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

Estrogen has opposing effects on vascular reactivity in obese, insulin-resistant male Zucker rats

We hypothesized that estradiol treatment would improve vascular dysfunction commonly associated with obesity, hyperlipidemia, and insulin resistance. A sham operation or 17beta-estradiol pellet implantation was performed in male lean and obese Zucker rats. Maximal vasoconstriction (VC) to phenylephrine (PE) and potassium chloride was exaggerated in control obese rats compared with lean rats, but estradiol significantly attenuated VC in the obese rats. Estradiol reduced the PE EC50 in all groups. This effect was cyclooxygenase independent, because preincubation with indomethacin reduced VC response to PE similarly in a subset of control and estrogen-treated lean rats. Endothelium-independent vasodilation (VD) to sodium nitroprusside was similar among groups, but endothelium-dependent VD to ACh was significantly impaired in obese compared with lean rats. Estradiol improved VD in lean and obese rats by decreasing EC50 but impaired function by decreasing maximal VD. The shift in EC50 corresponded to an upregulation in nitric oxide synthase III protein expression in the aorta of the estrogen-treated obese rats. In summary, estrogen treatment improves vascular function in male insulin-resistant, obese rats, partially via an upregulation of nitric oxide synthase III protein expression. These effects are counteracted by adverse factors, such as hyperlipidemia and, potentially, a release of an endothelium-derived contractile agent.

Receptor for advanced glycation endproducts (RAGE) and vascular inflammation: insights into the pathogenesis of macrovascular complications in diabetes

The incidence and severity of atherosclerosis is increased in patients with diabetes. Indeed, accelerated macrovascular disease in diabetic patients has emerged as a leading cause of morbidity and mortality in the United States and worldwide. Multiple investigations have suggested that there are numerous potential contributory factors that underlie these observations. Our laboratory has focused on the contribution of receptor for advanced glycation endproducts (RAGE) and its proinflammatory ligands, advanced glycation endproducts (AGEs) and S100/calgranulins in vascular perturbation, manifested as enhanced atherogenesis or accelerated restenosis after angioplasty. In rodent models of diabetic complications, blockade of RAGE suppressed vascular hyperpermeability, accelerated atherosclerotic lesion area and complexity in diabetic apolipoprotein E-deficient mice, and prevented exaggerated neointimal formation in hyperglycemic fatty Zucker rats subjected to injury of the carotid artery. In this review, we summarize these findings and provide an overview of distinct mechanisms that contribute to the development of accelerated diabetic macrovascular disease. Insights into therapeutic strategies to prevent or interrupt these processes are presented.

Receptor for advanced glycation end products on human synovial fibroblasts: role in the pathogenesis of dialysis-related amyloidosis

An important component of amyloid fibrils in dialysis-related amyloidosis (DRA) is beta(2)-microglobulin (beta(2)m) modified with advanced glycation end products (AGE). The amyloid deposits are located principally in joint structures, with adjacent chronic inflammatory reaction characterized by monocyte infiltration. This study examined the interaction of AGE-beta(2)m with human synovial fibroblasts and investigated the proinflammatory effects of that interaction. It was demonstrated that human synovial fibroblasts constitutively expressed the receptor for AGE (RAGE). RAGE expression was detected mainly in synovial intima and was upregulated in DRA synovium. (125)I-AGE-beta(2)m bound to immobilized human synovial fibroblasts in a specific, dose-dependent manner (K(d) of approximately 138.0 nM), and binding was inhibited by anti-RAGE IgG. Incubation of human synovial fibroblasts with AGE-beta(2)m induced degradation of this AGE-modified protein, as well as increased monocyte chemoattractant protein-1 (MCP-1) mRNA and protein expression. The amount of MCP-1 produced by AGE-beta(2)m-stimulated human synovial fibroblasts was sufficient to induce the chemotaxis of monocytes. MCP-1 synthesis resulted from engagement of RAGE, because the increase in MCP-1 synthesis was attenuated by preincubation of human synovial fibroblasts with anti-RAGE IgG. These data provide evidence of RAGE-mediated perturbation of human synoviocytes, which may be involved in the pathogenesis of inflammatory processes associated with DRA.

Reactive oxygen species accelerate production of vascular endothelial growth factor by advanced glycation end products in RAW264.7 mouse macrophages

Advanced glycation end products (AGEs) are believed to play an important role in the development of angiopathy in diabetes mellitus. Previous reports suggested a correlation between accumulation of AGEs and production of vascular endothelial growth factor (VEGF) in human diabetic retina. However, the mechanisms involved were not revealed. In this study, we investigated the transcriptional regulation of the expression of vascular endothelial growth factor (VEGF) by AGEs, and possible involvement of reactive oxygen species (ROS) in the induction. We employed an AGE of bovine serum albumin (BSA) prepared by an incubation of BSA with D-glucose for 40 weeks and N(epsilon)-(carboxymethyl)lysine (CML), a major AGE. The expression of VEGF was induced by CML-BSA in RAW264.7 mouse macrophage-like cells. CML-BSA stimulated the DNA-binding activity of activator protein-1 (AP-1). Promoter assay showed that the induction of VEGF was dependent on AP-1. The activity of Ras/Raf-1/MEK/ERK1/2 was involved in the CML-BSA-stimulated signaling pathways to activate the AP-1 transcription with a peak at 1 h. AGE-BSA also induced VEGF mediated by AP-1, however, there was a difference of effect between AGE-BSA and CML-BSA in the activation of AP-1. AGE-BSA-stimulated AP-1 activity showed a peak at 5 h, which paralleled the formation of ROS. Reduction of AGE-BSA with NaBH(4) or addition of vitamin E attenuated the AGE-BSA-stimulated signaling pathways leading to the same pattern as for CML-BSA-stimulated signals. These results suggest an important role for AGEs in stimulation of the development of angiogenesis observed in diabetic complications, and that ROS accelerates the AGE-stimulated VEGF expression.

Cellular oxidant stress and advanced glycation endproducts of albumin: caveats of the dichlorofluorescein assay

In order to understand the mechanism by which advanced glycation endproducts (AGEs) elicit oxidative stress, macrophage-like RAW264.7 cells were exposed to various AGE-albumins, and oxidant stress was estimated from the fluorescence of oxidized dichlorofluorescein using the microtiter plate assay. Strongest fluorescence was observed with methylglyoxal modified albumin (MGO-BSA) compared with native albumin. Similar effects that were prevented by arginine coincubation were seen with phenylglyoxal-BSA. MGO-BSA had increased affinity for Cu(2+) and Ca(2+), but was conformationally similar to native albumin. Surprisingly, the mere addition of unmodified albumin to cells suppressed the fluorescence of oxidized DCF. While, several site-directed mutants of human serum albumin (HSA), including C34S and recombinant domains II and III retained fluorescence suppressing activity, proteolytic digests, recombinant domain I, and several nonalbumin proteins failed to suppress. Kinetic and ANS binding studies suggested albumin quenches DCF fluorescence by binding to hydrophobic pockets in domains II and III and that MGO-BSA is less hydrophobic than BSA. Finally, BSA also prevented H(2)O(2) catalyzed DCF fluorescence more potently than MGO-BSA. These studies reveal important caveats of the widely used dichlorofluorescein assay and suggest methods other than the microtiter plate assay are needed to accurately assess cellular oxidant stress in presence of native or modified albumin.

Coronary microvascular adaptation to myocardial metabolic demand can be restored by inhibition of iron-catalyzed formation of oxygen free radicals in type 2 diabetic patients

Dilation of coronary vessels is impaired in diabetic patients when myocardial metabolic demand is increased. Deferoxamine (DFX) restores a normal dilation of epicardial coronary arteries. To assess the effects of DFX on metabolic coronary microvascular dilation in type 2 diabetic patients, coronary blood flow was measured using intracoronary Doppler and quantitative angiography in 17 type 2 diabetic patients with normal coronary arteries and without any other coronary risk factors. Measurements were made at baseline and during a cold pressor test (CPT), before and after intravenous administration of DFX. With a similar rate-pressure product (RPP) increase during CPT before and after DFX (+21.1 +/- 8.7 vs. +20.5 +/- 8.9%, respectively), coronary blood flow increase was significantly enhanced after DFX (+31.8 +/- 16.7 vs. +6.3 +/- 12.9% before DFX, P < 0.001). Moreover, coronary resistance increased during CPT before DFX and decreased after DFX (+14.8 +/- 21.9 vs. -7.9 +/- 10.9%, respectively, P < 0.001). Lastly, the negative relationship between coronary blood flow and RPP before DFX (R = 0.546, P < 0.05) was changed in a positive relationship after DFX (R = 0.518, P < 0.05). In conclusion, in type 2 diabetic patients, inhibition of iron-catalyzed oxidative reactions by DFX restored dilation of the coronary microcirculation and a normal matching between myocardial metabolic demand and coronary blood flow.

Toward better dialysis compatibility: advances in the biochemistry and pathophysiology of the peritoneal membranes

Peritoneal dialysis (PD) has modified our concept of the peritoneal membrane, which is now a topic of active research. Peritoneal solute transport progressively increases with time on PD, enhances the dissipation of the osmotic gradient and, eventually, reduces ultrafiltration capacity. The causes of peritoneal membrane failure remain elusive. Recurrent episodes of peritonitis are not a prerequisite for the development of ultrafiltration failure. Functionally, the changes of the failing peritoneal membrane are best described as an increased functional area of exchange for small solutes between blood and dialysate. Histologically, these events are associated with vascular proliferation and structural changes of pre-existing vessels. Gathered evidence, including information on the composition of peritoneal cavity fluids and its dependence on the uremic environment, have cast a new light on the molecular mechanisms of decline in peritoneal membrane function. Chronic uremia per se modifies the peritoneal membrane and increases the functional area of exchange for small solutes. Biochemical alterations in the peritoneum inherent to uremia might be, at least in part, accounted for by severe reactive carbonyl compounds overload originating both from uremic circulation and PD fluid ("peritoneal carbonyl stress"). The molecular events associated with long-term PD are similar but more severe than those present in chronic uremia without PD, including modifications of nitric oxide synthase (NOS) and angiogenic growth factors expression, and advanced glycation and lipoxidation of the peritoneal proteins. This review focuses on reactive carbonyls and their association with a number of molecular changes observed in peritoneal tissues. This hypothetical approach will require further testing. Nevertheless, the insights gained on the peritoneal membrane offer a new paradigm to assess the effect of uremic toxins on serosal membranes. Furthermore, the progresses made in the dissection of the molecular events leading to peritoneal membrane failure open new avenues to develop safe, more biocompatible peritoneal dialysis technologies.

Advanced glycation end products-induced apoptosis and overexpression of vascular endothelial growth factor in bovine retinal pericytes

The influence of advanced glycation end products (AGEs) on apoptotic cell death and vascular endothelial growth factor (VEGF) gene expression in cultured bovine retinal pericytes was investigated. When pericytes were incubated with three immunochemically distinct AGEs, which were prepared in vitro by incubating bovine serum albumin with glucose, glyceraldehyde, or glycolaldehyde, apoptotic cell death and DNA ladder formation were significantly induced. The cytopathic effects of glyceraldehyde- or glycolaldehyde-derived AGEs were significantly enhanced in AGE receptor-transfected pericytes. Furthermore, all of these AGEs were found to upregulate the secretory forms of VEGF mRNA levels in retinal pericytes. These results suggest that AGEs disturbed retinal microvascular homeostasis by inducing pericyte apoptosis and VEGF overproduction and thus were involved in the pathogenesis of early phase diabetic retinopathy.

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

An aldose reductase inhibitor reverses early diabetes-induced changes in peripheral nerve function, metabolism, and antioxidative defense

Aldose reductase inhibitors (ARIs) prevent peripheral nerve dysfunction and morphological abnormalities in diabetic animal models. However, some experimental intervention studies and clinical trials of ARIs on diabetic neuropathy appeared disappointing because of either 1) their inadequate design and, in particular, insufficient correction of the sorbitol pathway activity or 2) the inability to reverse established functional and metabolic deficits of diabetic neuropathy by AR inhibition in general. We evaluated whether diabetes-induced changes in nerve function, metabolism, and antioxidative defense are corrected by the dose of ARI (sorbinil, 65 mg/kg/d in the diet), resulting in complete inhibition of increased sorbitol pathway activity. The groups included control rats and streptozotocin-diabetic rats treated with/without ARI for 2 weeks after 4 weeks of untreated diabetes. ARI treatment corrected diabetes-induced nerve functional changes; that is, decrease in endoneurial nutritive blood flow, motor and sensory nerve conduction velocities, and metabolic abnormalities (i.e., mitochondrial and cytosolic NAD+/NADH redox imbalances and energy deficiency). ARI restored nerve concentrations of two major non-enzymatic antioxidants, reduced glutathione (GSH) and ascorbate, and completely arrested diabetes-induced lipid peroxidation. In conclusion, treatment with adequate doses of ARIs (that is, doses that completely inhibit increased sorbitol pathway activity) is an effective approach for reversal of, at least, early diabetic neuropathy.

AGEs bind to mesothelial cells via RAGE and stimulate VCAM-1 expression

BACKGROUND

Excess advanced glycation end-products (AGEs) are formed during renal failure, and AGE formation also may be connected with the high glucose concentration of peritoneal dialysis (PD) fluids. To determine the effect of human peritoneal mesothelial cell (HPMC) exposure to glycated proteins, we studied the HPMC receptor of AGE expression (RAGE), and analyzed the results of AGE-RAGE interaction on adhesion molecule expression and leukocyte binding.

METHODS

RAGE was detected by FACS analysis, and RAGE mRNA by reverse transcription-polymerase chain reaction (RT-PCR). Vascular and intercellular cell adhesion molecule (VCAM-1 and ICAM-1) expression was measured by a known radiometric technique under basal conditions, after the addition of an AGE-specific compound, Nepsilon-carboxylmethyllysine (CML-albumin). Leukocyte adhesion on HPMC was analyzed by videomicroscopy after HPMC stimulation.

RESULTS

RAGE protein was detected on HPMC, and RAGE mRNA was evidenced by RT-PCR. VCAM-1 expression was stimulated by CML-albumin (P < 0.01), while ICAM-1 was unchanged. By blocking the AGE-RAGE interaction, anti-RAGE antibodies or recombinant RAGE inhibited the increase in VCAM-1 expression. CML-albumin stimulation potentiated leukocyte adhesion to HPMC (P < 0.001). This effect was prevented by the incubation of leukocytes with recombinant VCAM-1 (P < 0.001).

CONCLUSIONS

AGE binding to RAGE stimulated mesothelial cell activity, and resulted in the overexpression of VCAM-1, a structure for leukocyte adhesion. The AGE-RAGE interaction resulted in HPMC activation, which may promote local inflammation, and thus is implicated in the peritoneal injury found in long-term PD patients.

Mechanisms in the development of type 2 diabetes mellitus

The leading cause of death among patients with type 2 diabetes mellitus (DM) is cardiovascular disease, with 75% of these deaths attributed to coronary heart disease. Over the previous two decades the pathophysiological basis of type 2 DM has been extensively investigated. Although many of the underlying molecular mechanisms involved in the development of this disorder remain to be explained, it is clear that type 2 DM is a complex medical disorder characterized by insulin resistance and defects in insulin secretion. The process through which the metabolic derangements of type 2 DM accelerate the development of cardiovascular disease in type 2 DM has yet to be determined and remains an area of intense investigation, focusing on hyperglycemia and insulin resistance as major underlying contributors. This article explores current information related to the pathophysiology of type 2 DM alone and its relationship to the development to cardiovascular disease.

Oxidative stress and cardiovascular disease in type 2 diabetes: the role of antioxidants and pro-oxidants

Oxidative stress occurs when there is an imbalance between free radical production and antioxidant capacity. This may be due to increased free radical formation in the body and/or loss of normal antioxidant defenses. Oxidative stress has been associated with the development of cardiovascular disease. The role of antioxidants in the primary and secondary prevention of coronary heart disease is currently under study. Although epidemiologic evidence indicates that antioxidants may decrease cardiovascular risk, clinical trial data are not conclusive. Information regarding the use and benefits of antioxidants in persons with diabetes is limited. Persons with diabetes may be more prone to oxidative stress because hyperglycemia depletes natural antioxidants and facilitates the production of free radicals. In addition, other factors such as homocysteine, insulin resistance, and aging may be contributory. This article highlights landmark clinical trials that have examined the cardioprotective effect of antioxidants. Because these trials have not been designed to study persons with diabetes, and clinical trial data for this group are not available, correlational studies are also presented. Finally, the concept of oxidative stress, the antioxidant and pro-oxidant factors that may contribute to oxidative stress, and the consequences of oxidative stress in persons with type 2 diabetes are presented. Key words: antioxidants, clinical trials,

Advanced glycation end products cause epithelial-myofibroblast transdifferentiation via the receptor for advanced glycation end products (RAGE)

Tubulointerstitial disease, a prominent phenomenon in diabetic nephropathy, correlates with decline in renal function. The underlying pathogenic link between chronic hyperglycemia and the development of tubulointerstitial injury has not been fully elucidated, but myofibroblast formation represents a key step in the development of tubulointerstitial fibrosis. RAGE, the receptor for advanced glycation end products (AGEs), induces the expression of TGF-beta and other cytokines that are proposed to mediate the transdifferentiation of epithelial cells to form myofibroblasts. Here we report specific binding of (125)I-AGE-BSA to cell membranes prepared from a rat proximal tubule cell line and show that the binding site was RAGE. AGE exposure induced dose-dependent epithelial-myofibroblast transdifferentiation determined by morphological changes, de novo alpha smooth-muscle actin expression, and loss of epithelial E-cadherin staining. These effects could be blocked with neutralizing Ab's to RAGE or to TGF-beta. Transdifferentiation was also apparent in the proximal tubules of diabetic rats and in a renal biopsy from a patient with type 1 diabetes. The AGE cross-link breaker, phenyl-4,5-dimethylthiazolium bromide (ALT 711) reduced transdifferentiation in diabetic rats in association with reduced tubular AGE and TGF-beta expression. This study provides a novel mechanism to explain the development of tubulointerstitial disease in diabetic nephropathy and provides a new treatment target.

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.

Measurement of TIMP-3 expression and Bruch's membrane thickness in human macula

An increase or accumulation in tissue inhibitor of matrix metalloproteinases-3 (TIMP-3) protein in Bruch's membrane with ageing in normal eyes, and in age related macular degeneration (AMD) has been previously demonstrated. The purpose of this study was to determine whether the expression of TIMP-3 mRNA increases with age, and to define any relationship between altered expression and Bruch's membrane thickness. Normal eyes were obtained from 30 donors (age range 15-90 years). Full-thickness 8 mm macular punches centred on the fovea were taken to allow removal of the chorioretinal complex, for subsequent nucleic acid extraction. Samples were normalized for RNA degradation using beta-actin reverse transcriptase-polymerase chain reaction (RT-PCR). A competitive RT-PCR was then used to allow measurement of TIMP-3 gene expression in each sample. The tissue adjacent to that used for nucleic acid extraction was processed histologically to allow determination of Bruch's membrane thickness. Bruch's membrane thickness was found to increase with age (P < 0.01), but TIMP-3 expression, as measured by competitive RT-PCR, was not significantly increased with age (P = 0.19). An inverse correlation was noted between TIMP-3 expression and Bruch's membrane thickness after controlling for age (P = 0.032). The results of this study suggest that TIMP-3 expression does not alter significantly with age. Therefore, accumulation of the TIMP-3 protein must occur by a mechanism other than increased expression. TIMP-3 protein levels may still prove to contribute to events associated with ageing in the macula, such as matrix remodelling in Bruch's membrane. Further studies are required to elucidate the precise interactions and turnover of the TIMP-3 protein, and resulting changes in the control of matrix metalloproteinase activity in the ageing macula.

Antidiabetic effect of an acidic polysaccharide (TAP) from Tremella aurantia and its degradation product (TAP-H)

Continuous oral administration of the acidic polysaccharide (TAP) solution (0.5 g/l) and the TAP-H (degradation products of TAP) solution (1.5 g/l) instead of water for 10 weeks were found to depress plasma glucose increases in diabetes using genetically non-insulin-dependent diabetic model (KK-Ay) mice. TAP and TAP-H significantly lowered levels of insulin, total-cholesterol and triglyceride in the blood of the mice. In excretion to feces, TAP and TAP-H significantly increased the total bile acid, while the cholesterol content of both groups was less than that of the control. Furthermore, TAP and TAP-H significantly decreased the plasma lipoperoxide level. The study shows that TAP and TAP-H have an antidiabetic effect on diabetes model mice.

Endogenous heparin activity deficiency: the 'missing link' in atherogenesis?

This paper reviews published studies since 1995 dealing with many atherogenic mechanisms where exogenous heparin was beneficial. In these areas endogenous heparin deficiency is likely to be harmful. Mechanisms included inflammatory factors, lower endogenous plasma heparin levels, lipoprotein lipase, chemokines, APOE e4, lipoprotein(a), among others. Demonstrated reduction of heparan sulfate proteoglycans (HSPG) and of endogenous plasma heparin was reviewed.

Oxidative stress in diabetic nephropathy: basic and clinical information

Oxidative stress has been known to play an important role in the development and progression of diabetic nephropathy, but the intracellular signal transduction pathways regulated by reactive oxygen species (ROS) have not been clearly defined. High glucose (HG) induces intracellular ROS directly via glucose metabolism and auto-oxidation and indirectly through the formation of advanced glycation end products and their receptor binding. ROS mimic the stimulatory effects of HG and upregulate transforming growth factor-beta 1, plasminogen activator inhibitor-1, and extracellular matrix (ECM) proteins by glomerular mesangial cells, thus leading to mesangial expansion. ROS activate other signaling molecules, such as protein kinase C and mitogen-activated protein kinases and transcription factors, such as nuclear factor-kappa B, activator protein-1, and specificity protein 1 leading to transcription of genes encoding cytokines, growth factors, and ECM proteins. Finally, various antioxidants inhibit mesangial cell activation by HG and ameliorate features of diabetic nephropathy. These findings qualify ROS as intracellular messengers and as integral glucose-signaling molecules in glomerular mesangial cells in diabetic nephropathy. With this new concept, ROS assume a greater importance in the pathogenesis of diabetic nephropathy. Future studies elucidating other downstream-signaling molecules activated by ROS in mesangial and other renal cells will allow us to understand the final cellular responses to HG, such as proliferation, differentiation, apoptosis, and ECM accumulation. With this new information, we should be able to develop strategies for a more rational treatment of diabetic nephropathy.

Oxidative stress markers in Korean subjects with insulin resistance syndrome

Insulin resistance syndrome (IRS) is a cluster of prevalent conditions including glucose intolerance, hypertension and dyslipidemia, which commonly predispose to cardiovascular disease. However, the mechanism by which IRS is related with cardiovascular disease is not yet settled. Recently, it has been hypothesized that atherosclerosis is an inflammatory disease and that an increase in oxidative stress plays a key role in causing endothelial dysfunction associated with atherosclerosis. There has been, however, no study directly relating IRS with oxidative stress in human subjects. We measured various markers of oxidative stress among subjects who participated in a population-based epidemiological study performed in 1996. IRS was defined as non-diabetic subjects having more than two of three salient features of the syndrome (glucose intolerance, hypertriglyceridemia/low high density lipoprotein (HDL)-cholesterol and hypertension). The subjects with IRS (n=70) showed higher plasma malondialdehyde (MDA; 2.10+/-1.43 vs. 1.63+/-1.21 micromol/ml, P=0.009), homocysteine (16.32+/-8.34 vs. 13.06+/-6.49 micromol/l, P=0.002) and ceruloplasmin concentrations (29.80+/-5.28 vs. 27.39+/-5.10 mg/dl, P=0.002) than control subjects (n=196). Plasma MDA concentration was positively correlated with waist-to-hip ratio (r=0.124, P=0.044), and with plasma triglyceride (TG; r=0.163, P=0.008), ferritin (r=0.200, P=0.002) and homocysteine concentrations (r=0.136, P=0.032). These results suggest that increase in oxidative stress may contribute to the development of cardiovascular disease in IRS.

Anti-inflammatory antioxidants attenuate the expression of inducible nitric oxide synthase mediated by advanced glycation endproducts in murine microglia

Advanced glycation endproducts (AGEs) accumulate on long-lived protein deposits including beta-amyloid plaques in Alzheimer's disease (AD). AGE-modified amyloid deposits contain oxidized and nitrated proteins as markers of a chronic neuroinflammatory condition and are surrounded by activated microglial and astroglial cells. We show in this study that AGEs increase nitric oxide production by induction of the inducible nitric oxide synthase (iNOS) on the mRNA and protein level in the murine microglial cell line N-11. Membrane permeable antioxidants including oestrogen derivatives (e.g. 17beta-oestradiol) thiol antioxidants (e.g. (R+)-alpha-lipoic acid) and Gingko biloba extract EGb 761, but not phosphodiesterase inhibitors such as propentophylline, prevent the up-regulation of AGE-induced iNOS expression and NO production. These results indicate that oxygen free radicals serve as second messengers in AGE-induced pro-inflammatory signal transduction pathways. As this pharmacological mechanism is not only relevant for Alzheimer's disease, but also for many chronic inflammatory conditions, such membrane-permeable antioxidants could be regarded not only as antioxidant, but also as potent therapeutic anti-inflammatory drugs.

Diabetes-associated sustained activation of the transcription factor nuclear factor-kappaB

Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) has been suggested to participate in chronic disorders, such as diabetes and its complications. In contrast to the short and transient activation of NF-kappaB in vitro, we observed a long-lasting sustained activation of NF-kappaB in the absence of decreased IkappaBalpha in mononuclear cells from patients with type 1 diabetes. This was associated with increased transcription of NF-kappaBp65. A comparable increase in NF-kappaBp65 antigen and mRNA was also observed in vascular endothelial cells of diabetic rats. As a mechanism, we propose that binding of ligands such as advanced glycosylation end products (AGEs), members of the S100 family, or amyloid-beta peptide (Abeta) to the transmembrane receptor for AGE (RAGE) results in protein synthesis-dependent sustained activation of NF-kappaB both in vitro and in vivo. Infusion of AGE-albumin into mice bearing a beta-globin reporter transgene under control of NF-kappaB also resulted in prolonged expression of the reporter transgene. In vitro studies showed that RAGE-expressing cells induced sustained translocation of NF-kappaB (p50/p65) from the cytoplasm into the nucleus for >1 week. Sustained NF-kappaB activation by ligands of RAGE was mediated by initial degradation of IkappaB proteins followed by new synthesis of NF-kappaBp65 mRNA and protein in the presence of newly synthesized IkappaBalpha and IkappaBbeta. These data demonstrate that ligands of RAGE can induce sustained activation of NF-kappaB as a result of increased levels of de novo synthesized NF-kappaBp65 overriding endogenous negative feedback mechanisms and thus might contribute to the persistent NF-kappaB activation observed in hyperglycemia and possibly other chronic diseases.

Advanced glycation endproducts co-localize with inducible nitric oxide synthase in Alzheimer's disease

Advanced glycation endproducts (AGEs), protein-bound oxidation products of sugars, have been shown to be involved in the pathophysiological processes of Alzheimer's disease (AD). AGEs induce the expression of various pro-inflammatory cytokines and the inducible nitric oxide synthase (iNOS) leading to a state of oxidative stress. AGE modification and resulting crosslinking of protein deposits such as amyloid plaques may contribute to the oxidative stress occurring in AD. The aim of this study was to immunohistochemically compare the localization of AGEs and beta-amyloid (Abeta) with iNOS in the temporal cortex (Area 22) of normal and AD brains. In aged normal individuals as well as early stage AD brains (i.e. no pathological findings in isocortical areas), a few astrocytes showed co-localization of AGE and iNOS in the upper neuronal layers, compared with no astrocytes detected in young controls. In late AD brains, there was a much denser accumulation of astrocytes co-localized with AGE and iNOS in the deeper and particularly upper neuronal layers. Also, numerous neurons with diffuse AGE but not iNOS reactivity and some AGE and iNOS-positive microglia were demonstrated, compared with only a few AGE-reactive neurons and no microglia in controls. Finally, astrocytes co-localized with AGE and iNOS as well as AGE and were found surrounding mature but not diffuse amyloid plaques in the AD brain. Our results show that AGE-positive astrocytes and microglia in the AD brain express iNOS and support the evidence of an AGE-induced oxidative stress occurring in the vicinity of the characteristic lesions of AD. Hence activation of microglia and astrocytes by AGEs with subsequent oxidative stress and cytokine release may be an important progression factor in AD.

Regulation of vascular endothelial growth factor expression by advanced glycation end products

Advanced glycation end products (AGEs) are generated during long term diabetes and are correlated with the development of diabetic complications, such as retinopathy. Diabetic retinopathy is characterized by an increased retinal neovascularization due to the action of the angiogenic factor, vascular endothelial growth factor (VEGF). In this report, we show that injection of insulin and glycated albumin (Alb-AGE) to mice increases VEGF mRNA expression in eyes. Insulin and Alb-AGE stimulate VEGF mRNA and protein expression in retinal epithelial cells (ARPE-19). Alb-AGE-induced VEGF expression is not modulated by the use of antioxidants, N-acetyl-l-cysteine or pyrrolidinedithiocarbamate, or by an inhibitor of phosphatidylinositol 3-kinase (PI3K), wortmannin. However, using an inhibitor of ERK activation, U0126, we show that Alb-AGE stimulates VEGF expression through an ERK-dependent pathway. Accordingly, we found that Alb-AGE activated mitogen-activate protein kinase, ERK1/2, JNK1/2, but not p38, and that Alb-AGE did not activate PI3K and PKB. Moreover, Alb-AGE activated the transcription factor, hypoxia inducible factor-1 (HIF-1) DNA binding activity. This activation is mediated by an increase in accumulation of the HIF-1alpha protein through an ERK-dependent pathway. Thus, stimulation of VEGF expression by Alb-AGE, through the activation of HIF-1, could play an important role in the development of diabetic retinopathy.

RAGE expression and AGE-induced MAP kinase activation in Caco-2 cells

RAGE (receptor for advanced glycation end products) is a multiligand cell surface molecule of the immunoglobulin superfamily. It was originally described as a receptor for protein adducts formed by glycoxidation (AGEs) that accumulate in diseases such as diabetes and renal failure. Performing RT-PCR and Western blot analysis we intended to determine RAGE expression in the human colon adenocarcinoma cell line Caco-2. Moreover, Caco-2 cells were incubated in the presence of AGEs. Since RAGE ligation triggers the p21(ras) signal transduction pathway the activation state of p44/42 (ERK1/2) MAP kinases was determined. Here we demonstrate for the first time that Caco-2 cells express RAGE and that administration of the food-derived casein-linked AGE N(epsilon)-(carboxymethyl)lysine (Cas-CML) results in Caco-2 p44/42 (ERK1/2) MAP kinase activation.

Taurine counteracts oxidative stress and nerve growth factor deficit in early experimental diabetic neuropathy

Oxidative stress has a key role in the pathogenesis of diabetic complications. We have previously reported that taurine (T), which is known to counteract oxidative stress in tissues (lens, kidney, retina) of diabetic rats, attenuates nerve blood flow and conduction deficits in early experimental diabetic neuropathy (EDN). The purpose of this study was to evaluate whether dietary T supplementation counteracts oxidative stress and the nerve growth factor (NGF) deficit in the diabetic peripheral nerve. The experiments were performed in control rats and streptozotocin-diabetic rats fed standard or 1% T-supplemented diets for 6 weeks. All measurements were performed in the sciatic nerve. Malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HA) were quantified with N-methyl-2-phenylindole. GSH, GSSG, dehydroascorbate (DHAA), and ascorbate (AA) were assayed spectrofluorometrically, T by reverse-phase HPLC, and NGF by ELISA. MDA plus 4-HA concentration (mean +/- SEM) was increased in diabetic rats (0.127 +/- 0.006 vs 0.053 +/- 0.003 micromol/g in controls, P < 0.01), and this increase was partially prevented by T (0.096 +/- 0.004, P < 0.01 vs untreated diabetic group). GSH levels were similarly decreased in diabetic rats treated with or without taurine vs controls. GSSG levels were similar in control and diabetic rats but were lower in diabetic rats treated with T (P < 0.05 vs controls). AA levels were decreased in diabetic rats (0.133 +/- 0.015 vs 0.219 +/- 0.023 micromol/g in controls, P < 0.05), and this deficit was prevented by T. DHAA/AA ratio was increased in diabetic rats vs controls (P < 0.05), and this increase was prevented by T. T levels were decreased in diabetic rats (2.7 +/- 0.16 vs 3.8 +/- 0.1 micromol/g in controls, P < 0.05) and were repleted by T supplementation (4.2 +/- 0.3). NGF levels were decreased in diabetic rats (2.35 +/- 0.20 vs 3.57 +/- 0.20 ng/g in controls, P < 0.01), and this decrease was attenuated by T treatment (3.16 +/- 0.28, P < 0.05 vs diabetic group). In conclusion, T counteracts oxidative stress and the NGF deficit in early EDN. Antioxidant effects of T in peripheral nerve are, at least in part, mediated through the ascorbate system of antioxidative defense. The findings are consistent with the important role for oxidative stress in impaired neurotrophic support in EDN.

Heme oxygenase-1 inhibits atherogenesis in Watanabe heritable hyperlipidemic rabbits

BACKGROUND

Heme oxygenase-1 (HO-1) is proposed to have a variety of adaptive responses against oxidative stress. To examine the function of HO-1 against atherogenesis in vivo, we observed the effects of HO-1 inhibition on atherosclerotic lesion formation in Watanabe heritable hyperlipidemic rabbits (WHHL). Methods and Results- During 4 weeks of a 1% cholesterol diet, intravenous injections of Sn-protoporphyrin IX to inhibit HO-1 (S group, n=10) and saline as a control (C group, n=10) were given to 3-month-old WHHL rabbits. The percentages of en face atherosclerotic lesion areas in total descending aorta by Sudan IV staining (EFA) and the ratio of intima to media in microscopic atherosclerotic lesions in the ascending aortas (I/M) were calculated. Two different quantitative methods revealed significantly greater atherosclerotic lesions in the S group than the C group (EFA, P<0.001; I/M, P<0.005). HO-1 expression in atherosclerotic lesions was confirmed by Northern blot and immunohistochemical analyses. The dominant cell types expressing HO-1 were macrophages and foam cells, in which oxidized phospholipids were also accumulated. HO inhibition increased plasma and tissue lipid peroxide levels without affecting plasma lipid co osition.

CONCLUSIONS

These results suggest the possibilities that HO-1 has antiatherogenic properties in vivo and that the antiatherogenic properties of HO-1 are conducted through the prevention of lipid peroxidation.

Modulation of glyoxalase, glutathione S-transferase and antioxidant enzymes in the liver, spleen and erythrocytes of mice by dietary administration of fenugreek seeds

There is a growing interest in understanding the biological effect of time-tested folk medicinal plants. In the present work, the effect of dietary administration of fenugreek seeds on the glyoxalase system and antioxidant enzymes as well as levels of glutathione (GSH) have been examined in different tissues of mice. Swiss albino mice were fed with diet containing powdered fenugreek for 4 weeks. The mode and magnitude of effect was found to depend on the dose of fenugreek and type of tissue. The diet containing 1 and 2% of fenugreek enhanced the specific activity of gly I, whereas 5 and 10% inhibited its activity in the liver. However, on the other hand, the specific activity of gly II decreased continuously with dose. Dietary administration of fenugreek seeds resulted in an increase of GSH levels and the glutathione S-transferase (GST) activity in the liver. Fenugreek (1 and 2%) showed no appreciable change in superoxide dismutase (SOD) and catalase. However, 5 and 10% doses of fenugreek supplementation inhibited their activities. In the case of spleen, a significant change in gly I was observed only at 10% fenugreek. In addition, a significant increase was also observed with GSH levels. Fenugreek treatment up to 5% showed a small but consistent increase in erythrocytes. In the case of GST, the activity enhanced with dose. Significant elevation of catalase activity was observed with a 10% dose of fenugreek. The significance and relevance of these findings are suggested in relation to mechanistic aspects.

Heterogeneity affecting outcome from acute stroke therapy: making reperfusion worse

BACKGROUND

Stroke patients are heterogeneous not only with respect to etiology but also in terms of preexisting clinical conditions. Approximately one fifth of patients with acute stroke are hyperglycemic and/or have had a recent infectious or inflammatory condition. Summary of Review-- Experimental research indicates that these factors can alter and accelerate the evolution of stroke and reperfusion injury, although these effects are complex and some may have a favorable impact. Both conditions involve activation of inflammatory and reactive oxygen mechanisms. In addition, hyperglycemia has concomitant deleterious vascular and metabolic effects that worsen infarct size and encourage hemorrhagic transformation in reperfusion models. Clinical data are less extensive but in general support an adverse impact on outcome.

CONCLUSIONS

After examining these data in detail, we concluded that the presence of these clinical conditions could assist in identification of those at increased risk for complications of reperfusion therapy. Furthermore, consideration of these factors may provide a rational basis for combination therapy and improve the clinical relevance of experimental stroke models.

High glucose and advanced glycation end products induce phospholipid hydrolysis and phospholipid enzyme inhibition in bovine retinal pericytes

In the present study, we investigated the possible role of oxidative stress and the modulation of phospholipid turnover in two related models of pericyte injury, i.e., treatment with high glucose or advanced glycation end products (AGEs). Growing microcapillary pericytes from bovine retinas in culture were incubated, for 3 weeks, with 20-50 mM glucose or 2-20 microM AGEs, and peroxidation parameters (malondialdehyde, conjugated diene, hydroperoxide, glutathione (GSH) levels and lactate dehydrogenase (LDH) release) were evaluated. Arachidonate (AA) and choline release from membrane phospholipids was determined in pericytes prelabeled with [1-(14)C]arachidonate and [Me-(3)H]choline, respectively, and stimulated with elevated glucose or AGEs for 30 min or 2 h. [1-(14)C]arachidonate and [Me-(3)H]choline incorporation into phospholipids, for 2 h and 3 h respectively, was also studied in conditioned and serum-starved cultures. Finally, lysates of treated and control cells were assayed for cytosolic phospholipase A(2) (cPLA(2)), acyl-CoA:1-acyl-sn-glycero-3-phosphocholine O-acyltransferase (AT), CTP:phosphocholine cytidylyltransferase (CT) and microsomal choline phosphotransferase (CPT) enzyme activities. We found that high glucose and AGEs caused neither significant production of reactive oxygen species nor cell toxicity or death, unlike other cell types. Both agents had no significant effect on the cellular ultrastructure, evaluated by light and electron microscopy, AA incorporation and release, cytosolic phospholipase A(2) (cPLA(2)) and AT activities. On the contrary, choline incorporation into phosphatidylcholine, CT and CPT activities were significantly reduced either by 50 mM glucose or 20 microM AGEs. Simultaneously, [Me-(3)H]choline release was significantly stimulated by both agents. We conclude that prolonged treatments with high glucose or AGEs are not able to induce oxidative injury in bovine retinal capillary pericytes. Nevertheless, they do induce phospholipid hydrolysis and phospholipid enzyme activity inhibition.

Involvement of microglial receptor for advanced glycation endproducts (RAGE) in Alzheimer's disease: identification of a cellular activation mechanism

Receptor-mediated interactions with amyloid beta-peptide (Abeta) could be important in the evolution of the inflammatory processes and cellular dysfunction that are prominent in Alzheimer's disease (AD) pathology. One candidate receptor is the receptor for advanced glycation endproducts (RAGE), which can bind Abeta and transduce signals leading to cellular activation. Data are presented showing a potential mechanism for Abeta activation of microglia that could be mediated by RAGE and macrophage colony-stimulating factor (M-CSF). Using brain tissue from AD and nondemented (ND) individuals, RAGE expression was shown to be present on microglia and neurons of the hippocampus, entorhinal cortex, and superior frontal gyrus. The presence of increased numbers of RAGE-immunoreactive microglia in AD led us to further analyze RAGE-related properties of these cells cultured from AD and ND brains. Direct addition of Abeta(1-42) to the microglia increased their expression of M-CSF. This effect was significantly greater in microglia derived from AD brains compared to those from ND brains. Increased M-CSF secretion was also demonstrated using a cell culture model of plaques whereby microglia were cultured in wells containing focal deposits of immobilized Abeta(1-42). In each case, the Abeta stimulation of M-CSF secretion was significantly blocked by treatment of cultures with anti-RAGE F(ab')2. Treatment of microglia with anti-RAGE F(ab')2 also inhibited the chemotactic response of microglia toward Abeta(1-42). Finally, incubation of microglia with M-CSF and Abeta increased expression of RAGE mRNA. These microglia also expressed M-CSF receptor mRNA. These data suggest a positive feedback loop in which Abeta-RAGE-mediated microglial activation enhances expression of M-CSF and RAGE, possibly initiating an ascending spiral of cellular activation.

Overexpression of Cu2+/Zn2+ superoxide dismutase protects against early diabetic glomerular injury in transgenic mice

Ex vivo and in vitro observations implicate superoxide as a mediator of cell injury in diabetes, but in vivo evidence is lacking. In the current studies, parameters of glomerular injury were examined in hemizygous nondiabetic transgenic mice (SOD) and streptozotocin-diabetic (D) transgenic mice (D-SOD), which overexpress human cytoplasmic Cu2+/Zn2+ superoxide dismutase (SOD-1), and in corresponding wild-type littermates (WT, D-WT) after 4 months of diabetes. In both SOD and D-SOD mice, renal cortical SOD-1 activity was twofold higher than values in the WT mice; blood glucose and glycosylated hemoglobin (GHb) levels did not differ in the two diabetic groups. Urinary albumin excretion, fractional albumin clearance, urinary transforming growth factor-beta (TGF-beta) excretion, glomerular volume, glomerular content of immunoreactive TGF-beta, and collagen alpha1 (IV) and renal cortical malondialdehyde (MDA) levels were significantly higher in D-WT mice compared with corresponding values in D-SOD mice. Glomerular volume, glomerular content of TGF-beta and collagen IV, renal cortical MDA, and urinary excretion of TGF-beta in D-SOD mice did not differ significantly from corresponding values in either the nondiabetic SOD or WT mice. In separate groups of mice studied after 8 months of diabetes, mesangial matrix area, calculated as a fraction of total glomerular tuft area, and plasma creatinine were significantly higher in D-WT but not in D-SOD mice, compared with corresponding values in the nondiabetic mice. In vitro infection of mesangial cells (MC) with a recombinant adenovirus encoding human SOD-1 increased SOD-1 activity threefold over control cells and prevented the reduction of aconitase activity, an index of cellular superoxide, and the increase in collagen synthesis that otherwise occurred in control MC in response to culture with 300 or 500 mg/dl glucose. Thus, increases in cellular SOD-1 activity attenuate diabetic renal injury in vivo and also prevent stimulation of MC matrix protein synthesis induced in vitro by high glucose.

Therapeutic potential of anti-oxidants and diabetic retinopathy

Retinopathy, a severely disabling complication of diabetes mellitus, is today the leading cause of acquired blindness among young adults in developed countries. Good glycaemic control can attenuate the development of diabetic retinopathy but such metabolic control is often difficult to achieve and maintain and additional therapies need to be identified by which retinopathy can be prevented or arrested. Hyperglycaemia plays a critical role in the development and progression of retinopathy, but the mechanism by which hyperglycaemia results in the development of retinopathy is not clear. Oxidative stress is increased in the retina in diabetes. The possible sources of increased oxidative stress might include increased generation of free radicals or impaired anti-oxidant defence system. Dietary supplementation with anti-oxidants in animal models of diabetic retinopathy inhibits retinal metabolic abnormalities and retinal histopathology, suggesting that oxidative stress is associated with the development of retinopathy. The mechanism by which anti-oxidants inhibit retinopathy in diabetes warrants further investigation, but animal studies show that increasing the diversity of anti-oxidants provides significantly more protection than using any single anti-oxidant. Thus, supplementation with anti-oxidants represents an achievable adjunct therapy to help preserve vision in diabetic patients.

Beneficial effect of troglitazone, an insulin-sensitizing antidiabetic agent, on coronary circulation in patients with non-insulin-dependent diabetes mellitus

Evidence is increasing for small vessel remodeling and disturbance of endothelium-dependent vasodilation in diabetic patients. Insulin increases vascular wall thickening and produces endothelial dysfunction. Troglitazone, a new insulin-sensitizer antidiabetic agent, is considered to reduce plasma insulin level and the present study assessed its effect on the coronary circulation of the patients with non-insulin-dependent diabetes mellitus (NIDDM). Analysis of the myocardial washout rate with adenosine triphosphate-stress thallium-201 scintigraphy was used to estimate coronary circulation, and for estimation of insulin sensitivity, the homeostasis model insulin resistance index (HOMA-R) was calculated. Patients were treated with monotherapy of either troglitazone (200 mg bid, n=12) or glibenclamide (2.5 mg daily, n=12) for 3 months. Age-, sex- and risk factors-matched subjects without NIDDM were employed as a control. Fasting plasma glucose and hemoglobin A1c were similarly decreased by troglitazone or glibenclamide. Plasma insulin level (pmol/L) decreased from 66.6+/-10.8 to 39.0+/-7.2 with troglitazone, but was unchanged by glibenclamide (58.8+/-7.2 to 66.0+/-10.8). The diabetic groups had a significantly lower washout rate than controls, which was improved by troglitazone, but not by glibenclamide. In addition, the increase in washout rate correlated significantly with the decrease in HOMA-R in the troglitazone group. In conclusion, troglitazone can restore coronary circulation by improving insulin resistance in patients with NIDDM.

Requirement for p38 and p44/p42 mitogen-activated protein kinases in RAGE-mediated nuclear factor-kappaB transcriptional activation and cytokine secretion

Advanced glycation end product (AGE) activation of the signal-transducing receptor for AGE (RAGE) has been linked to a proinflammatory phenotypic change within cells. However, the precise intracellular signaling pathways involved have not been elucidated. We demonstrate here that human serum albumin modified with N(epsilon)-(carboxymethyl)lysine (CML), a major AGE adduct that progressively accumulates with aging, diabetes, and renal failure, induced nuclear factor (NF)-kappaB-driven reporter gene expression in human monocytic THP-1 cells. The NF-kappaB response was blocked with a synthetic peptide corresponding to the putative ligand-binding domain of RAGE, with anti-RAGE antiserum, and by coexpression of truncated receptors lacking the intracellular domain. Signal transduction from RAGE to NF-kappaB involved the generation of reactive oxygen species, since reporter gene expression was blocked with the antioxidant N-acetyl-L-cysteine. CML-modified albumin produced rapid transient activation of tyrosine phosphorylation, extracellular signal-regulated kinase 1 and 2, and p38 mitogen-activated protein kinase (MAPK), but not c-Jun NH(2)-terminal kinase. RAGE-mediated NF-kappaB activation was suppressed by the selective p38 MAPK inhibitor SB203580 and by coexpression of a kinase-dead p38 dominant-negative mutant. Activation of NF-kappaB by CML-modified albumin increased secretion of proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1beta, and monocyte chemoattractant protein-1) severalfold, and inhibition of p38 MAPK blocked these increases. These results indicate that p38 MAPK activation mediates RAGE-induced NF-kappaB-dependent secretion of proinflammatory cytokines and suggest that accelerated inflammation may be a consequence of cellular activation induced by this receptor.

Oxidative stress and increased expression of growth factors in lesions of failed hemodialysis access

The pathological role of oxidative stress in patients treated by hemodialysis has gained increasing recognition in recent years. Because complications related to vascular access are a major source of morbidity, immunohistochemical evidence of oxidative stress and activation of growth factors were examined in native arteriovenous (AV) fistulae (n = 11) and expanded polytetrafluoroethylene (ePTFE) grafts (n = 15) recovered from hemodialysis patients at the time of surgical revision or resection. To show the presence of oxidative stress in tissues, three markers were chosen: N(epsilon)(carboxymethyl)lysine, a structurally identified advanced glycation end product; 4-hydroxy-2,3-nonenol, a lipid peroxidation product; and redox-active transition metals bound to proteins, a source of Fenton chemistry-generated free radicals. Markers of cell growth and proliferation were endothelin-1 (ET-1), a potent mitogenic peptide implicated in the formation of intimal hyperplasia; transforming growth factor-beta (TGF-beta), a stimulus to vascular cell growth and matrix production; and platelet-derived growth factor (PDGF), a mediator of intimal hyperplasia. All specimens studied showed significant intimal hyperplasia. In general, the neointima close to the vascular lumen of the AV fistula and the pseudointima close to the lumen of the ePTFE graft were positive for oxidative stress markers. At sites of injury, especially in the presence of histological evidence of inflammation and healing, expression of oxidative markers was particularly intense. Prominent staining of PDGF was shown at sites of anastomotic hyperplasia and in neovasculature. TGF-beta was associated with proliferation or repair in both AV fistulae and ePTFE grafts. ET-1 staining was most intense in the neointima and pseudointima. This study showed histochemical colocalization of markers of oxidative stress with growth factors known to contribute to intimal hyperplasia.

Impairment of coronary microvascular dilation in response to cold pressor--induced sympathetic stimulation in type 2 diabetic patients with abnormal stress thallium imaging

Coronary microcirculation dysfunction may be associated with myocardial perfusion defects on thallium imaging in diabetic patients without coronary artery stenosis. Microvascular coronary adaptation to increased myocardial oxygen demand in response to sympathetic stimulation evoked by the cold pressor test was examined in 22 type 2 diabetic patients with thallium imaging defects and in 15 control subjects. Both the diabetic patients and control subjects had angiographically normal coronary arteries and no other risk factors. Despite a similar increase in the rate-pressure product in the two groups (22.6 +/- 12.4% in diabetic patients and 31.8 +/- 8.2% in control subjects, NS), coronary blood flow increase in the left anterior descending artery (mean flow velocity measured by intracoronary Doppler multiplied by the cross-sectional area measured by digital angiography) was significantly lower in diabetic patients than in control subjects (14.7 +/- 19.8 vs. 75.5 +/- 13.5%, respectively; P = 0.0001). In addition, when there was a positive correlation between the two parameters in control subjects (r = 0.651, P < 0.01), there was no relationship in diabetic patients (r = 0.054). In conclusion, vasodilation of the coronary microcirculation in response to sympathetic stimulation evoked by the cold pressor test is impaired in type 2 diabetic patients without epicardial artery lesions. This microvascular impairment during sympathetic stimulation may explain exercise-induced myocardial perfusion abnormalities observed in these patients and may impair microcirculatory coronary vasodilation during current life stress episodes such as exercise, mental stress, or cold exposition.

Activation of NADPH oxidase by AGE links oxidant stress to altered gene expression via RAGE

Engagement of the receptor for advanced glycation end products (RAGE) by products of nonenzymatic glycation/oxidation triggers the generation of reactive oxygen species (ROS), thereby altering gene expression. Because dissection of the precise events by which ROS are generated via RAGE is relevant to the pathogenesis of complications in AGE-related disorders, such as diabetes and renal failure, we tested the hypothesis that activation of NADPH oxidase contributed, at least in part, to enhancing oxidant stress via RAGE. Here we show that incubation of human endothelial cells with AGEs on the surface of diabetic red blood cells, or specific AGEs, (carboxymethyl)lysine (CML)-modified adducts, prompted intracellular generation of hydrogen peroxide, cell surface expression of vascular cell adhesion molecule-1, and generation of tissue factor in a manner suppressed by treatment with diphenyliodonium, but not by inhibitors of nitric oxide. Consistent with an important role for NADPH oxidase, although macrophages derived from wild-type mice expressed enhanced levels of tissue factor upon stimulation with AGE, macrophages derived from mice deficient in a central subunit of NADPH oxidase, gp91phox, failed to display enhanced tissue factor in the presence of AGE. These findings underscore a central role of NADPH oxidase in AGE-RAGE-mediated generation of ROS and provide a mechanism for altered gene expression in AGE-related disorders.

Role of oxidative stress in the apoptotic cell death of cultured cerebellar granule neurons

When cultured cerebellar granule neurons (CGN) are transferred from 25 mM KCl (K25) to 5 mM KCl (K5) caspase-3 and caspase-8, but not caspase-1 or caspase-9,activities are induced and cells die apoptotically. CGN death was triggered by a [Ca(2+)](i) modification when [Ca(2+)](i) was reduced from 300 nM to 50 nM in a K5 medium. The [Ca(2+)](i) changes were followed by an increase in ROS levels. The generation of both cytosolic and mitochondrial reactive oxygen species (ROS) occurred at three different times, 10 min, 30 min and 3--4 hr but only those ROS produced after 3--4 hr are involved in the process of cell death. When CGN cultured in a K5 medium are treated with different antioxidants like scavengers of ROS (mannitol, DMSO) or antioxidant enzymes (superoxide dismutase and catalase) phosphatidylserine translocation, caspase activity, chromatin condensation and cell death is markedly diminished. The protective effect of antioxidants is not mediated through a modification in [Ca(2+)](i). Caspase activation, PS translocation and chromatin condensation were downstream of ROS production. In contrast to H(2)O(2), ROS produced by a xanthine/xanthine oxidase system in CGN cultured in K25 were able to directly induce caspase-3 activation and death that resulted sensitive to z-VAD, a caspase inhibitor. These findings indicate that a reduction in [Ca(2+)](i) triggers CGN death by inducing a generation of ROS after 3--4 hr, which could play a critical role in the initial phases of the apoptotic process including PS translocation, chromatin condensation and the activation of initiator and executor caspases.

The role of oxidative stress in the onset and progression of diabetes and its complications: a summary of a Congress Series sponsored by UNESCO-MCBN, the American Diabetes Association and the German Diabetes Society

This review summarises the results and discussions of an UNESCO-MCBN supported symposium on oxidative stress and its role in the onset and progression of diabetes. There is convincing experimental and clinical evidence that the generation of reactive oxygen species (ROI) is increased in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Nevertheless there is controversy about which markers of oxidative stress are most reliable and suitable for clinical practice. There are various mechanisms that contribute to the formation of ROI. It is generally accepted that vascular cells and especially the endothelium become one major source of ROI. An important role of oxidative stress for the development of vascular and neurological complications is suggested by experimental and clinical studies. The precise mechanisms by which oxidative stress may accelerate the development of complications in diabetes are only partly known. There is however evidence for a role of protein kinase C, advanced glycation end products (AGE) and activation of transcription factors such as NF kappa B, but the exact signalling pathways and the interactions with ROI remain a matter of discussion. Additionally, results of very recent studies suggest a role for ROI in the development of insulin resistance. ROI interfere with insulin signalling at various levels and are able to inhibit the translocation of GLUT4 in the plasma membrane. Evidence for a protective effect of antioxidants has been presented in experimental studies, but conclusive evidence from patient studies is missing. Large-scale clinical trials such as the DCCT Study or the UKPDS Study are needed to evaluate the long-term effects of antioxidants in diabetic patients and their potential to reduce the medical and socio-economic burden of diabetes and its complications.

Tumor necrosis factor-α is induced through phorbol ester- and glycated human albumin-dependent pathway in THP-1 cells

Tumor necrosis factor-alpha (TNF-alpha) is involved in insulin resistance. Since the fact that peroxisome proliferator-activated receptor gamma (PPARgamma) ligands inhibit the induction of TNF-alpha by phorbol ester, but not by lipopolysaccharide (LPS), suggests two pathways to induce TNF-alpha, we investigated the mechanisms of glycated human albumin (GHA)- or phorbol ester-induced TNF-alpha in THP-1 cells. GHA induced TNF-alpha release in differentiated THP-1 cells, while phorbol ester induced TNF-alpha release in undifferentiated cells but did not induce TNF-alpha in differentiated cells. Forskolin (adenylate cyclase activator) affected more the GHA-induced TNF-alpha release than the phorbol 12-myristate 13-acetate (PMA)-induced one in undifferentiated cells. Staurosporine [protein kinase-C (PK-C) inhibitor] and PD98059 [mitogen-activated protein kinase inhibitor (MAPK)] only partially inhibited GHA-induced TNF-alpha. Catalase completely inhibited GHA-induced TNF-alpha release; however, superoxide dismutase (SOD) had no effect. These results suggest at least two pathways to induce TNF-alpha (phorbol ester- and GHA-dependent ways) and that GHA-induced TNF-alpha release is through predominantly catalase-dependent way in differentiated THP-1 cells.

Methods for monitoring oxidative stress, lipid peroxidation and oxidation resistance of lipoproteins

After a brief discussion of lipid peroxidation mechanism and the action of antioxidants and their potential to exhibit prooxidant effects, we give an overview on the clinical relevance of oxidative stress parameters. Many diseases are associated with oxidative stress e.g. by radical damage, among them atherosclerosis, diabetes mellitus, chronic renal failure, rheumatoid arthritis, and neurodegenerative diseases, and in many cases the investigation of parameters of oxidative stress has brought substantial insights into their pathogenesis. We then briefly review methods for the continuous monitoring of lipid peroxidation processes in vitro, which has helped in elucidating their mechanism and in some more detail cover such methods which have been proposed more recently to assess oxidative status and antioxidant activity in biological samples.

Comparative biology of aging in birds: an update

The long life spans and slow aging rates of birds relative to mammals are paradoxical in view of birds' high metabolic rates, body temperatures and blood glucose levels, all of which are predicted to be liabilities by current biochemical theories of aging. Available avian life-table data show that most birds undergo rapid to slow "gradual" senescence. Some seabird species exhibit extremely slow age-related declines in both survival and reproductive output, and even increase reproductive success as they get older. Slow avian senescence is thought to be coupled evolutionarily with delayed maturity and low annual fecundity. Recent research in our lab and others supports the hypothesis that birds have special adaptations for preventing age-related tissue damage caused by reactive oxygen species (ROS) and advanced glycosylation endproducts, or AGEs, as well as an unusual capacity for neurogeneration in brain. Much of this work is in its early stages, however, and reliable biomarkers for comparing avian and mammalian aging need more thorough development.

The oxidative mechanism of heparin interferes with radical production by glucose and reduces the degree of glycooxidative modifications on human serum albumin

Among substances which may prove useful in preventing or reducing the progression of glycooxidative modifications of proteins, heparin plays a unique role. To elucidate the mechanism whereby heparin may favourably influence the protein structure during glycation, human serum albumin (HSA) was glycated with both 25 and 50 mM glucose in the absence and presence of 12 microg.mL(-1) low-molecular-mass heparin. Glycation caused: (a) modifications of fluorescence emission and excitation spectra consistent with the covalent attachment of glucose to protein; (b) a significant increase in the esterase activity of HSA on p-nitrophenyl acetate; (c) a reduced susceptibility to tryptic digestion and (d) enhanced formation of high-molecular mass aggregates of HSA. These alterations were accompanied by oxidative reactions, as the EPR spectra showed a clear-cut radical signal, dependent on glucose concentration, further confirmed by measurement of the carbonyl content of HSA, as an indirect proof of oxidative damage. In the presence of heparin all the above alterations, especially at 25 mM glucose, turned out to be antagonized. The effects of heparin were dependent on its specific binding to HSA, which triggered an oxidative mechanism strikingly different from that caused by glucose. In the presence of heparin, only the radical species catalyzed by heparin was detected across all samples of glycated HSA, irrespective of glucose concentration. In addition, at 25 mM glucose, enhancement of the oxidative capacity of heparin was also observed. The results demonstrate that the oxidative mechanism sustained by heparin mediates biological effects that may be beneficial in reducing the extent of glycooxidative damage on HSA.

beta(2)-Microglobulin modified with advanced glycation end products delays monocyte apoptosis

BACKGROUND

A local inflammatory reaction to beta(2)-microglobulin (beta(2)m) amyloid deposits by monocytes/macrophages is a characteristic histologic feature of dialysis-related amyloidosis (DRA). Since beta(2)m modified with advanced glycation end products (AGE-beta(2)m) is a major constituent of amyloid in DRA, we tested the hypothesis that AGE-beta(2)m affects apoptosis and phenotype of human monocytes.

METHODS

Human peripheral blood monocytes were incubated with or without in vitro-derived AGE-beta(2)m, and their viability, extent of apoptosis, morphology, and function examined over the subsequent four days.

RESULTS

AGE-modified but not unmodified beta(2)m significantly delayed spontaneous apoptosis of human peripheral blood monocytes in adherent and nonadherent cultures. The effect of AGE-beta(2)m on monocytes apoptosis was time- and dose-dependent and was attenuated by a blocking antibody directed against the human AGE receptor (RAGE). There was no difference in effect between AGE-beta(2)m and that of AGE-modified human serum albumin. Culture of monocytes with AGE-beta(2)m did not alter membrane expression of Fas or Fas ligand. Monocytes cultured with AGE-beta(2)m underwent substantial changes in morphology similar to those observed when monocytes differentiate into macrophages. The cultured cells increased in size and vacuolization, and their content of beta-glucuronidase and acid phosphatase increased by 5- to 10-fold at day 4. Expression of the monocyte--macrophage membrane antigens HLA-DR, CD11b, and CD11c also increased at day 4. Although exhibiting phenotypic characteristics of macrophages, monocytes cultured with AGE-beta(2)m functioned differently than macrophages cultured with serum. Superoxide production in response to phorbol myristic acetate was maintained in monocytes cultured with AGE-beta(2)m, but declined with time in cells cultured with serum. Constitutive synthesis of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2) increased in monocytes cultured for four to six days with AGE-beta(2)m.

CONCLUSIONS

These findings support a novel role for AGE-modified proteins such as AGE-beta(2)m that may contribute to the development of a local inflammatory response, with predominant accumulation of monocytes/macrophages, in DRA.

Therapeutic potential of dietary phase 2 enzyme inducers in ameliorating diseases that have an underlying inflammatory component

Many diseases associated with ageing have an underlying oxidative stress and accompanying inflammatory component, for example, Alzheimer's disease or atherosclerosis. Reviewed in this manuscript are: the role of oxidative stress in activating the transcription factor nuclear factor kappa B (NFκB), the role of NFκB in activating pro-inflammatory gene transcription, strong oxidants produced by cells, anti-oxidant defense systems, the central role of phase 2 enzymes in the anti-oxidant defense, dietary phase 2 enzyme inducers and evidence that dietary phase 2 enzymes decrease oxidative stress. It is likely that a diet containing phase 2 enzyme inducers may ameliorate or even prevent diseases that have a prominent inflammatory component to them. Research should be directed into the potential therapeutic effects of dietary phase 2 enzyme inducers in ameliorating diseases with an underlying oxidative stress and inflammatory component to them.Key words: Alzheimer's disease, atherosclerosis, diet, glutathione, inflammation, stroke.