Enhanced cellular oxidant stress by the interaction of advanced glycation end products with their receptors/binding proteins

Advanced glycation end products impair protein turnover in LLC-PK1: amelioration by trypsin

BACKGROUND

Advanced glycation end products (AGEs) are assumed to play a key role in the pathogenesis of diabetic nephropathy (DN) and other diabetic complications. While AGEs have been shown to exert marked effects on mesangial and endothelial cells as well as on monocytes/macrophages, little is known about their effects on tubule cells. Therefore, we addressed the questions of (1) whether AGE-bovine serum albumin (AGE-BSA) impairs the protein metabolism in the tubule cells, and if so, (2) whether the AGE-induced effects are mediated via a protease sensitive mechanism.

METHODS

Arrested LLC-PK1 cells were exposed to a medium containing the vehicle (control, serum free), AGE-BSA (38 micromol/L), or BSA (38 micromol/L) in the presence or absence of trypsin (2.5 microg/mL) for 24 hours. We evaluated cell number, cell size, and cell protein content, as well as protein synthesis and protein degradation.

RESULTS

After an incubation period of 24 hours, AGE-BSA decreased the cell number to 84.5 +/- 5.5% of control and 82.5 +/- 5.6% of BSA-treated cells (P < 0.05). [3H]-thymidine incorporation declined to 66% of control (P < 0.05), while BSA was without any effect. The same AGE-BSA dose reduced protein degradation (P < 0.05) and stimulated total protein synthesis slightly, as determined by L-[14C]Phe incorporation into acidic-insoluble proteins. These effects resulted in a rise in cell protein content (AGE-BSA vs. control, 21.9 +/- 6.7%; AGE-BSA vs. BSA, 11.1 +/- 6.0%, P < 0.05) and cell volume (AGE-BSA vs. control 9.4 +/- 3.2%, AGE-BSA vs. BSA 18.4 +/- 3.7%, P < 0.05). Coincubation with AGE-BSA and trypsin was associated with an amelioration of all investigated parameters concerning cell number, cell proliferation, raised cell protein content, decreased protein degradation, and enhanced protein synthesis.

CONCLUSION

These data indicate that AGE-BSA impairs cell proliferation and protein turnover in LLC-PK1 cells with a consequent rise in cell protein. Since these alterations were abrogated by coincubation with trypsin, an interference of this serine protease with the AGE-binding proteins on cell surfaces is assumed.

Inflammation and advanced glycation end products in uremia: simple coexistence, potentiation or causal relationship?

The causes for the high frequency of cardiovascular disease in dialysis patients are multifactorial in origin. Disturbances in the carbohydrate and lipid metabolism, the balance between oxidants and antioxidants and the immuno-inflammatory system are thought to play a role. Chronic uremia is characterized by the accumulation of advanced glycation end products (AGEs) and advanced oxidation products (AOPP) as well as activation of the acute phase response. High serum levels of these products and acute phase reactants such as C-reactive protein (CRP), fibrinogen and serum amyloid A can be found. CRP has been shown to predict cardiovascular and overall mortality in hemodialysis patients. Whether CRP is involved causally in atherosclerosis or merely represents a marker of disease is as yet unknown. Since CRP has been detected in colocalization with modified apolipoproteins or complement components in atherosclerotic lesions, a pathophysiological role seems very likely. AGEs as well have been detected in aortas of hemodialysis patients. Incubation of endothelial cells with AGEs induced expression of adhesion molecules with consecutive attraction of monocytes to the vessel wall. Thus far, clinical studies investigating the predictive effects of AGEs on cardiovascular mortality in hemodialysis patients are lacking. There is considerable debate about what factors turn on the acute phase response in this population. Proinflammatory effects of AGEs mediated through one receptor for AGEs, RAGE, have been described. We hypothesize that there may be a link between increased hepatic CRP production and the accumulation of AGEs in uremia. AGEs may stimulate CRP production in hepatocytes either directly or indirectly via interaction with monocytes.

Reactive carbonyl compounds related uremic toxicity ("carbonyl stress")

Many studies on uremic toxins have focused on enzymatic biochemistry. Recently, attention has turned to nonenzymatic biochemistry, especially progressive and irreversible modifications of proteins. Two different approaches opened the field of irreversible nonenzymatic modifications of proteins in uremia: the advanced glycation end products (AGEs) derived from the Maillard reaction and the advanced lipoxidation end products (ALEs) derived from lipid peroxidation. They have revealed the accumulation of reactive carbonyl compounds (RCOs) derived from carbohydrates and lipids and the subsequent carbonyl modifications of proteins ("carbonyl stress"). In this article, we describe the causal role of various RCOs and AGEs/ALEs accumulating in uremia, the clinical consequences of carbonyl stress in uremia, and finally, the therapeutic perspectives. We propose carbonyl stress as a new uremic toxicity.

Role of iron in progressive renal disease

The importance of iron in renal injury is derived from the ease with which iron is reversibly oxidized or reduced, enabling it to participate in the production of free radicals. Experimental evidence for the role of oxidants and iron in progressive renal disease falls into two broad categories. First, considerable data implicate oxidants in the proteinuria of glomerular disease. To the extent that proteinuria is an important determinant of progression, reduction of proteinuria would result in retardation of progression. Evidence also suggests a role of oxidants and iron in diabetic nephropathy, a major cause of end-stage kidney disease. Second, more direct studies have examined the role of oxidants and iron in models of progressive renal disease. These studies include the demonstration of increased iron in the kidney in models of progressive kidney disease; enhanced generation of oxidants, providing a mechanism by which iron can be mobilized; and more direct evidence of the beneficial effect of iron-deficient diets and iron chelators. Although the collective information on the role of oxidants and iron derived from in vitro studies and animal models of glomerular disease and progressive renal failure is impressive, control studies of patients are needed to show the efficacy of antioxidants and/or iron chelators in retarding the progression of renal failure and may offer an important therapeutic modality to patients with renal disease.

Coregulation of neurite outgrowth and cell survival by amphoterin and S100 proteins through receptor for advanced glycation end products (RAGE) activation

Amphoterin is a protein enhancing process extension and migration in embryonic neurons and in tumor cells through binding to receptor for advanced glycation end products (RAGE), a multiligand transmembrane receptor. S100 proteins, especially S100B, are abundantly expressed in the nervous system and are suggested to function as cytokines with both neurotrophic and neurotoxic effects. However, the cell surface receptor for the cytokine function of S100B has not been identified. Here we show that two S100 family proteins, S100B and S100A1, activate RAGE in concert with amphoterin inducing neurite outgrowth and activation of transcription factor NF-kappaB. Furthermore, activation of RAGE by amphoterin and S100B promotes cell survival through increased expression of the anti-apoptotic protein Bcl-2. However, whereas nanomolar concentrations of S100B induce trophic effects in RAGE-expressing cells, micromolar concentrations of S100B induce apoptosis in an oxidant-dependent manner. Both trophic and toxic effects are specific for cells expressing full-length RAGE since cells expressing a cytoplasmic domain deletion mutant of RAGE are unresponsive to these stimuli. These findings suggest that activation of RAGE by multiple ligands is able to promote trophic effects whereas hyperactivation of RAGE signaling pathways promotes apoptosis. We suggest that RAGE is a signal-transducing receptor for both trophic and toxic effects of S100B.

Influence of diabetes on cardiac nitric oxide synthase expression and activity

There is some evidence that the endothelium dependent vasodilatation of coronary arteries is impaired in both types of diabetes. The underlying mechanisms are not yet clear, in particular whether this defect is caused by a direct effect of diabetes on the activity and the expression of nitric oxide synthases (NOS) or indirectly by an enhanced inactivation of nitric oxide.

METHODS

To study this question we determined the activity (conversion of L-arginine to citrulline) and the mRNAs encoding the isoforms of NOS (using polymerase chain reaction after reverse transcription of the mRNAs into cDNAs by reverse transcriptase) in hearts of streptozotocin diabetic rats and in rat heart endothelial cells (RHEC). The formation of reactive oxygen intermediates (ROI) was measured by the dichloro-dihydro-fluorescein method.

RESULTS

The activity of total NOS and the amounts of mRNAs encoding ecNOS and iNOS were dependent on the duration of diabetes. After a diabetes duration of 4 to 6 weeks both the total activity as well as the mRNAs encoding ecNOS and iNOS were elevated. A reduction of NOS activity and the amounts of mRNAs of ecNOS and iNOS was only seen after a diabetes duration longer than 20 weeks, a time at which a loss of endothelium has been described. In RHEC, high glucose (22 mM) and H(2)O(2) (100 microM) were able to increase the mRNA encoding ecNOS, but not iNOS. This increase in ecNOS mRNA was inhibited by lipoic acid (1 microM). In addition, high glucose (22 and 30 mM) led to an enhanced formation of ROI and to activation of the transcription NF kappa B.

CONCLUSION

These observations suggest that diabetes causes a temporary increase in NOS activity and ecNOS mRNA in the rat heart which is presumably the consequence of an enhanced oxidative stress exerted by hyperglycaemia. Together with previously published observations, our data suggest that the impairment of endothelium dependent vasodilatation in rat heart is not the consequence of a reduced activity and expression of NOS, but is caused by an enhanced inactivation of nitric oxide by ROI.

Crosslinking of alpha-synuclein by advanced glycation endproducts--an early pathophysiological step in Lewy body formation?

An excess of reactive carbonyl compounds (carbonyl stress) and their reaction products, advanced glycation endproducts (AGEs), are thought to play a decisive role in the pathogenesis of neurodegenerative disorders and Parkinson's disease (PD) in particular. Accumulation of AGEs in various intracellular pathological hallmarks of PD, such as Lewy bodies, densely crosslinked intracellular protein deposits formed from neurofilament components and alpha-synuclein, have already been described in patients in advanced stages of the disease. There is, however, no indication of the involvement of AGE-induced crosslinking of alpha-synuclein in very early stages of the disease. In this study, we observed that AGEs and alpha-synuclein are similarly distributed in very early Lewy bodies in the human brain in cases with incidental Lewy body disease. These cases might be viewed as pre-Parkinson patients, i.e. patients who came for autopsy before the possible development of clinical signs of PD. AGEs are both markers of transition metal induced oxidative stress as well as, inducers of protein crosslinking and free radical formation by chemical and cellular processes. Thus, it is likely that AGE promoted formation of Lewy bodies reflects very early causative changes rather than late epiphenomenons of PD.

Inhibition of nitric oxide synthase activity by early and advanced glycation end products in cultured rabbit proximal tubular epithelial cells

Nitric oxide (NO) is important in the regulation of renal tubular function. We have investigated whether glycated proteins could impair the NO production by examining the effects of Amadori products (AP-BSA) and advanced glycation end products (AGE-BSA) on primary cultures of rabbit proximal tubular epithelial (PTE) cells. Nitric oxide synthase activity was assessed by measurement of the conversion of L-arginine to L-citrulline and by production of NO, after short-term (30 min) or long-term (1 or 3 days) incubation. Short incubations of PTE cells with either 200 microg/ml AP-BSA or 40 microg/ml AGE-BSA significantly decreased NO production. AP-BSA (3000 microg/ml) inhibited the Ca(2+)-dependent NOS activity even though above 50 microg/ml it increased Ca(2+)-independent NOS activity. In contrast, 40 microg/ml AGE-BSA inhibited both isoforms of NOS. Longer incubations with 200 microg/ml AP-BSA or 250 microg/ml AGE-BSA decreased NO release and inhibited Ca(2+)-dependent and -independent NOS activities. APs did not affect NO release by S-nitroso-N-acetyl-penicillamine (SNAP), while 250 microg/ml AGEs decreased it. After 3 days incubation, glycation products had no effect on the NOS cell content. Cell viability and proliferation were not modified under these experimental conditions, suggesting that the fall in NO production was not due to there being fewer cells. These data indicate that APs and AGEs directly inhibit NOS activity, and additionally that AGEs quench released NO. Thus, both types of glycated proteins alter the production of NO by PTE cells and could participate in the renal tubule dysfunction associated with aging and diabetes.

Diabetic neuropathy--a continuing enigma

In this article we will review the clinical signs and symptoms of diabetic somatic polyneuropathy (DPN), its prevalence and clinical management. Staging and classification of DPN will be exemplified by various staging paradigms of varied sophistication. The results of therapeutic clinical trials will be summarized. The pathogenesis of diabetic neuropathy reviews an extremely complex issue that is still not fully understood. Various recent advances in the understanding of the disease will be discussed, particularly with respect to the differences between neuropathy in the two major types of diabetes. The neuropathology and natural history of diabetic neuropathy will be discussed pointing out the heterogeneities of the disease. Finally, the various prospective therapeutic avenues will be dealt with and discussed.

Cardiovascular disease in diabetes mellitus type 2: a potential role for novel cardiovascular risk factors

A major consequence of diabetes mellitus type 2 is the accelerated development of atherosclerosis. Assessment of conventional risk factors such as plasma lipids, lipoproteins and hypertension only partly account for the excessive risk of developing cardiovascular disease in this population. Increasing evidence has emerged suggesting that conditions associated with diabetes mellitus type 2, such as insulin resistance, hyperinsulinemia and hyperglycemia, may also play a significant role in regulating 'novel' cardiovascular risk factors. These factors and their potential roles in the development of atherosclerosis and cardiovascular events are discussed in this review.

Abnormalities of retinal metabolism in diabetes or experimental galactosemia VIII. Prevention by aminoguanidine

PURPOSE

Aminoguanidine has been found to inhibit the development of some retinal lesions in diabetic rats and diabetic dogs, thereby raising a possibility that the formation of glycation end products (AGEs) may be an essential step in the pathogenesis of the retinopathy. The purpose of this study is to investigate the effect of aminoguanidine administration on other metabolic abnormalities which might be involved in the development of retinopathy in two models of the retinopathy, alloxan diabetes and experimental galactosemia.

METHODS

Oxidative stress, nitric oxide (NO) and the activity of protein kinase C (PKC, total activity) were measured in the retina of the rats experimentally diabetic or galactosemic for 2 months. Effect of aminoguanidine administration on the inhibition of hyperglycemia-induced retinal dysmetabolism was investigated.

RESULTS

Two months of diabetes or experimental galactosemia in rats resulted in elevation of retinal oxidative stress (increase in thiobarbituric acid reactive substances, TBARS, and decrease in glutathione, GSH), NO, and PKC activity. Aminoguanidine supplementation (2.5 g aminoguanidine/kg rat diet) significantly inhibited each of these abnormalities in retinas of diabetic rats and galactosemic rats, and did so without lowering the blood hexose levels of these animals.

CONCLUSIONS

The ability of aminoguanidine to normalize the hyperglycemia-induced increases in retinal oxidative stress, NO and PKC in diabetic rats and galactose-fed rats suggests that these abnormalities may be inter-related in the retina, and that the biochemical mechanism by which aminoguanidine inhibits retinal microvascular disease in diabetes may be complex.

Maillard reactions by alpha-oxoaldehydes: detection of glyoxal-modified proteins

Proteins can be chemically modified by sugars by glycation, or the Maillard reaction. The Maillard reaction produces irreversible adducts on proteins that are collectively known as advanced glycation end products, or AGEs. Recent studies indicate that several alpha-dicarbonyl compounds, including glyoxal (GXL), are precursors of AGEs in vivo. We developed antibodies against a GXL-modified protein (GXL-AGE) and purified a mixture of GXL-AGE-specific antibodies by chromatography on GXL-modified bovine serum albumin (BSA-GXL) coupled to EAH-Sepharose. This preparation was then processed on a human serum albumin-carboxymethyllysine (HSA-CML)-NHS-Sepharose to remove CML-specific antibodies. We used the resulting purified antibody in a competitive ELISA to probe GXL-AGEs in vitro and in vivo. We found increasingly greater antibody binding with increasing concentrations of GXL-modified BSA, but the antibody failed to react with either free CML or protein-bound CML. Incubation experiments with BSA revealed that glyceraldehyde, ribose and threose could be precursors of GXL-AGEs as well. Experiments in which GXL was incubated with N-alpha-acetyl amino acids showed that the antibody reacts mostly with lysine modifications. The GXL-derived lysine-lysine crosslinking structure, GOLD was found to be one of the antigenic epitopes for the antibody. Analysis of human plasma proteins revealed significantly higher levels of GXL-AGE antigens in type II diabetic subjects compared with normal controls (P<0.0001). We also found GXL-AGEs in human lens proteins. Bovine aortic endothelial cells cultured for 7 days with 30 mM glucose did not accumulate intracellular GXL-AGEs. These studies underscore the importance of GXL for extracellular AGE formation (except in lens where it is likely to be formed intracellularly) and suggest that changes associated with age and diabetes might be prevented by alteration of GXL-AGE formation.

The missing link: a single unifying mechanism for diabetic complications

A causal relationship between chronic hyperglycemia and diabetic microvascular disease, long inferred from various animal and clinical studies, has now been definitely established by data from the Diabetes Control and Complications Trial (DCCT), a multicenter, randomized, prospective, controlled clinical study. A relationship between chronic hyperglycemia and diabetic macrovascular disease in patients with non-insulin-dependent diabetes mellitus (NIDDM) is also supported by the Kumamoto study. How does hyperglycemia induce the functional and morphologic changes that define diabetic complications? Vascular endothelial cells are a major target of hyperglycemic damage, but the mechanisms underlying this damage remain incompletely understood. Three seemingly independent biochemical pathways are involved in the pathogenesis: glucose-induced activation of protein kinase C (PKC) isoforms: increased formation of glucose-derived advanced glycation end products; and increased glucose flux through the aldose reductase pathway. The relevance of each of these three pathways is supported by animal studies in which pathway-specific inhibitors prevent various hyperglycemia-induced abnormalities. Hyperglycemia increases reactive oxygen species (ROS) production inside cultured bovine aortic endothelial cells. In this paper, we show that ROS may activate aldose reductase, induce diacylglycerol, activate PKC, induce advanced glycation end product formation, and activate the pleiotropic transcription factor nuclear factor-kappa B (NF-kappaB). These data demonstrate that a single unifying mechanism of induction, increased production of ROS, serves as a causal link between elevated glucose and each of the three major pathways responsible for diabetic damage.

Reactive oxygen species as glucose signaling molecules in mesangial cells cultured under high glucose

BACKGROUND

Oxidative stress is one of the important mediators of vascular complications in diabetes including nephropathy. High glucose (HG) generates reactive oxygen species (ROS) as a result of glucose auto-oxidation, metabolism, and formation of advanced glycosylation end products. The concept of ROS-induced tissue injury has recently been revised with the appreciation of new roles for ROS in signaling pathways and gene expression.

METHODS AND RESULTS

High glucose rapidly generated dichlorofluorescein-sensitive cytosolic ROS in rat and mouse mesangial cells. Neither L-glucose nor 3-O-methyl-D-glucose increased cytosolic ROS and cytochalasin B, an inhibitor of glucose transporter, effectively inhibited HG-induced ROS generation, suggesting that glucose uptake and subsequent metabolism are required in HG-induced cytosolic ROS generation. H2O2 up-regulated fibronectin mRNA expression and protein synthesis; this up-regulation was effectively inhibited by protein kinase C (PKC) inhibitor or by depletion of PKC. The HG-induced generation of ROS was, in turn, related to activation of PKC and transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) as well as to the up-regulation of transforming growth factor-beta1 (TGF-beta1), fibronectin mRNA expression and protein synthesis, because antioxidants effectively inhibited HG-induced PKC, NF-kappaB, AP-1 activation, and TGF-beta1 and fibronectin expression in mesangial cells cultured under HG.

CONCLUSIONS

Although signal transduction pathways linking HG, ROS, PKC, transcription factors, and extracellular matrix (ECM) protein synthesis in mesangial cells have not been fully elucidated, the current data provide evidence that ROS generated by glucose metabolism may act as integral signaling molecules under HG as in other membrane receptor signaling.

Expression of advanced glycation end products and their cellular receptor RAGE in diabetic nephropathy and nondiabetic renal disease

Advanced glycation end products (AGE) contribute to diabetic tissue injury by two major mechanisms, i.e., the alteration of extracellular matrix architecture through nonenzymatic glycation, with formation of protein crosslinks, and the modulation of cellular functions through interactions with specific cell surface receptors, the best characterized of which is the receptor for AGE (RAGE). Recent evidence suggests that the AGE-RAGE interaction may also be promoted by inflammatory processes and oxidative cellular injury. To characterize the distributions of AGE and RAGE in diabetic kidneys and to determine their specificity for diabetic nephropathy, an immunohistochemical analysis of renal biopsies from patients with diabetic nephropathy (n = 26), hypertensive nephrosclerosis (n = 7), idiopathic focal segmental glomerulosclerosis (n = 11), focal sclerosis secondary to obesity (n = 7), and lupus nephritis (n = 11) and from normal control subjects (n = 2) was performed, using affinity-purified antibodies raised to RAGE and two subclasses of AGE, i.e., N(epsilon)-(carboxymethyl)-lysine (CML) and pentosidine (PENT). AGE were detected equally in diffuse and nodular diabetic nephropathy. CML was the major AGE detected in diabetic mesangium (96%), glomerular basement membranes (GBM) (42%), tubular basement membranes (85%), and vessel walls (96%). In diabetic nephropathy, PENT was preferentially located in interstitial collagen (90%) and was less consistently observed in vessel walls (54%), mesangium (77%), GBM (4%), and tubular basement membranes (31%). RAGE was expressed on normal podocytes and was upregulated in diabetic nephropathy. The restriction of RAGE mRNA expression to glomeruli was confirmed by reverse transcription-PCR analysis of microdissected renal tissue compartments. The extent of mesangial and GBM immunoreactivity for CML, but not PENT, was correlated with the severity of diabetic glomerulosclerosis, as assessed pathologically. CML and PENT were also identified in areas of glomerulosclerosis and arteriosclerosis in idiopathic and secondary focal segmental glomerulosclerosis, hypertensive nephrosclerosis, and lupus nephritis. In active lupus nephritis, CML and PENT were detected in the proliferative glomerular tufts and crescents. In conclusion, CML is a major AGE in renal basement membranes in diabetic nephropathy, and its accumulation involves upregulation of RAGE on podocytes. AGE are also accumulated in acute inflammatory glomerulonephritis secondary to systemic lupus erythematosus, possibly via enzymatic oxidation of glomerular matrix proteins.

Atherosclerosis and diabetes: the RAGE connection

Diabetes mellitus begins as a disorder of glucose metabolism that progressively compromises the function of virtually every organ system as the secondary complications inexorably develop. The quality of life for patients with diabetes is diminished by the consequences of these complications. Accelerated and aggressive atherosclerosis is the greatest cause of morbidity and mortality with diabetes, emphasizing the importance of determining underlying mechanisms. This review highlights the role of the multiligand receptor for advanced glycation endproducts (RAGE) and two of its ligands, advanced glycation endproducts (AGEs) and S100/calgranulins, in the pathogenesis of atherosclerosis associated with diabetes. The results of the studies reviewed herein suggest that RAGE is a potential therapeutic target for macrovascular disease in diabetes.

The receptor for advanced glycation end products is induced by the glycation products themselves and tumor necrosis factor-alpha through nuclear factor-kappa B, and by 17beta-estradiol through Sp-1 in human vascular endothelial cells

The binding of advanced glycation end products (AGE) to the receptor for AGE (RAGE) is known to deteriorate various cell functions and is implicated in the pathogenesis of diabetic vascular complications. Here we show that AGE, tumor necrosis factor-alpha (TNF-alpha), and 17beta-estradiol (E(2)) up-regulated RAGE mRNA and protein levels in human microvascular endothelial cells and ECV304 cells, with the mRNA stability being essentially invariant. Transient transfection experiments with human RAGE promoter-luciferase chimeras revealed that the region from nucleotide number -751 to -629 and the region from -239 to -89 in the RAGE 5'-flanking sequence exhibited the AGE/TNF-alpha and E(2) responsiveness, respectively. Site-directed mutation of an nuclear factor-kappaB (NF-kappaB) site at -671 or of Sp-1 sites at -189 and -172 residing in those regions resulted in an abrogation of the AGE/TNF-alpha- or E(2)-mediated transcriptional activation. Electrophoretic mobility shift assays revealed that ECV304 cell nuclear extracts contained factors which retarded the NF-kappaB and Sp-1 elements, and that the DNA-protein complexes were supershifted by anti-p65/p50 NF-kappaB and anti-Sp-1/estrogen receptor alpha antibodies, respectively. These results suggest that AGE, TNF-alpha, and E(2) can activate the RAGE gene through NF-kappaB and Sp-1, causing enhanced AGE-RAGE interactions, which would lead to an exacerbation of diabetic microvasculopathy.

Protective effect of inducible type nitric oxide synthase against intracellular oxidative stress caused by advanced glycation end-products in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats

OBJECTIVE

A recent study demonstrated that free radicals were involved in the maintenance of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). However, the role of oxidative stress in hypertension and its related diseases in SHRSP remains unknown. On the other hand, advanced glycation end-products (AGEs) accumulate progressively in the vasculature with ageing, and have been identified to be as relevant mediators for various vascular complications. To elucidate whether nitric oxide (NO) produced by inducible type NO synthase (iNOS) in vascular smooth muscle cells (VSMC) taken from SHRSP and Wistar-Kyoto rats (WKY) attenuate AGEs-induced oxidative stress, we investigated the effect of NO donors and iNOS-induction in VSMC on intracellular oxidant level caused by AGEs.

METHODS

The cells preincubated with or without NO donor, S-nitroso-n-acetylpenicillamine (SNAP) or 3-morpholinosydnonimine (SIN-1), IL-1beta and/or N(G)-monomethyl-L-arginine monoacetate (L-NMMA), were treated with AGEs, and the intracellular oxidant levels, total glutathione (GSH) levels, and gamma-glutamylcysteine synthetase (GCS) mRNA were determined. We also determined the expression of an iNOS in VSMC from SHRSP and WKY.

RESULTS

The intracellular oxidant level of VSMC was induced by AGEs in a dose-dependent manner. NO donor dose-dependently reduced AGEs-stimulated intracellular oxidant level. Treatment with IL-1beta reduced the AGEs-stimulated intracellular oxidant level through increased NO production, whilst inhibition of NO production by L-NMMA reduced the inhibitory effect of IL-1beta. We also confirmed that NO production as well as the expression of iNOS mRNA and the protein itself were significantly decreased in response to IL-1beta in VSMC from SHRSP compared with WKY. We also confirmed that total GSH levels, decreased by AGEs, were restored by stimulation with IL-1beta. Increased GSH synthesis was due to enhanced expression of the rate-limiting enzyme for GSH synthesis, GCS. These results indicate that NO release, produced by iNOS in VSMC in response to cytokines, might play a protective role against AGEs-stimulated oxidative stress in VSMC. This protective effect of NO is decreased in SHRSP compared to WKY.

Relevance of oxidative and carbonyl stress to long-term uremic complications

Oxidative stress is a disturbance of balance between oxidants and antioxidant species. The existence of an increased oxidative stress in chronic renal failure is supported by evidence of increased lipid, carbohydrate, and protein oxidation products in plasma and cell membrane. Recent studies have implicated the oxidative stress in the nonenzymatic biochemistry leading to irreversible protein modifications. Reactive oxygen species may directly alter proteins with the eventual formation of oxidized amino acids. Alternatively, reactive carbonyl compounds formed by the oxidation of carbohydrates and lipids may indirectly lead to advanced glycation or lipoxidation of proteins. Chronic uremia is associated with increased modification of protein caused by reactive carbonyl compounds derived from both carbohydrates and lipids. Increased carbonyl modification of proteins subsequently results in the rise of plasma and tissue contents of advanced glycation end products and advanced lipoxidation end products, in which the deleterious biological effects have been revealed. This article focuses on the irreversible nonenzymatic modification of proteins, which might, at least in part, contribute to the development of complications associated with chronic renal failure and long-term dialysis, such as atherosclerosis and dialysis-related amyloidosis.

Cellular cofactors potentiating induction of stress and cytotoxicity by amyloid beta-peptide

Insights into factors underlying causes of familial Alzheimer's disease (AD), such as mutant forms of beta-amyloid precursor protein and presenilins, and those conferring increased risk of sporadic AD, such as isoforms of apolipoprotein E and polymorphisms of alpha2-macroglobulin, have been rapidly emerging. However, mechanisms through which amyloid beta-peptide (Abeta), the fibrillogenic peptide most closely associated with neurotoxicity in AD, exerts its effects on cellular targets have only been more generally outlined. Late in the course of AD, when Abeta fibrils are abundant, non-specific interactions of amyloid with cellular elements are likely to induce broad cytotoxicity. However, early in AD, when concentrations of Abeta are much lower and extracellular deposits are infrequent, mechanisms underlying cellular dysfunction have not been clearly defined. The key issue in elucidating the means through which Abeta perturbs cellular properties early in AD is the possibility that protective therapy at such times may prevent cytotoxicity at a point when damage is still reversible. This brief review focusses on two cellular cofactors for Abeta-induced cellular perturbation: the cell surface immunoglobulin superfamily molecule RAGE (receptor for advanced glycation endproducts) and ABAD (Abeta binding alcohol dehydrogenase). Although final proof for the involvement of these cofactors in cellular dysfunction in AD must await the results of further in vivo experiments, their increased expression in AD brain, as well as other evidence described below, suggests the possibility of specific pathways for Abeta-induced cellular perturbation which could provide future therapeutic targets.

Enzyme-like activity of glycated cross-linked proteins in free radical generation

The structure and property of cross-linked amino acids and proteins produced by a three- carbon alpha-dicarbonyl methylglyoxal in glycation reaction were investigated. Our results showed that these reactions generated yellow fluorescent products and several free radical species. From the reaction with alanine, three types of free radicals were identified by EPR spectroscopy: 1) the cross-linked radical cation, methylglyoxal diaklylimine cation radical; 2) the methylglyoxal radical anion as the counterion; 3) the superoxide radical anion produced only in the presence of oxygen. Glycation of bovine serum albumin by methylglyoxal also generated the protein-bound, cross-linked free radical, probably the cation radical of the cross-linked Schiff base as observed with alanine. The glycated protein reduced ferricytochrome c to ferrocytochrome c in the absence of oxygen or added metal ions. This reduction of cytochrome c was accompanied by a large increase in the amplitude of the electron paramagnetic resonance signal originated from the protein-bound free radical. In addition, the glycated protein catalyzed the oxidation of ascorbate in the presence of oxygen while the protein-free radical signal disappeared. These results indicate that glycation of protein generates active centers for catalyzing one-electron oxidation-reduction reactions. This active center, which exhibits enzyme-like character, was suggested to be the cross-linked Schiff base/the cross-linked Schiff base radical cation of the protein. It mimics the characteristics of metal-catalyzed oxidation system. These results together indicate that glycated proteins accumulated in vivo provide stable active-sites for catalyzing the formation of free radicals.

Molecular mechanism of diabetic nephropathy

Diabetic nephropathy is one of the main causes of renal end-stage disease. Morphologically, the development of diabetic nephropathy is characterized by progressive thickening of the glomerular basement membrane and by expansion of the mesangial matrix which correlates to glomerular filtration function. In vitro studies with cultured mesangial cells revealed that elevated glucose concentrations increase collagen synthesis similar to the in vivo situation. These studies showed that hyperglycemia may be toxic either by non-enzymatic reaction of glucose with proteins and subsequent formation of advanced glucosylation end products or by increased metabolism leading to increased oxidative stress and activation of protein kinase C resulting in increased production of cytokines. Particularly, de novo synthesis of transforming growth factor beta1 (TGF-beta1) is induced and TGF-beta1 appears also involved since blockage of this prosclerotic factor inhibits high glucose-induced collagen synthesis. Interestingly, it could be demonstrated that angiotensin II also stimulates TGF-beta1 production possibly via the same signal transduction pathway. Besides the classical clinical chemical parameters for evaluation of renal function, the measurement of urinary albumin excretion is now widely used for detection of developing diabetic nephropathy. Since diabetes causes glomerular and tubular changes, tubular marker proteins may be used to detect early renal damage. An increased urinary excretion of matrix proteins (e.g. collagen) and cytokines (e.g. TGF-beta1) was found in early diabetic nephropathy. However, the diagnostic value of these new parameters remains to be established.

Direct NAD(P)H hydrolysis into ADP-ribose(P) and nicotinamide induced by reactive oxygen species: a new mechanism of oxygen radical toxicity

The effect of different oxygen radical-generating systems on NAD(P)H was determined by incubating the reduced forms of the pyridine coenzymes with either Fe2+-H2O2 or Fe3+-ascorbate and by analyzing the reaction mixtures using a HPLC separation of adenine nucleotide derivatives. The effect of the azo-initiator 2,2'-azobis(2-methylpropionamidine)dihydrochloride was also tested. Results showed that, whilst all the three free radical-producing systems induced, with different extent, the oxidation of NAD(P)H to NAD(P)+, only Fe2+-H2O2 also caused the formation of equimolar amounts of ADP-ribose(P) and nicotinamide. Dose-dependent experiments, with increasing Fe2+ iron (concentration range 3-180 microM) or H2O2 (concentration range 50-1000 microM), were carried out at pH 6.5 in 50 mM ammonium acetate. NAD(P)+, ADP-ribose(P) and nicotinamide formation increased by increasing the amount of hydroxyl radicals produced in the medium. Under such incubation conditions NAD(P)+/ADP-ribose(P) ratio was about 4 at any Fe2+ or H2O2 concentration. By varying pH to 2.0, 3.0, 4.0, 4.5, 5.0, 5.5, 6.0, 7.0 and 7.4, NAD(P)+/ADP-ribose(P) ratio changed to 5.5, 3.2, 1.8, 1.6, 2.0, 2.5, 3.0, 5.4 and 6.5, respectively. Kinetic experiments indicated that 90-95% of all compounds were generated within 5s from the beginning of the Fenton reaction. Inhibition of ADP-ribose(P), nicotinamide and NAD(P)+ production of Fe2+-H2O2-treated NAD(P)H samples, was achieved by adding mannitol (10-50 mM) to the reaction mixture. Differently, selective and total inhibition of ADP-ribose(P) and nicotinamide formation was obtained by performing the Fenton reaction in an almost completely anhydrous medium, i.e. in HPLC-grade methanol. Experiments carried out in isolated postischemic rat hearts perfused with 50 mM mannitol, showed that, with respect to values of control hearts, this hydroxyl radical scavenger prevented reperfusion-associated pyridine coenzyme depletion and ADP-ribose formation. On the basis of these results, a possible mechanism of action of ADP-ribose(P) and nicotinamide generation through the interaction between NAD(P)H and hydroxyl radical (which does not involve the C-center where "conventional" oxidation occurs) is presented. The implication of this phenomenon in the pyridine coenzyme depletion observed in postischemic tissues is also discussed.

Blockade of RAGE-amphoterin signalling suppresses tumour growth and metastases

The receptor for advanced glycation end products (RAGE), a multi-ligand member of the immunoglobulin superfamily of cell surface molecules, interacts with distinct molecules implicated in homeostasis, development and inflammation, and certain diseases such as diabetes and Alzheimer's disease. Engagement of RAGE by a ligand triggers activation of key cell signalling pathways, such as p21ras, MAP kinases, NF-kappaB and cdc42/rac, thereby reprogramming cellular properties. RAGE is a central cell surface receptor for amphoterin, a polypeptide linked to outgrowth of cultured cortical neurons derived from developing brain. Indeed, the co-localization of RAGE and amphoterin at the leading edge of advancing neurites indicated their potential contribution to cellular migration, and in pathologies such as tumour invasion. Here we demonstrate that blockade of RAGE-amphoterin decreased growth and metastases of both implanted tumours and tumours developing spontaneously in susceptible mice. Inhibition of the RAGE-amphoterin interaction suppressed activation of p44/p42, p38 and SAP/JNK MAP kinases; molecular effector mechanisms importantly linked to tumour proliferation, invasion and expression of matrix metalloproteinases.

The indispensability of heme oxygenase-1 in protecting against acute heme protein-induced toxicity in vivo

Heme oxygenase (HO) is the rate limiting enzyme in the degradation of heme, and its isozyme, HO-1, may protect against tissue injury. One posited mechanism is the degradation of heme released from destabilized heme proteins. We demonstrate that HO-1 is a critical protectant against acute heme protein-induced toxicity in vivo. In the glycerol model of heme protein toxicity-one characterized by myolysis, hemolysis, and kidney damage-HO-1 is rapidly induced in the kidney of HO-1 +/+ mice as the latter sustain mild, reversible renal insufficiency without mortality. In stark contrast, after this insult, HO-1 -/- mice exhibit fulminant, irreversible renal failure and 100% mortality; HO-1 -/- mice do not express HO-1, and evince an eightfold increment in kidney heme content as compared to HO-1 +/+ mice. We also demonstrate directly the critical dependency on HO-1 in protecting against a specific heme protein, namely, hemoglobin: doses of hemoglobin which exert no nephrotoxicity or mortality in HO-1 +/+ mice, however, precipitate rapidly developing, acute renal failure and marked mortality in HO-1 -/- mice. We conclude that the induction of HO-1 is an indispensable response in protecting against acute heme protein toxicity in vivo.

Inflammation, insulin resistance, infection, diabetes, and atherosclerosis

OBJECTIVE

To review the relationship between poor control of blood glucose in patients with diabetes and potential for occurrence of the acute coronary syndrome.

METHODS

The role of advanced glycosylated end products in endothelial dysfunction is discussed, and the possible contributions of inflammation and infection in the rupture of atheromatous plaques are described.

RESULTS

Hyperglycemia predisposes to infection by decreasing the efficacy of leukocytes and allowing increased formation of advanced glycosylated end products. The associated endothelial permeability facilitates bacterial infiltration of atheromatous plaques. Reported associations between chronic infection and coronary artery disease have involved primarily Chlamydia pneumoniae. The insulin resistance syndrome is also characterized by compromised endothelial function, which may predispose patients to unstable plaques and cardiac events.

CONCLUSION

In patients with diabetes, poor glycemic control may lead to excessive advanced glycosylated end products, inflammation and infection of atheromatous plaques, and plaque rupture that can cause angina or myocardial infarction.

Oxidative stress occurs in absence of hyperglycaemia and inflammation in the onset of kidney lesions in normotensive obese rats

BACKGROUND

Several factors favour the development of kidney lesions. We examined the role of oxidative stress in the onset of renal alterations that occur in Zucker obese (ZO) fa/fa rats.

METHODS

Kidney structure, biological data, glycation parameters, advanced glycation end products (AGE), thiobarbituric acid-reactive substances (TBARS), circulating antibodies anti-malondialdehyde (MDA)-modified low-density lipoprotein (LDL), antioxidant defenses (Cu/Zn and Mn superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) activities, glutathione level), were determined in plasma and/or kidney of young and old ZO rats and lean (ZL) Fa/fa littermates.

RESULTS

Renal lesions and functional decline appeared at 3 months in hyperlipidaemic, hyperinsulinaemic, normotensive ZO rats, independently of any macrophage-ED(1)(+)-cell infiltration. At 6 months and thereafter, kidney lesions and functional impairment worsened while numerous ED(1)(+)-cells invaded the interstitium. At 3 and 9 months, TBARS level in the LDL/very low-density lipoprotein fraction and in the kidney was higher in ZO than in ZL rats. Anti-MDA-LDL antibodies were increased in ZO rats. At 3 months, renal activity of Cu/Zn SOD was higher, and activities of catalase and GPx lower in ZO than in ZL rats, leading to an accumulation of hydrogen peroxide (H(2)O(2)). At 9 months, a decrease in Cu/Zn SOD activity and an increase in glutathione level were observed. Blood glucose and glycated proteins, as well as AGE in kidney, remained similar in both ZL and ZO rats, whatever their age.

CONCLUSION

These data suggest that oxidative stress triggers, at an early age, the onset of kidney lesions and functional impairment in ZO rats, in absence of hyperglycaemia, hypertension and inflammation.

AGEs induce oxidative stress and activate protein kinase C-beta(II) in neonatal mesangial cells

Increased activation of specific protein kinase C (PKC) isoforms and increased nonenzymatic glycation of intracellular and extracellular proteins [the accumulation of advanced glycation end products (AGEs)] are major mechanistic pathways implicated in the pathogenesis of diabetic complications. Blocking PKC-beta(II) has been shown to decrease albuminuria in animal models of diabetes. To demonstrate a direct relationship between AGEs and the induction and translocation of PKC-beta(II), studies were carried out in rat neonatal mesangial cells, known to express PKC-beta(II) in association with rapid proliferation in post-natal development. Oxidative stress was studied by using the fluorescent probe dichlorfluorescein diacetate. Translocation of PKC-beta(II) was demonstrated by using immunofluorescence and Western blotting of fractionated mesangial cells. Induction of intracellular oxidative stress, increase in intracellular calcium, and cytosol to membrane PKC-beta(II) translocation (with no change in PKC-alpha) were demonstrated after exposure to AGE-rich proteins. These data support the hypothesis that AGEs cause mesangial oxidative stress and alterations in PKC-beta(II), changes that may ultimately contribute to phenotypic abnormalities associated with diabetic nephropathy.

Adaptive responses of the endothelium to stress

It is now established that endothelial cells acquire several functional properties in response to a diverse array of extracellular stimuli. This expression of an altered phenotype is referred to as endothelial cell activation, and it includes several activities that promote inflammation and coagulation. While it is recognized that endothelial cell activation has a principal role in host defense, recent studies also demonstrate that endothelial cells are capable of complex molecular responses that protect the endothelium against various forms of stress including heat shock, hypoxia, oxidative stress, shock, ischemia-reperfusion injury, toxins, wounds, and mechanical stress. In this review, we examine endothelial cell genotypic and phenotypic responses to stress. Also, we highlight important cellular stress responses that, although not yet demonstrated directly in endothelial cells, likely exist as part of the repertoire of stress responses in endothelium. A detailed understanding of the molecular mechanisms mediating the adaptive responses of endothelial cells to stress should facilitate the development of novel therapeutics to aid in the management of diverse surgical diseases and their complications.

Negative consequences of glycation

The Diabetes Control and Complications Trial (DCCT) established unequivocally that the effects of inadequate insulin action (as monitored by the level of hyperglycemia) are associated with the incidence and progression of diabetic retinopathy, nephropathy, and neuropathy. How does hyperglycemia induce the functional and morphologic changes that characterize diabetic complications? Increasing evidence points to a major role for sugar-derived advanced glycation end products (AGEs), which form inside and outside cells as a function of glucose concentration. Recent work in this area supports a central role for reactive oxygen species (ROS) in both the formation of AGEs, and in AGE-induced pathologic alterations in gene expression. Inhibition of ROS may also be centrally important in the action of drugs that prevent complications in diabetic animal models.

What is oxidative stress?

Oxidative stress, defined as a disturbance in the balance between the production of reactive oxygen species (free radicals) and antioxidant defenses, is discussed in relation to its possible role in the production of tissue damage in diabetes mellitus. Important free radicals are described and biological sources of origin discussed, together with the major antioxidant defense mechanisms. Examples of the possible consequences of free radical damage are provided with special emphasis on lipid peroxidation. Finally, the question of whether oxidative stress is increased in diabetes mellitus is discussed.

Time-course changes in plasma endothelin-1 and its effects on the mesenteric arterial bed in streptozotocin-induced diabetic rats

AIM

To examine the mechanisms underlying the elevated plasma endothelin-1 (ET-1) in diabetes and its vascular effects.

RESULTS

Relationships between the plasma ET-1 level and the levels of other plasma constituents (glucose, cholesterol, and triglyceride) were found in 10-week streptozotocin (STZ)-induced diabetic rats. In contrast, at 1 week after the STZ injection only plasma ET-1 and glucose levels were elevated, suggesting that the hyperglycaemia might trigger the excess production of ET-1. Incubation with high glucose promoted the release of ET-1 from the isolated mesenteric arterial bed. In STZ-induced diabetic rats, the maximum contractile response of the mesenteric arterial bed to ET-1 was significantly reduced, and the vasoconstriction and vasodilation induced by the ET(B)-receptor agonist IRL-1620 in this bed were significantly impaired. The vascular responses induced by these ET receptor agonists were restored to normal by chronic treatment of diabetic rats with insulin for 7 or 4 weeks.

CONCLUSIONS

These results suggest: (1) that the marked increase in plasma glucose in STZ-induced diabetic rats elevates the plasma ET-1; and (2) that the decreased contractile and vasodilator responses of the mesenteric arterial bed to ET-1 receptor agonists may be due to desensitization of not only ET(A), but also ET(B) receptors, an effect secondary to the elevation of plasma ET-1.

Interaction between osmotic and oxidative stress in diabetic precataractous lens: studies with a sorbitol dehydrogenase inhibitor

Both sorbitol accumulation-linked osmotic stress and "pseudohypoxia" [increase in NADH/NAD+, similar to that in hypoxic tissues, and attributed to increased sorbitol dehydrogenase (1-iditol:NAD+ 5-oxidoreductase; EC 1.1.1.14; SDH) activity] have been invoked among the mechanisms underlying oxidative injury in target tissues for diabetic complications. We used the specific SDH inhibitor SDI-157 [2-methyl-4(4-N,N-dimethylaminosulfonyl-1-piperazino)pyrimid ine] to evaluate the role of osmotic stress versus "pseudohypoxia" in oxidative stress occurring in diabetic precataractous lens. Control and diabetic rats were treated with or without SDI-157 (100 mg/kg/day for 3 weeks). Lens malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HA), MDA, GSH, and ascorbate levels, as well as the GSSG/GSH ratios, were similar in SDI-treated and untreated control rats, thus indicating that SDI-157 was not a prooxidant. Intralenticular osmotic stress, manifested by sorbitol levels, was more severe in SDI-treated diabetic rats (38.2+/-6.8 vs 21.2+/-3.5 micromol/g in untreated diabetic and 0.758+/-0.222 micromol/g in control rats, P<0.01 for both), while the decrease in the free cytosolic NAD+/NADH ratio was partially prevented (120+/-16 vs 88+/-11 in untreated diabetic rats and 143+/-13 in controls, P<0.01 for both). GSH and ascorbate levels were decreased, while MDA plus 4-HA and MDA levels were increased in diabetic rats versus controls; both antioxidant depletion and lipid aldehyde accumulation were exacerbated by SDI treatment. Superoxide dismutase (superoxide:superoxide oxidoreductase; EC 1.15.1.1), GSSG reductase (NAD[P]H:oxidized-glutathione oxidoreductase; EC 1.6.4.2), GSH transferase (glutathione S-transferase; EC 2.5.1.18), GSH peroxidase (glutathione:hydrogen-peroxide oxidoreductase; EC 1.11.1.9), and cytoplasmic NADH oxidase activities were increased in diabetic rats versus controls, and all the enzymes but GSH peroxidase were up-regulated further by SDI. In conclusion, sorbitol accumulation and osmotic stress generated oxidative stress in diabetic lens, whereas the contribution of "pseudohypoxia" was minor. SDIs provide a valuable tool for exploring mechanisms of oxidative injury in sites of diabetic complications.

Tyrosine phosphorylation of caveolin-1 in the endothelium

Caveolin-1, a scaffolding protein of caveolae, is known to be tyrosine-phosphorylated by Src kinases. Recently we generated a specific antibody to caveolin-1 phosphorylated at tyrosine-14 (PY14) (R. Nomura and T. Fujimoto, 1999, Mol. Biol. Cell 10, 975-986). In the present study, by applying PY14 to sections of normal rat tissues, we found that tyrosine phosphorylation of caveolin-1 occurred in limited locations, including the endothelium of the continuous capillaries and small venules. Cultured endothelial cells were not labeled by PY14 under a standard culture condition, but became positively labeled when exposed to oxidative stresses and/or tyrosine phosphatase inhibitors. The reaction was prohibited by pretreating the cells with herbimycin A or genistein. Vasoactive reagents or physical stimuli did not cause the phosphorylation. Concomitant with the tyrosine phosphorylation, the number of invaginated caveolae decreased drastically, and vesicles labeled intensely for caveolin-1 appeared in the cytoplasm; the average diameter of the vesicles was larger than that of caveolae. The result implies that tyrosine phosphorylation of caveolin-1 occurs at tyrosine-14 in the normal rat endothelium in vivo and may induce caveolar vesiculation and/or fusion.

Modification of beta 2-microglobulin with D-glucose or 3-deoxyglucosone inhibits A beta 2M amyloid fibril extension in vitro

beta 2-microglobulin (beta 2M) is a major constituent of amyloid fibrils (fA beta 2M) deposited in patients with A beta 2M amyloidosis. Recently, advanced glycation end products (AGE) of beta 2M and fA beta 2M have been suggested to play an important role in the pathogenesis of A beta 2M amyloidosis. We first characterized the states of AGE modification of fA beta 2M. Western blot analysis with a monoclonal anti-AGE antibody showed that purified fA beta 2M was naturally modified with AGE. Immunohistochemical studies of amyloid-deposited tissue have revealed a patchy distribution of the AGE-modified area in the amyloid deposits. Then we modified beta 2-m either with D-glucose or with 3-deoxyglucosone (3-DG) and investigated the effect of these modification on fA beta 2M extension in vitro, using the recently established first-order kinetic model of fA beta 2M extension in vitro. Western blot analysis and enzyme linked immunosorbent assay with a monoclonal anti-AGE antibody showed that these sugar-modified beta 2M contained AGE. During the incubation of fA beta 2M with native beta 2-m at 37 degrees C, the fluorescence of thioflavin T increased without a lag phase and proceeded to equilibrium. On the contrary, only a slight increase in fluorescence was observed during the incubation of fA beta 2M with sugar-modified beta 2M. Moreover, sugar-modified beta 2M exhibited a dose-dependent inhibitory effect on the extension reaction of fA beta 2M with native beta 2M. These results may suggest that in some in vivo situations, the modification of beta 2-m with AGE could play an inhibitory role for the formation of fA beta 2M.

Carnosine protects against excitotoxic cell death independently of effects on reactive oxygen species

The role of carnosine, N-acetylcarnosine and homocarnosine as scavengers of reactive oxygen species and protectors against neuronal cell death secondary to excitotoxic concentrations of kainate and N-methyl-D-aspartate was studied using acutely dissociated cerebellar granule cell neurons and flow cytometry. We find that carnosine, N-acetylcarnosine and homocarnosine at physiological concentrations are all potent in suppressing fluorescence of 2',7'-dichlorofluorescein, which reacts with intracellularly generated reactive oxygen species. However, only carnosine in the same concentration range was effective in preventing apoptotic neuronal cell death, studied using a combination of the DNA binding dye, propidium iodide, and a fluorescent derivative of the phosphatidylserine-binding dye, Annexin-V. Our results indicate that carnosine and related compounds are effective scavengers of reactive oxygen species generated by activation of ionotropic glutamate receptors, but that this action does not prevent excitotoxic cell death. Some other process which is sensitive to carnosine but not the related compounds is a critical factor in cell death. These observations indicate that at least in this system reactive oxygen species generation is not a major contributor to excitotoxic neuronal cell death.

Management of oxidative stress in the CNS: the many roles of glutathione

An outline is given of mechanisms that generate oxidative stress and inflammation. Considered are the metabolic mechanisms that give rise to peroxides, the source of strong oxidants; the production of dicarbonyls that interact with macromolecules to form advanced glycation endproducts; and the role that activation of the transcription factor NF(Kappa)B has in the expression of pro-inflammatory genes. Management of oxidative stress is considered by outlining the central role of reduced glutathione (GSH) in peroxide scavenging, dicarbonyl scavenging and activation of NF(Kappa)B. Cellular GSH levels are dictated by the balance between consumption, oxidation of GSH, reduction of oxidized-glutathione, and synthesis. The rate-limiting enzyme in GSH synthesis is L-gamma-glutamyl-L-cysteine synthase, a phase II enzyme. Phase II enzyme inducers are found in many fruits and vegetables. It is suggested that dietary phase II enzyme inducers be investigated for their potential for preventing or retarding the development of degenerative diseases that have an underlying oxidative stress and inflammatory component.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

Activators and target genes of Rel/NF-kappaB transcription factors

The vertebrate transcription factor NF-kappaB is induced by over 150 different stimuli. Active NF-kappaB, in turn, participates in the control of transcription of over 150 target genes. Because a large variety of bacteria and viruses activate NF-kappaB and because the transcription factor regulates the expression of inflammatory cytokines, chemokines, immunoreceptors, and cell adhesion molecules, NF-kappaB has often been termed a 'central mediator of the human immune response'. This article contains a complete listing of all NF-kappaB inducers and target genes described to date. The collected data argue that NF-kappaB functions more generally as a central regulator of stress responses. In addition, NF-kappaB activation blocks apoptosis in several cell types. Coupling stress responsiveness and anti-apoptotic pathways through the use of a common transcription factor may result in increased cell survival following stress insults.

Antioxidant enzymes and human diseases

OBJECTIVES

To describe the importance of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase working together in human cells against toxic reactive oxygen species, their relationship with several pathophysiologic processes and their possible therapeutic implications.

CONCLUSIONS

Reactive oxygen species (ROS) are involved in the cell growth, differentiation, progression, and death. Low concentrations of ROS may be beneficial or even indispensable in processes such as intracellular signaling and defense against micro-organisms. Nevertheless, higher amounts of ROS play a role in the aging process as well as in a number of human disease states, including cancer, ischemia, and failures in immunity and endocrine functions. As a safeguard against the accumulation of ROS, several nonenzymatic and enzymatic antioxidant activities exist. Therefore, when oxidative stress arises as a consequence of a pathologic event, a defense system promotes the regulation and expression of these enzymes.

A receptor for advanced glycosylation endproducts (AGEs) is colocalized with neurofilament-bound AGEs and SOD1 in motoneurons of ALS: immunohistochemical study

Neurofilament (NF)-bound AGEs colocalize immunochemically with SOD1 in the motoneurons of patients with ALS. Among three types of AGE receptors reported in the human brain, AGE-R1 (oligosaccharyltransferase family) and AGE-R2 (substrate of protein kinase C) have been found in neurons, while AGE-R3 is restricted to glia. The present study investigates which of these receptors may be responsible for binding AGEs in the NF conglomerates of motoneurons. Immunostaining of paraffin sections from eight ALS patients (five sporadic and three familial) and three control cases was performed with antibodies directed against R1 and R2, in parallel with those against AGEs and SOD1. The sites of AGE-R1 immunoreactivity (IR) in motoneurons were in conformity to those of NF-associated AGE and SOD1 IRs. By contrast, the IR of R2 was negative in NF conglomerates. Negative R2 IR for NF conglomerates was outlined by surrounding coarse R2 immunopositive granules in the perikaryon. No IR for R1 or R2 was found in hyaline or Bunina inclusions. There was no extraneuronal expression of IR for AGE-R1 or AGEs in microglia or astroglia around the NF accumulation. The colocalization of AGE, AGE-R1, and SOD1 at NF conglomerates in motoneurons supports the notion that AGE-mediated oxidative stress and protein aggregation may be implicated in NF conglomeration and ALS pathogenesis.

N(epsilon)-(carboxymethyl)lysine adducts of proteins are ligands for receptor for advanced glycation end products that activate cell signaling pathways and modulate gene expression

Recent studies suggested that interruption of the interaction of advanced glycation end products (AGEs), with the signal-transducing receptor receptor for AGE (RAGE), by administration of the soluble, extracellular ligand-binding domain of RAGE, reversed vascular hyperpermeability and suppressed accelerated atherosclerosis in diabetic rodents. Since the precise molecular target of soluble RAGE in those settings was not elucidated, we tested the hypothesis that predominant specific AGEs within the tissues in disorders such as diabetes and renal failure, N(epsilon)-(carboxymethyl)lysine (CML) adducts, are ligands of RAGE. We demonstrate here that physiologically relevant CML modifications of proteins engage cellular RAGE, thereby activating key cell signaling pathways such as NF-kappaB and modulating gene expression. Thus, CML-RAGE interaction triggers processes intimately linked to accelerated vascular and inflammatory complications that typify disorders in which inflammation is an established component.