistent metabolic syndrome, but their action is independent of blood pressure lowering and is observed in a dose-dependent manner despite the complete blockade of angiotensin II receptor. Interestingly, the improvement of renal injury by ARBs as well as a low-calorie diet is associated with a significant reduction in local oxidative stress and AGE formation in the kidney. During the characterization of the AGE-lowering profile of our chemical compound libraries ( approximately 2000), we identified several inhibitors of oxidative stress and advanced glycation. They are indeed renoprotective, independently of correction of hypertension and metabolic syndrome, in experimental diabetic nephropathy and other nephritis models. Altogether, our data are in good agreement with the recent therapeutic concept for diabetic nephropathy that multiple risk factor interventions are critical in the treatment of diabetic renal injury, and further implicate a therapeutic potential of inhibition of oxidative stress and advanced glycation.

Pyridoxamine improves functional, structural, and biochemical alterations of peritoneal membranes in uremic peritoneal dialysis rats

BACKGROUND

We previously suggested that biochemical alterations of peritoneal membrane associated with long-term peritoneal dialysis might be, at least in part, accounted for by reactive carbonyl compounds overload originating both from uremic circulation and heat sterilization of glucose peritoneal dialysis fluid. In the present study, we utilized a uremic rat model on peritoneal dialysis and evaluated the protective effects of pyridoxamine, a recently developed inhibitor of advanced glycation end product (AGE), on structural, functional, and biochemical alterations of peritoneal membrane.

METHODS

Uremic rats were generated by subtotal nephrectomy, some of which were undergone peritoneal dialysis with dialysate and/or given intraperitoneal pyridoxamine. Functional [dialysate/plasma ratio (D/P)(urea, creatinine), D/D(0 glucose)], structural (density of blood vessels in peritoneal membrane tissues), and molecular biochemical [formation of pentosidine, an AGE, by high-performance liquid chromatography (HPLC) assay and expressions of vascular endothelial growth factor (VEGF), and fibroblast growth factor 2 (FGF-2), by semiquantitative polymerase chain reaction (PCR) and/or immunohistochemistry] alterations of peritoneal membrane were assessed.

RESULTS

Uremic peritoneal membrane was characterized by an increased functional area of exchange for small solutes between blood and dialysate, vascular proliferation, increased AGE genesis, and up-regulated expressions of angiogenic cytokines. The peritoneal membrane alterations associated with peritoneal dialysis are similar but more severe than those in uremia without peritoneal dialysis. Pyridoxamine given in uremic rats with peritoneal dialysis significantly improved functional and structural alterations. This improvement was accompanied by reduction of AGE accumulation and of angiogenic cytokines expressions.

CONCLUSION

Peritoneal carbonyl stress derived from uremia as well as peritoneal dialysis procedure might contribute to the vascular proliferation through induction of bioactive molecules and to an increased functional area, eventually leading to ultrafiltration failure. Pyridoxamine may be beneficial in protection of uremic peritoneal membrane on peritoneal dialysis.

Oxidative stress and stress signaling: menace of diabetic cardiomyopathy

Cardiovascular disease is the most common cause of death in the diabetic population and is currently one of the leading causes of death in the United States and other industrialized countries. The health care expenses associated with cardiovascular disease are staggering, reaching more than 350 billion dollars in 2003. The risk factors for cardiovascular disease include high fat/cholesterol levels, alcoholism, smoking, genetics, environmental factors and hypertension, which are commonly used to gauge an individual's risk of cardiovascular disease and to track their progress during therapy. Most recently, these factors have become important in the early prevention of cardiovascular diseases. Oxidative stress, the imbalance between reactive oxygen species production and breakdown by endogenous antioxidants, has been implicated in the onset and progression of cardiovascular diseases such as congestive heart failure and diabetes-associated heart dysfunction (diabetic cardiomyopathy). Antioxidant therapy has shown promise in preventing the development of diabetic heart complications. This review focuses on recent advances in oxidative stress theory and antioxidant therapy in diabetic cardiomyopathy, with an emphasis on the stress signaling pathways hypothesized to be involved. Many of these stress signaling pathways lead to activation of reactive oxygen species, major players in the development and progression of diabetic cardiomyopathy.

Vascular methylglyoxal metabolism and the development of hypertension

OBJECTIVES

The pathogenic process of diabetes mellitus is associated with increased methylglyoxal (MG). MG causes non-enzymic glycation of proteins to form irreversible advanced glycation endproducts (AGEs). However, the correlation between MG and essential hypertension is unknown. The aim of the present study was to investigate whether MG, MG-induced AGEs, and oxidative stress were increased in the aorta of spontaneously hypertensive rats (SHR) and whether an increased formation of MG and related AGEs was correlated with the development of high blood pressure in these rats.

METHODS

High-performance liquid chromatography (HPLC) was used to determine MG and reduced glutathione levels in plasma and aorta. MG-induced AGEs, N(epsilon)-carboxyethyl-lysine (CEL) and N(epsilon)-carboxymethyl-lysine (CML), in aorta were determined using immunohistochemistry. Hydrogen peroxide and superoxide levels in aorta and glutathione peroxidase and reductase activities were also determined.

RESULTS

Aortic and plasma MG levels were significantly elevated in SHR, but not in Wistar-Kyoto (WKY) rats, at 8, 13 and 20 weeks of age, in parallel with blood pressure increase. Immunohistochemistry revealed more intense staining for CML and CEL in aorta from SHR than those of WKY rats from 8 weeks onwards. Most of the staining was localized to endothelial cells. Superoxide and hydrogen peroxide levels were significantly elevated in aorta of SHR at 13 weeks, whereas reduced glutathione levels, glutathione peroxidase and glutathione reductase activities were significantly decreased compared to WKY rats.

CONCLUSIONS

Increased aortic MG, AGE formation and oxidative stress were associated with blood pressure increase in SHR, which may cause endothelial dysfunction and altered vascular reactivity.

Agents in development for the treatment of diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, and accounts for significant morbidity and mortality in patients with diabetes. Diabetic nephropathy seems to occur as a result of an interaction between metabolic and haemodynamic factors, which activate common pathways that lead to renal damage. In the past, the treatment of diabetic nephropathy has focused on the control of hyperglycaemia. Newer targets, some of which are linked to glucose-dependent pathways, appear to be a major focus of new treatments directed against the development and progression of renal damage as a result of diabetes. It is anticipated that additional therapeutic approaches that inhibit both metabolic and haemodynamic pathways will include strategies that target growth factors, cytokines and intracellular second messengers. Such an approach is expected to lead to improved therapies for the treatment of diabetic nephropathy.

Advanced glycation end products in kidney transplant patients: a putative role in the development of chronic renal transplant dysfunction

Chronic renal transplant dysfunction is one of the leading causes of graft failure in kidney transplantation. A complex interplay of both alloantigen-related and alloantigen-unrelated risk factors is believed to underlie its development. We propose that advanced glycation end products (AGEs) are involved in the development of chronic renal transplant dysfunction. AGE formation is associated with different alloantigen-unrelated risk factors for chronic renal transplant dysfunction, such as recipient age, diabetes, proteinuria, hypertension, and hyperlipidemia. In vitro studies have shown that AGEs induce the expression of various mediators associated with chronic renal transplant dysfunction. Furthermore, AGE-induced renal damage has been found in multiple experimental studies. This renal damage shows similarity to the damage found in chronic renal transplant dysfunction. Together, several lines of evidence support a role of AGEs in the development of chronic renal transplant dysfunction and suggest that preventive therapy with AGE inhibitors may be helpful in preserving renal function in transplant recipients.

TAGE (toxic AGEs) hypothesis in various chronic diseases

The advanced stage of the glycation process (one of the post-translational modifications of proteins) leads to the formation of advanced glycation end-products (AGEs) and plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative diseases. However, it is still not clear which AGEs subtypes play a pathogenetic role and which of several AGEs receptor mediate AGEs effects on cells. We have provided direct immunochemical evidence for the existence of six distinct AGEs structures (AGEs-1 to -6) within the AGEs-modified proteins and peptides that circulate in the serum of diabetic patients. Recently we demonstrated for the first time that glyceraldehyde-derived AGEs (AGEs-2) and glycolaldehyde-derived AGEs (AGE-3) have diverse biological activities on vascular wall cells, mesangial cells, Schwann cells, malignant melanoma cells and cortical neurons. We also demonstrated for the first time that acetaldehyde (AA)-derived AGEs (AA-AGE) have cytotoxic activity on cortical neurons and the AA-AGE epitope was detected in human brain of alcoholics. These results indicate that of the various types of AGEs structures that can form in vivo, the toxic AGEs (TAGE) structures (AGEs 2, 3, and AA-AGE), but not non-toxic AGEs (N-carboxymethyllysine, pentosidine, pyrraline etc.) are likely to play an important role in the pathophysiological processes associated with AGEs formation.

Increase in the Deposition of Aggregated Protein in the Glomeruli of Spontaneously Diabetic Mice

The aim of this study was to investigate the disposal of aggregated protein in the glomeruli of spontaneously diabetic mice. Diabetic mice, KK-A(y) and db/db, and age-matched ICR mice were injected intravenously with aggregated bovine serum albumin (a-BSA) at 0.6 mg/g, and the glomeruli and the blood were obtained. Diabetic mice had larger amounts of a-BSA in their glomeruli than the ICR mice, threefold in KK-A(y) and twofold in db/db, at 3 h after the a-BSA injection. Additionally, the disappearance of a-BSA was retarded in the diabetic glomeruli. KK-A(y) displayed a-BSA in the glomeruli 24 h after the a-BSA injection and db/db did after 12 h, while the ICR did by 8 h. In spite of increases of insulin to similar degrees in both strains of diabetic mice after the a-BSA injection, blood glucose levels markedly decreased in KK-A(y) compared with db/db. There were no histopathological alterations in the glomeruli of the diabetic mice. Depositions of a-BSA were confirmed to be higher in the diabetic glomeruli by the immunofluorescence technique, and KK-A(y) displayed higher depositions of a-BSA than did db/db. The present study suggests that hyperglycemia is involved in the increased deposition of aggregated protein in the glomeruli and that the degradation of aggregated protein is retarded in diabetic glomeruli.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Pyridoxal Phosphate and Hepatocyte Growth Factor Prevent Dialysate-Induced Peritoneal Damage

Glucose-based peritoneal dialysate (PD) is responsible for increased accumulation of advanced glycation end products (AGE) in the peritoneum of continuous ambulatory peritoneal dialysis patients. Pyridoxal 5'-phosphate (PLP), a derivative of vitamin B(6), protects proteins from glycation. Hepatocyte growth factor (HGF) heals damaged tissues in a reciprocal manner against TGF-beta1. First, with the use of gas chromatography-mass spectrometry, whether PLP traps 3-deoxyglucosone (3DG), a major glucose degradation product in PD, was determined. Then, whether rat peritoneal tissue damages induced by intraperitoneal administration of glucose-based PD is ameliorated by PLP or HGF was examined. In vitro incubation with PLP markedly decreased concentration of 3DG in a dose-dependent manner, demonstrating the 3DG-trapping effect of PLP. The peritoneum of PD-treated rats was significantly thickened compared with that of physiologic saline-treated rats. Both PLP and HGF prevented the thickening of rat peritoneum induced by PD and ameliorated accumulation of AGE and expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen and a number of blood vessels. Furthermore, expression of HGF was significantly increased in the peritoneum of PLP-treated rats compared with that of PD-treated rats. In conclusion, PLP shows 3DG-trapping effect. PLP and HGF prevented peritoneal thickening; accumulation of AGE; expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen; and neoangiogenesis in rat peritoneum induced by PD.

Galectin-3/AGE-receptor 3 knockout mice show accelerated AGE-induced glomerular injury: evidence for a protective role of galectin-3 as an AGE receptor

We previously showed that mice lacking galectin-3/AGE-receptor 3 develop accelerated diabetic glomerulopathy. To further investigate the role of galectin-3/AGE-receptor function in the pathogenesis of diabetic renal disease, galectin-3 knockout (KO) and coeval wild-type (WT) mice were injected for 3 months with 30 microg/day of N(epsilon)-carboxymethyllysine (CML)-modified or unmodified mouse serum albumin (MSA). Despite receiving equal doses of CML, KO had higher circulating and renal AGE levels and showed more marked renal functional and structural changes than WT mice, with significantly higher proteinuria, albuminuria, glomerular, and mesangial area and glomerular sclerosis index. Renal 4-hydroxy-2-nonenal content and NFkappaB activation were also more pronounced in KO-CML vs. WT-CML. Kidney mRNA levels of fibronectin, laminin, collagen IV, and TGF-beta were up-regulated, whereas those of matrix metalloproteinase-2 and -14 were down-regulated, again more markedly in KO-CML than WT-CML mice. Basal and CML-induced RAGE and 80K-H mRNA levels were higher in KO vs. WT mice. MSA injection did not produce any significant effect in both genotypes. The association of galectin-3 ablation with enhanced susceptibility to AGE-induced renal disease, increased AGE levels and signaling, and altered AGE-receptor pattern indicates that galectin-3 is operating in vivo as an AGE receptor to afford protection toward AGE-dependent tissue injury.

Advanced glycation end products increase collagen-specific chaperone protein in mouse diabetic nephropathy

Advanced glycation end products (AGEs) appear to contribute to the diabetic complications. This study reports the inhibitory effect of OPB-9195 (OPB), an inhibitor of AGEs formation, and the role of a collagen-specific molecular chaperone, a 47-kDa heat shock protein (HSP47) in diabetic nephropathy. Transgenic mice carrying nitric-oxide synthase cDNA fused with insulin promoter (iNOSTg) leads to diabetes mellitus. The iNOSTg mice at 6 months of age represented diffuse glomerulosclerosis, and the expression of HSP47 was markedly increased in the mesangial area in parallel with increased expression of types I and IV collagens. OPB treatment ameliorated glomerulosclerosis in the iNOSTg mice associated with the decreased expression of HSP47 and types I and IV collagens. The expression of transforming growth factor-beta (TGF-beta) was increased in glomeruli of iNOSTg mice and decreased after treatment with OPB. To confirm these mechanisms, cultured mesangial cells were stimulated with AGEs. AGEs significantly increased the expression of HSP47, type IV collagen, and TGF-beta mRNA. Neutralizing antibody for TGF-beta inhibited the overexpression of both HSP47 and type IV collagen in vitro. In conclusion, AGEs increase the expression of HSP47 in association with collagens, both in vivo and in vitro. The processes may be mediated by TGF-beta.

Cellular Carbonyl Stress Enhances the Expression of Plasminogen Activator Inhibitor-1 in Rat White Adipocytes via Reactive Oxygen Species-dependent Pathway

Carbonyl stress is one of the important mechanisms of tissue damage in vascular complications of diabetes. In the present study, we observed that the plasminogen activator inhibitor-1 (PAI-1) levels in serum and its gene expression in adipose tissue were up-regulated in aged OLETF rats, model animals of obese type 2 diabetes. To study the mechanism of PAI-1 up-regulation, we examined the effect of advanced glycation end products (AGEs) and the product of lipid peroxidation (4-hydroxy-2-nonenal (HNE)), both of which are endogenously generated under carbonyl stress. Stimulation of primary white adipocytes by either AGE or HNE resulted in the elevation of PAI-1 in culture medium and at mRNA levels. The up-regulation of PAI-1 was also observed by incubating the cells in high glucose medium (30 mm, 48 h). The stimulatory effects by AGE or high glucose were inhibited by antioxidant, pyrrolidine dithiocarbamate, and reactive oxygen scavenger, probucol, suggesting a pivotal role of oxidative stress in white adipocytes. We also found that the effect by HNE was inhibited by antioxidant, N-acetylcysteine and that a specific inhibitor of glutathione biosynthesis, l-buthionine-S,R-sulfoximine, augmented the effect of subthreshold effect of HNE. Bioimaging of reactive oxygen species (ROS) by a fluorescent indicator, 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate, revealed ROS production in white adipocytes treated with AGE or HNE. These results suggest that cellular carbonyl stress induced by AGEs or HNE may stimulate PAI-1 synthesis in and release from adipose tissues through ROS formation.

Relation between development of nephropathy and the p22phox C242T and receptor for advanced glycation end product G1704T gene polymorphisms in type 2 diabetic patients

OBJECTIVE

The development of diabetic nephropathy is considered to be associated with oxidative stress. NADPH oxidase and the receptor for advanced glycation end products (RAGE) have attracted attention as mechanisms of generating oxidative stress. We studied the relation between the genotypes of the NADPH p22phox C242T and RAGE G1704T polymorphisms and the development of diabetic nephropathy in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

Using a retrospective review of clinical data, we allocated 181 Japanese type 2 diabetic patients to one of two groups: patients without diabetic nephropathy (group N; n = 108) and patients developing diabetic nephropathy (group D; n = 73) for 10 years or more. The p22phox C242T and RAGE G1704T polymorphisms were examined by Taqman PCR methods.

RESULTS

The frequency of the p22phox CC genotype was significantly higher in group D than in group N (90 vs. 79%; P = 0.0427). The frequency of the RAGE GT + TT genotype was significantly higher in group D than in group N (26 vs. 13%; P = 0.0313). The frequency of the combination of p22phox CC and RAGE GT + TT genotypes was significantly higher in group D than in group N (22 vs. 8%; P = 0.0057). In multiple logistic regression analysis, systolic blood pressure, HbA(1c), triglycerides, and the combination of polymorphisms were shown to be independent variables.

CONCLUSIONS

These results suggest that assessment of the combination of NADPH p22phox C242T and RAGE G1704T polymorphisms may be useful in identifying the risk for developing diabetic nephropathy in type 2 diabetic patients.

A new phloroglucinol derivative from the brown alga Eisenia bicyclis: potential for the effective treatment of diabetic complications

A new phloroglucinol derivative (1) and two known compounds (2 and 3) were isolated from the brown alga Eisenia bicyclis. These isolates exhibit inhibitory activity on glycation and alpha-amylase. Their structures were determined on the basis of spectroscopic data.

Novel inhibitors of advanced glycation endproducts

A number of natural or synthetic compounds as AGE inhibitors have been proposed, discovered or currently being advanced by others and us. We have identified two new classes of aromatic compounds; aryl- (and heterocyclic) ureido and aryl (and heterocyclic) carboxamido phenoxyisobutyric acids, and benzoic acid derivatives and related compounds, as potential inhibitors of glycation and AGE formation. Some of these novel compounds also showed "AGE-breaking" activities in vitro. Current evidence is that chelation of transition metals and/or trapping or indirect inhibition of formation of reactive carbonyl compounds are involved in the mechanisms of action of these novel AGE inhibitors and breakers. Here, we review the inhibitors of glycation and AGE-breakers published to date and present the results of our in vitro and in vivo investigations on a number of these novel AGE inhibitors. These AGE-inhibitors and AGE-breakers may find therapeutic use in the treatment of diseases that AGE formation and accumulation may be responsible for their pathogenesis such as diabetes, Alzheimer's, rheumatoid arthritis, and atherosclerosis.

Inhibition of GAPDH activity by poly(ADP-ribose) polymerase activates three major pathways of hyperglycemic damage in endothelial cells

In this report, we show that hyperglycemia-induced overproduction of superoxide by the mitochondrial electron transport chain activates the three major pathways of hyperglycemic damage found in aortic endothelial cells by inhibiting GAPDH activity. In bovine aortic endothelial cells, GAPDH antisense oligonucleotides activated each of the pathways of hyperglycemic vascular damage in cells cultured in 5 mM glucose to the same extent as that induced by culturing cells in 30 mM glucose. Hyperglycemia-induced GAPDH inhibition was found to be a consequence of poly(ADP-ribosyl)ation of GAPDH by poly(ADP-ribose) polymerase (PARP), which was activated by DNA strand breaks produced by mitochondrial superoxide overproduction. Both the hyperglycemia-induced decrease in activity of GAPDH and its poly(ADP-ribosyl)ation were prevented by overexpression of either uncoupling protein-1 (UCP-1) or manganese superoxide dismutase (MnSOD), which decrease hyperglycemia-induced superoxide. Overexpression of UCP-1 or MnSOD also prevented hyperglycemia-induced DNA strand breaks and activation of PARP. Hyperglycemia-induced activation of each of the pathways of vascular damage was abolished by blocking PARP activity with the competitive PARP inhibitors PJ34 or INO-1001. Elevated glucose increased poly(ADP-ribosyl)ation of GAPDH in WT aortae, but not in the aortae from PARP-1-deficient mice. Thus, inhibition of PARP blocks hyperglycemia-induced activation of multiple pathways of vascular damage.

Intervention against the Maillard reaction in vivo

The field of Maillard/glycation reactions in vivo has grown enormously during the past 20 years, going from 25 to 500 publications per year. It is now well recognized that many of the "advanced" products form oxidatively or anaerobically and can have deleterious effects on macromolecular and biological function. The feasibility of developing pharmacological agents with beneficial in vivo properties, based on in vitro inhibition of glycation, has been surprisingly successful. This Editorial sets the stage for a series of articles by experts in the field, who have made key contributions to our understanding of the Maillard reaction in vivo.

Rapid suppression of mitochondrial permeability transition by methylglyoxal. Role of reversible arginine modification

Methylglyoxal (MG) (pyruvaldehyde) is a reactive carbonyl compound produced in glycolysis. MG can form covalent adducts on proteins resulting in advanced glycation end products that may alter protein function. Here we report that MG covalently modifies the mitochondrial permeability transition pore (PTP), a high conductance channel involved in the signal transduction of cell death processes. Incubation of isolated mitochondria with MG for a short period of time (5 min), followed by removal of excess free MG, prevented both ganglioside GD3- and Ca2+-induced PTP opening and the ensuing membrane depolarization, swelling, and cytochrome c release. Under these conditions MG did not significantly interfere with mitochondrial substrate transport, respiration, or oxidative phosphorylation. The suppression of permeability transition was reversible following extended incubation in MG-free medium. Of the 29 physiological carbonyl and dicarbonyl compounds tested only MG and its analogue glyoxal were able to specifically alter the behavior of the PTP. Using a set of arginine-containing peptides, we found that the major MG-derived arginine adduct formed, following a short time exposure to MG, was the 5-hydro-5-methylimidazol-4-one derivative. These findings demonstrate that MG rapidly modifies the PTP covalently and stabilizes the PTP in the closed conformation. This is probably due to the formation of an imidazolone adduct on an arginine residue involved in the control of PTP conformation (Linder, M. D., Morkunaite-Haimi, S., Kinnunen, P. J. K., Bernardi, P., and Eriksson, O. (2002) J. Biol. Chem. 277, 937-942). We deduce that the permeability transition constitutes a potentially important physiological target of MG.

Glucose, glycation, and RAGE: implications for amplification of cellular dysfunction in diabetic nephropathy

Receptor for advanced glycation endproducts (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Driven by rapid accumulation and expression of key ligands such as advanced glycation endproducts (AGE) and S100/calgranulins in diabetic tissues, upregulation and activation of RAGE magnifies cellular perturbation in tissues affected by hyperglycemia, such as the large blood vessels and the kidney. In the diabetic glomerulus, RAGE is expressed principally by glomerular visceral epithelial cells (podocytes). Blockade of RAGE in the hyperglycemic db/db mouse suppresses functional and structural alterations in the kidney, in the absence of alterations in blood glucose. Recent studies in homozygous RAGE null mice support a key role for RAGE in glomerular perturbation in diabetes. Importantly, beyond diabetes, studies in other settings of glomerulopathies support a critical RAGE-dependent pathway in podocytes linked to albuminuria, mesangial expansion, and glomerular sclerosis. A new paradigm is proposed in glomerular injury, and it is suggested that blockade of the RAGE axis may provide a novel means to prevent irreparable glomerular injury in diabetes and other sclerosing glomerulopathies.

Anti-hypertensive agents inhibit in vivo the formation of advanced glycation end products and improve renal damage in a type 2 diabetic nephropathy rat model

Prevention or retardation of diabetic nephropathy (DN) includes anti-hypertensive treatment with angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II type 1 receptor blockers (ARB) on the premises that these drugs have an added protective effect beyond their influence on BP. The present study used a strain of spontaneously hypertensive/NIH-corpulent rats [SHR/NDmc-cp (fat/fat)] as a model of type II DN to unravel the renoprotective effects of anti-hypertensive drugs. Olmesartan (1 or 5 mg/kg per d), an ARB, and hydralazine (5mg/kg per d), an anti-hypertensive drug without effect on the renin-angiotensin system (RAS), were given for 20 wk. BP, renal function, glucose and insulin levels, and proteinuria were monitored. Glomerular lesions and kidney pentosidine content were assessed at the end of the study. Olmesartan (1 and 5 mg) significantly reduced BP and kidney pentosidine content and improved histologic renal damage and proteinuria. The changes were dose-dependent. The effect of hydralazine (5 mg) was similar to that of olmesartan (1 mg) but reached statistical significance only for kidney pentosidine content. The similarity of both drugs' effects on kidney damage and proteinuria suggest that renoprotection does not hinge on manipulation of RAS in these rats. By contrast, the inhibition of renal pentosidine formation assessed both by immunohistochemistry and HPLC suggests a critical role of advanced glycation end product (AGE) formation together with hypertension in the genesis of diabetic nephropathy. This view is supported by the correlation found between renal pentosidine content and proteinuria. The unsuspected AGE-lowering effect of hydralazine was further confirmed in vitro and elucidated; it is due to both reactive carbonyl compounds trapping and modifications of the oxidative metabolism. It is concluded that AGE inhibition should be included in the therapeutic strategy of DN.

Two flavone C-glycosides from the style of Zea mays with glycation inhibitory activity

A new flavone C-glycoside, chrysoeriol 6-C-beta-boivinopyranosyl-7-O-beta-glucopyranoside (1), and a known flavone C-glycoside (2) were isolated from the style of Zea mays. Each compound contains the rare sugar boivinose. These flavones exhibited glycation inhibitory activity similar to that of aminoguanidine, a known glycation inhibitor.

Benfotiamine blocks three major pathways of hyperglycemic damage and prevents experimental diabetic retinopathy

Three of the major biochemical pathways implicated in the pathogenesis of hyperglycemia induced vascular damage (the hexosamine pathway, the advanced glycation end product (AGE) formation pathway and the diacylglycerol (DAG)-protein kinase C (PKC) pathway) are activated by increased availability of the glycolytic metabolites glyceraldehyde-3-phosphate and fructose-6-phosphate. We have discovered that the lipid-soluble thiamine derivative benfotiamine can inhibit these three pathways, as well as hyperglycemia-associated NF-kappaB activation, by activating the pentose phosphate pathway enzyme transketolase, which converts glyceraldehyde-3-phosphate and fructose-6-phosphate into pentose-5-phosphates and other sugars. In retinas of diabetic animals, benfotiamine treatment inhibited these three pathways and NF-kappaB activation by activating transketolase, and also prevented experimental diabetic retinopathy. The ability of benfotiamine to inhibit three major pathways simultaneously might be clinically useful in preventing the development and progression of diabetic complications.

Advanced glycation end products inhibit de novo protein synthesis and induce TGF-beta overexpression in proximal tubular cells

BACKGROUND

We have shown previously that OPB-9195, a novel inhibitor of advanced glycation end products (AGE), significantly prevented renal tubular injury and tubulointerstitial fibrosis in spontaneous diabetic rats. However, the molecular mechanisms underlying this have not been fully elucidated.

METHODS

Three immunochemically distinct AGE were prepared by incubating bovine serum albumin (BSA) with glucose, glyceraldehyde, or methylglyoxal. Then, the effects of AGE on human proximal tubular epithelial cells were examined. The intracellular formation of reactive oxygen species (ROS) was detected using the fluorescent probe CM-H2DCFDA. DNA synthesis was evaluated by thymidine uptake, and de novo protein synthesis was determined by [3H]leucine incorporation. Prostaglandin E2 (PGE2) and transforming growth factor-beta (TGF-beta) released into media were quantitatively analyzed in an enzyme-linked immunosorbent assay. TGF-beta gene expression was analyzed by quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

When these AGE-BSA were administered to tubular cells, each of them increased generation of intracellular ROS. All of the AGE-BSA, but not non-glycated BSA, were found to induce statistically significant decreases in de novo protein synthesis and PGE2 secretion by tubular cells. Furthermore, AGE-BSA up-regulated the levels of mRNAs for TGF-beta in tubular cells. The structural epitope designated glucose-derived AGE was found to have the greatest cytopathic effects on tubular cells. These AGE-induced inhibition of protein synthesis and PGE2 secretion as well as the up-regulation of TGF-beta mRNA were found to be completely prevented by N-acetylcysteine. Furthermore, H2O2 was shown to inhibit protein synthesis and PGE2 secretion by proximal tubular cells in a dose-dependent manner.

CONCLUSION

The results suggest that AGE inhibits de novo protein synthesis and stimulates TGF-beta mRNA expression in proximal tubular epithelial cells through overgeneration of intracellular ROS. Thus, AGE are involved in the pathogenesis of tubular injury in diabetic nephropathy.

Modulation of heat-shock protein 27 (Hsp27) anti-apoptotic activity by methylglyoxal modification

Methylglyoxal (MG) is one of the side-products in glycolysis, and it reacts with proteins under physiological conditions. Here, we identified heat-shock protein 27 (Hsp27) as a major MG-modified protein in cells. MG modification of Hsp27 selectively occurs at Arg-188 to form argpyrimidine, and mutation in the residue represses the formation of a large oligomer. This modification process is essential to its repressing activity for cytochrome c-mediated caspase activation. Inhibition of MG modification of Hsp27 causes sensitization of the cells to anti-tumor drug-induced apoptosis. Thus, MG is a novel modulator of cell survival by directly incorporating with the specific protein residue.

ALT-946 and aminoguanidine, inhibitors of advanced glycation, improve severe nephropathy in the diabetic transgenic (mREN-2)27 rat

The severe diabetic nephropathy that develops in the hypertensive transgenic (mRen-2)27 rat with streptozotocin (STZ) diabetes has previously been considered angiotensin II-dependent. Because metabolic pathways are also activated in the diabetic kidney, the present study aimed to determine whether renoprotection could be afforded with inhibitors of advanced glycation end products (AGEs), ALT-946, and aminoguanidine (AG). At 6 weeks of age, nondiabetic control and STZ diabetic Ren-2 rats were randomized to receive vehicle, ALT-946 (1 g/l), or AG (1 g/l) and were studied for 12 weeks. Systolic blood pressure was unchanged with diabetes, ALT-946, or AG. Both kidney weight and glomerular filtration rate were increased with diabetes and unchanged with ALT-946 or AG. ALT-946 and AG equally ameliorated glomerulosclerosis and medullary pathology; however, ALT-946 did reduce cortical tubular degeneration to a greater extent than AG. Albumin excretion rate, which was elevated with diabetes, was reduced with ALT-946 but not AG. AGE immunolabeling was increased in glomeruli and reduced with ALT-946 and AG. These findings indicate that even in the context of renal injury presumed to be primarily blood pressure- and/or angiotensin II-dependent, approaches that interfere with metabolic pathways such as inhibitors of AGE formation can confer renal protection in experimental diabetes.

Angiotensin II receptor antagonists and angiotensin-converting enzyme inhibitors lower in vitro the formation of advanced glycation end products: biochemical mechanisms

The implication of advanced glycation end products (AGE) in the pathogenesis of atherosclerosis and of diabetic and uremic complications has stimulated a search for AGE inhibitors. This study evaluates the AGE inhibitory potential of several well-tolerated hypotensive drugs. Olmesartan, an angiotensin II type 1 receptor (AIIR) antagonist, as well as temocaprilat, an angiotensin-converting enzyme (ACE) inhibitor, unlike nifedipine, a calcium blocker, inhibit in vitro the formation of two AGE, pentosidine and N(epsilon)-carboxymethyllysine (CML), during incubation of nonuremic diabetic, nondiabetic uremic, or diabetic uremic plasma or of BSA fortified with arabinose. This effect is shared by all tested AIIR antagonists and ACE inhibitors. On an equimolar basis, they are more efficient than aminoguanidine or pyridoxamine. Unlike the latter two compounds, they do not trap reactive carbonyl precursors for AGE, but impact on the production of reactive carbonyl precursors for AGE by chelating transition metals and inhibiting various oxidative steps, including carbon-centered and hydroxyl radicals, at both the pre- and post-Amadori steps. Their effect is paralleled by a lowered production of reactive carbonyl precursors. Finally, they do not bind pyridoxal, unlike aminoguanidine. Altogether, this study demonstrates for the first time that widely used hypotensive agents, AIIR antagonists and ACE inhibitors, significantly attenuate AGE production. This study provides a new framework for the assessment of families of AGE-lowering compounds according to their mechanisms of action.

Advanced glycation end products and diabetic complications

Diabetic complications are major cause of morbidity and mortality in patients with diabetes. While the precise pathogenic mechanism(s) underlying conditions such as diabetic retinopathy, diabetic nephropathy and increased risk of atherosclerosis remain ill-defined, it is clear that hyperglycaemia is a primary factor that initiates and promotes complications. Formation of advanced glycation end products (AGEs) correlate with glycaemic control, and these reactive adducts form on DNA, lipids and proteins where they represent pathophysiological modifications that precipitate dysfunction at a cellular and molecular level. Many of these adducts form rapidly during diabetes and promote progression of a raft of diabetes-related complications. Recent evidence also suggests an important interaction with other pathogenic mechanisms activated within the diabetic milieu. This review outlines the nature of AGE formation in biological systems and highlights accumulative evidence that implicates these adducts in diabetic complications. As more therapeutic agents are developed to inhibit AGE formation or limit their pathogenic influence during chronic diabetes, it is becoming clear that these anti-AGE strategies have an important role to play in the treatment of diabetic patients.

Prevention of diabetic nephropathy in mice by a diet low in glycoxidation products

BACKGROUND

Reactive advanced glycation end products (AGEs), known to promote diabetic tissue damage, occur endogenously as well as in heated foods and are orally absorbed. The relative contribution of diet-derived AGEs to diabetic nephropathy (DN) remains unclear.

METHODS

We tested a standard mouse food (AIN-93G) found to be rich in AGEs (H-AGE diet) in parallel with a similar diet that contained six-fold lower AGE content (L-AGE), but equal calories, macronutrients, and micronutrients. Non-obese diabetic mice (NOD) with type 1 diabetes (T1D) and db/db mice with type 2 diabetes (T2D) were randomly assigned to each formula for either 4 or 11 months, during which time renal parameters and AGE levels were assessed.

RESULTS

Compared to the progressive DN and short survival seen in NOD mice exposed to long-term H-AGE feeding, L-AGE-fed NOD mice developed minimal glomerular pathology and a modest increase in urinary albumin:creatinine ratio (p<0.005), and a significantly extended survival (p<0.0001), consistent with lower serum (p<0.025) and kidney AGEs (p<0.01). Also, in the 4-month study, and in contrast to the H-AGE-fed mice, L-AGE-fed NOD and db/db mice exhibited low levels of renal cortex TGF beta-1 (p<0.05), laminin B1 mRNA (p<0.01) and alpha 1 IV collagen mRNA (p<0.05) and protein, in concert with reduced serum and kidney AGEs (p<0.05, respectively).

CONCLUSION

Intake of high-level, food-derived AGEs is a major contributor to DN in T1D and T2D mice. Avoidance of dietary AGEs provides sustained protection against DN in mice; providing the rationale for similar studies in human diabetic patients.

Pyridoxamine inhibits early renal disease and dyslipidemia in the streptozotocin-diabetic rat

BACKGROUND

Nonenzymatic reactions between sugars or lipids and protein and formation of advanced glycation and lipoxidation end products (AGE/ALEs) contribute to the chemical modification and cross-linking of tissue proteins with age. Accelerated formation of AGE/ALEs during hyperglycemia is implicated in the development of diabetic complications. In this study, we examined the effect of the AGE/ALE inhibitor pyridoxamine on chemical modification and cross-linking of collagen and development of renal disease in the streptozotocin-diabetic rat.

METHODS

Diabetic rats were treated with pyridoxamine; parallel experiments were conducted with aminoguanidine, the prototype AGE inhibitor. Progression of renal disease was evaluated by measurements of albuminuria and plasma creatinine concentration. Plasma triglycerides, cholesterol, lactate and pyruvate were measured by enzymatic assays, and AGE/ALEs in skin collagen by HPLC and GC-MS assays.

RESULTS

Pyridoxamine significantly inhibited the increase in albuminuria, plasma creatinine, hyperlipidemia and plasma lactate/pyruvate ratio in diabetic rats, without an effect on blood glucose or glycated hemoglobin. AGE/ALEs, fluorescence and cross-linking of skin collagen increased approximately twofold in diabetic versus control rats after seven months of diabetes. Pyridoxamine caused a significant (25 to 50%) decrease the AGE/ALEs, carboxymethyllysine and carboxyethyllysine, cross-linking and fluorescence in skin collagen of diabetic rats, but did not affect pentosidine.

CONCLUSIONS

Pyridoxamine inhibits the progression of renal disease, and decreases hyperlipidemia and apparent redox imbalances in diabetic rats. Pyridoxamine and aminoguanidine had similar effects on parameters measured, supporting a mechanism of action involving AGE/ALE inhibition.

Diabetes and advanced glycation endproducts

Bio-reactive advanced glycation endproducts (AGE) alter the structure and function of molecules in biological systems and increase oxidative stress. These adverse effects of both exogenous and endogenously derived AGE have been implicated in the pathogenesis of diabetic complications and changes associated with ageing including atherosclerosis, renal, eye and neurological disease. Specific AGE receptors and nonreceptor mechanisms contribute to these processes but also assist in the removal and degradation of AGE. The final disposal of AGE depends on renal clearance. Promising pharmacologic strategies to prevent AGE formation, reduce AGE toxicity, and/or inactivate AGE are under investigation.

Podocyte injury promotes progressive nephropathy in zucker diabetic fatty rats

The zucker diabetic fatty (ZDF-fa/fa) rat is one of the attractive models for type II diabetes based on impaired glucose tolerance caused by the inherited insulin-resistance gene fa. Characterization of nephropathy in this model may provide useful insights into the mechanism of the progression of diabetic nephropathy. The present study analyzed the pathophysiology of diabetes and nephropathy, including the process of glomerulosclerosis in this model by biochemical and morphometric analyses. In addition, we conducted studies in podocytes in culture to examine the direct effects of high glucose on podocytes. ZDF-fa/fa rats showed overt diabetes despite hyperinsulinemia as early as 3 months of age. Blood glucose levels increased further with a considerable decrease of insulin levels at 5 months. Glomerular filtration rate (GFR) was significantly elevated until 3 months, but fell to the level seen in lean rats by 7 months. Proteinuria started to rise during the period of increased GFR, and increased further after GFR had fallen to within the normal range. Renal fibronectin, collagen iv, and vascular endothelial growth factor mRNA levels were increased at 7 months. Glomerulosclerosis commenced as early as 5 months of age, and was associated with glomerular hypertrophy and mild mesangial expansion with evidence of accentuated podocyte injury, as revealed by increased expression of desmin. Electron microscopy suggested that degeneration of podocytes and the development of tuft adhesions were responsible for the glomerular sclerosis in this model. In addition, glomeruli from the diabetic rats showed up-regulation of the cyclin kinase inhibitors, p21 and p27. Further studies suggested that the increase in p27 expression was predominantly caused by podocytes, because predominant immunolocalization of p27 in podocytes in diabetic rats and high glucose medium induced cell hypertrophy accompanied by p27 up-regulation in differentiated podocyte cell lines. In conclusion, progressive diabetic nephropathy in ZDF-fa/fa rats is associated with evidence of podocyte injury. High concentrations of ambient glucose induced podocyte hypertrophy and stress in vitro, suggesting that the podocyte is a likely target of the diabetic milieu.

Chelating activity of advanced glycation end-product inhibitors

The advanced glycation end-product (AGE) hypothesis proposes that accelerated chemical modification of proteins by glucose during hyperglycemia contributes to the pathogenesis of diabetic complications. The two most commonly measured AGEs, N(epsilon)-(carboxymethyl)lysine and pentosidine, are glycoxidation products, formed from glucose by sequential glycation and autoxidation reactions. Although several compounds have been developed as AGE inhibitors and are being tested in animal models of diabetes and in clinical trials, the mechanism of action of these inhibitors is poorly understood. In general, they are thought to function as nucleophilic traps for reactive carbonyl intermediates in the formation of AGEs; however alternative mechanisms of actions, such as chelation, have not been rigorously examined. To distinguish between the carbonyl trapping and antioxidant activity of AGE inhibitors, we have measured the chelating activity of the inhibitors by determining the concentration required for 50% inhibition of the rate of copper-catalyzed autoxidation of ascorbic acid in phosphate buffer. All AGE inhibitors studied were chelators of copper, as measured by inhibition of metal-catalyzed autoxidation of ascorbate. Apparent binding constants for copper ranged from approximately 2 mm for aminoguanidine and pyridoxamine, to 10-100 microm for carnosine, phenazinediamine, OPB-9195 and tenilsetam. The AGE-breakers, phenacylthiazolium and phenacyldimethylthiazolium bromide, and their hydrolysis products, were among the most potent inhibitors of ascorbate oxidation. We conclude that, at millimolar concentrations of AGE inhibitors used in many in vitro studies, inhibition of AGE formation results primarily from the chelating or antioxidant activity of the AGE inhibitors, rather than their carbonyl trapping activity. Further, at therapeutic concentrations, the chelating activity of AGE inhibitors and AGE-breakers may contribute to their inhibition of AGE formation and protection against development of diabetic complications.

Biochemistry and molecular cell biology of diabetic complications

Diabetes-specific microvascular disease is a leading cause of blindness, renal failure and nerve damage, and diabetes-accelerated atherosclerosis leads to increased risk of myocardial infarction, stroke and limb amputation. Four main molecular mechanisms have been implicated in glucose-mediated vascular damage. All seem to reflect a single hyperglycaemia-induced process of overproduction of superoxide by the mitochondrial electron-transport chain. This integrating paradigm provides a new conceptual framework for future research and drug discovery.

Glycoxidation-modified macrophages and lipid peroxidation products are associated with the progression of human diabetic nephropathy

The aim of this study is to investigate the role of glomerular macrophages activated by glycoxidation and lipid peroxidation products in the progression of glomerular lesions in diabetic nephropathy. Renal biopsy samples from 43 patients with diabetes (age, 54 +/- 14 years) and 10 control cases were immunohistochemically examined for the expression of carboxymethyllysine (CML), a representative glycoxidative product; oxidized phosphatidylcholine (Ox-PC), a representative lipid peroxidation product; leukocyte common antigen (LCA); CD68; and macrophage scavenger receptor (MSR) class A. The severity of the diffuse lesions in each glomerulus was histologically graded from 0 to IV. When grade II and III lesions had Kimmelstiel-Wilson (KW) nodules, they were placed in a new category called grade III with KW nodules. The number of cells positive for CML, Ox-PC, LCA, CD68, and MSR was compared in different grades. The number of macrophages per glomerulus increased with the glomerular lesion grade and was highest in grade III with KW nodules. Conversely, the number of lymphocytes did not parallel the grade of glomerular lesions. Almost 50% of macrophages contained CML, and more than 40% of those were observed in exudative lesions, tuft adhesions, and at the periphery of KW nodules. Ox-PC accumulated in 50% of CML-positive macrophages, which coexpress MSR. Macrophages positive for CML and Ox-PC increased with the grade. Glomerular macrophages may be activated by glycoxidative and lipid peroxidation products through MSR and may have a role in the development of human diabetic glomerulosclerosis.

Combating diabetic nephropathy with drug therapy

Diabetes mellitus is the leading cause of end-stage renal disease and also increases the risk of atherosclerotic vascular disease. Hypertension amplifies both problems. Detection of microalbuminuria, a common and early manifestation of diabetic nephropathy and a marker for cardiovascular risk, permits early treatment to reduce progression of nephropathy and vascular disease in diabetes. Although optimal glycemic control is essential to reduce the risk of nephropathy, aggressive blood pressure lowering to a level of 130/80 mg Hg or below in hypertensive diabetic patients is as important as glycemic control. Initial drug therapy for nephropathy should include an angiotensin-converting enzyme inhibitor (or if contra-indicated, an angiotensin receptor blocker), as several large randomized double-blinded multicenter clinical trials have demonstrated an independent renoprotective effect with renin angiotensin system inhibition. The role of advanced glycation end products in the pathogenesis of renal and vascular disease in diabetes is becoming more clearly established. However, the use of therapeutic strategies directed at blocking their effect still awaits further investigation. A multifaceted intervention program that combines optimal glycemic control, lifestyle modification/cardiovascular prevention guidelines such as lipid control and smoking cessation, with appropriate antihypertensive therapy when indicated, will prevent or delay both the occurrence and progression of diabetic nephropathy.

Development and prevention of advanced diabetic nephropathy in RAGE-overexpressing mice

Vascular complications arising from multiple environmental and genetic factors are responsible for many of the disabilities and short life expectancy associated with diabetes mellitus. Here we provide the first direct in vivo evidence that interactions between advanced glycation end products (AGEs; nonenzymatically glycosylated protein derivatives formed during prolonged hyperglycemic exposure) and their receptor, RAGE, lead to diabetic vascular derangement. We created transgenic mice that overexpress human RAGE in vascular cells and crossbred them with another transgenic line that develops insulin-dependent diabetes shortly after birth. The resultant double transgenic mice exhibited increased hemoglobin A(1c) and serum AGE levels, as did the diabetic controls. The double transgenic mice demonstrated enlargement of the kidney, glomerular hypertrophy, increased albuminuria, mesangial expansion, advanced glomerulosclerosis, and increased serum creatinine compared with diabetic littermates lacking the RAGE transgene. To our knowledge, the development of this double transgenic mouse provides the first animal model that exhibits the renal changes seen in humans. Furthermore, the phenotypes of advanced diabetic nephropathy were prevented by administering an AGE inhibitor, (+/-)-2-isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetanilide (OPB-9195), thus establishing the AGE-RAGE system as a promising target for overcoming this aspect of diabetic pathogenesis.