[Prediction of pathological remission of head and neck squamous cell carcinoma patients after neoadjuvant immunochemotherapy and construction of clinical model based on clinical features and inflammatory markers]

Objective: To analyze the potential clinical biological factors influencing the major pathological response (MPR) to neoadjuvant immunochemotherapy in patients with resectable head and neck squamous cell carcinoma (HNSCC). Methods: This retrospective study enrolled patients with resectable HNSCC who underwent neoadjuvant immunochemotherapy at Sun Yat-sen University Cancer Center from June 1, 2019 to December 31, 2021. Binary logistic regression was used to analyze the correlation between clinical characteristics, inflammatory markers and MPR, and a nomogram model was constructed. The calibration curve and decision curve analysis were used to verify the predictive ability and accuracy of the nomogram model. Results: A total of 173 patients were included in the study, with 141 males and 32 females, aged from 22 to 83 years. After pathological assessment, the patients were divided into two groups: MPR group (108 cases) and non MPR group (65 cases). Logistics regression analysis indicated that the patients with HPV+oropharyngeal cancer, partial response or complete response by imaging assessment, low pre-treatment platelet/lymphocyte ratio, low pre-treatment C reactive protein/albumin ratio and lower pre-and post-treatment C reactive protein/albumin ratio difference were more likely to have MPR (all P<0.05). Nomogram model was constructed based on the above factors, with a C-index of 0.826 (95%CI: 0.760-0.892), and the calibration curve and decision curve analysis confirmed the prediction accuracy of the model. Conclusion: This study shows that many factors are related to MPR of patients with resectable HNSCC receiving neoadjuvant immunochemotherapy and the constructed nomogram model helps to develop personalized treatment strategies for the patients.

[The impact of LDL-C/HDL-C ratio on severity of coronary artery disease and 2-year outcome in patients with premature coronary heart disease: results of a prospective, multicenter, observational cohort study]

Objective: To explore the relationship between low density lipoprotein cholesterol (LDL-C)/high density lipoprotein cholesterol (HDL-C) ratio with the severity of coronary artery disease and 2-yeat outcome in patients with premature coronary heart disease. Methods: This prospective, multicenter, observational cohort study is originated from the PROMISE study. Eighteen thousand seven hundred and one patients with coronary heart disease (CHD) were screened from January 2015 to May 2019. Three thousand eight hundred and sixty-one patients with premature CHD were enrolled in the current study. According to the median LDL-C/HDL-C ratio (2.4), the patients were divided into two groups: low LDL-C/HDL-C group (LDL-C/HDL-C≤2.4, n=1 867) and high LDL-C/HDL-C group (LDL-C/HDL-C>2.4, n=1 994). Baseline data and 2-year major adverse cardiovascular and cerebrovascular events (MACCE) were collected and analyzed in order to find the differences between premature CHD patients at different LDL-C/HDL-C levels, and explore the correlation between LDL-C/HDL-C ratio with the severity of coronary artery disease and MACCE. Results: The average age of the low LDL-C/HDL-C ratio group was (48.5±6.5) years, 1 154 patients were males (61.8%); the average age of high LDL-C/HDL-C ratio group was (46.5±6.8) years, 1 523 were males (76.4%). The number of target lesions, the number of coronary artery lesions, the preoperative SNYTAX score and the proportion of three-vessel coronary artery disease in the high LDL-C/HDL-C group were significantly higher than those in the low LDL-C/HDL-C group (1.04±0.74 vs. 0.97±0.80, P=0.002; 2.04±0.84 vs. 1.85±0.84, P<0.001; 13.81±8.87 vs. 11.70±8.05, P<0.001; 36.2% vs. 27.4%, respectively, P<0.001). Correlation analysis showed that there was a significant positive correlation between LDL-C/HDL-C ratio and preoperative SYNTAX score, the number of coronary artery lesions, the number of target lesions and whether it was a three-vessel coronary artery disease (all P<0.05). The 2-year follow-up results showed that the incidence of MACCE was significantly higher in the high LDL-C/HDL-C group than that in the low LDL-C/HDL-C group (6.9% vs. 9.1%, P=0.011). There was no significant difference in the incidence of all-cause death, cardiac death, myocardial infarction, stroke, revascularization and bleeding between the two groups. Cox multivariate regression analysis showed that the LDL-C/HDL-C ratio has no correlation with 2-year MACCE, death, myocardial infarction, revascularization, stroke and bleeding events above BARC2 in patients with premature CHD. Conclusion: High LDL-C/HDL-C ratio is positively correlated with the severity of coronary artery disease in patients with premature CHD. The incidence of MACCE of patients with high LDL-C/HDL-C ratio is significantly higher during 2 years follow-up; LDL-C/HDL-C ratio may be an indicator for evaluating the severity of coronary artery disease and long-term prognosis in patients with premature CHD.

[Effect of long-term resistance exercise on masseter muscle mechanical hyperalgesia in rats]

OBJECTIVE

To investigate the effect of long-term resistance exercise of hindlimb on mechanical hyperalgesia of bilateral masseter muscle in rats with or without occlusal interference.

METHODS

Six-teen male Sprague-Dawley rats (220-250 g) were randomly divided into four groups: the naive control group, naive exercise group, occlusal interference control group, and occlusal interference exercise group. The rats in occlusal interference groups (occlusal interference control group and occlusal interference exercise group) obtained occlusal interference with 0.4 mm-thick crowns bonded to the right maxillary first molars. The rats in exercise groups (naive exercise group and occlusal interference exercise group) performed squat-type resistance exercises for 30 minutes, once a day, 5 days/week, lasting for 14 weeks. Resistance exercise was recorded every day. Mechanical withdrawal thresholds of bilateral masseter muscle were tested per week by use of modified electronic von-frey anesthesiometer. The rats were weighed per week. After the 14-week exercise, the muscle strength of the hindlimb was tested with a grip strength meter. Muscle (gastrocnemius and soleus) weight of bilateral hindlimb and length of bilateral fibula of the rats were obtained. The muscle-mass/body-mass ratios and muscle-mass/fibula-length ratios were calculated.

RESULTS

Between the naive control group and naive exercise group, there was no significant difference in the mechanical withdrawal thresholds of bilateral masseter muscle for the 0-4 weeks (P>0.05). During the 5-14 weeks, the mechanical withdrawal thresholds of the rats in the naive exercise group were higher than those in the naive control group (P<0.05). Between the occlusal interference control group and occlusal interference exercise group, there was no significant difference in the mechanical withdrawal thresholds of bilateral masseter muscle for the 0-6 weeks (P>0.05). During the 7-14 weeks, the mechanical withdrawal thresholds of rats in the naive exercise group were higher than those in the occlusal interference control group (P<0.05). After the 14week exercise, the body mass of the rats in nonexercise group (the naive control group and occlusal interference control group) were larger than those in exercise group [(462±6) g vs. (418±14) g, P<0.05]. And the muscle strength of hindlimb of the rats in exercise group were bigger than those in non-exercise group [(6.75±0.13) N vs. (5.41±0.15) N, P<0.01].

CONCLUSION

long-term resistance exercise can increase mechanical withdrawal thresholds of the bilateral masseter muscle in rats with or without masseter muscle mechanical hyperalgesia.

Preventing activation of receptor for advanced glycation endproducts in Alzheimer's disease

Receptor for advanced glycation endproducts (RAGE), a member of the immunoglobulin superfamily, is a multi-ligand, cell surface receptor expressed by neurons, microglia, astrocytes, cerebral endothelial cells, pericytes, and smooth muscle cells. At least three major types of the RAGE isoforms (full length, C-truncated, and N-truncated) are present in human brains as a result of alternative splicing. Differential expression of each isoform may play a regulatory role in the physiological and pathophysiological functions of RAGE. Analysis of RAGE expression in non-demented and Alzheimer's disease (AD) brains indicated that increases in RAGE protein and percentage of RAGE-expressing microglia paralleled the severity of disease. Ligands for RAGE in AD include amyloid beta peptide (Abeta), S100/calgranulins, advanced glycation endproduct-modified proteins, and amphoterin. Collective evidence from in vitro and in vivo studies supports that RAGE plays multiple roles in the pathogenesis of AD. The major features of RAGE activation in contributing to AD result from its interaction with Abeta, from the positive feedback mechanisms driven by excess amounts of Abeta, and combined with sustained elevated RAGE expression. The adverse consequences of RAGE interaction with Abeta include perturbation of neuronal properties and functions, amplification of glial inflammatory responses, elevation of oxidative stress and amyloidosis, increased Abeta influx at the blood brain barrier and vascular dysfunction, and induction of autoantibodies. In this article, we will review recent advances of RAGE and RAGE activation based on findings from cell cultures, animal models, and human brains. The potential for targeting RAGE mechanisms as therapeutic strategies for AD will be discussed.

Effect of endothelial cell polarity on beta-amyloid-induced migration of monocytes across normal and AD endothelium

During normal aging and amyloid beta-peptide (Abeta) disorders such as Alzheimer's disease (AD), one finds increased deposition of Abeta and activated monocytes/microglial cells in the brain. Our previous studies show that Abeta interaction with a monolayer of normal human brain microvascular endothelial cells results in increased adherence and transmigration of monocytes. Relatively little is known of the role of Abeta accumulated in the AD brain in mediating trafficking of peripheral blood monocytes (PBM) across the blood-brain barrier (BBB) and concomitant accumulation of monocytes/microglia in the AD brain. In this study, we showed that interaction of Abeta(1--40) with apical surface of monolayer of brain endothelial cells (BEC), derived either from normal or AD individuals, resulted in increased transendothelial migration of monocytic cells (HL-60 and THP-1) and PBM. However, transmigration of monocytes across the BEC monolayer cultivated in a Transwell chamber was increased 2.5-fold when Abeta was added to the basolateral side of AD compared with normal individual BEC. The Abeta-induced transmigration of monocytes was inhibited in both normal and AD-BEC by antibodies to the putative Abeta receptor, receptor for advanced glycation end products (RAGE), and to the endothelial cell junction molecule, platelet-endothelial cell adhesion molecule-1 (PECAM-1). We conclude that interaction of Abeta with the basolateral surface of AD-BEC induces cellular signaling, promoting transmigration of monocytes from the apical to basolateral direction. We suggest that Abeta in the AD brain parenchyma or cerebrovasculature initiates cellular signaling that induces PBM to transmigrate across the BBB and accumulate in the brain.

RAGE is a multiligand receptor of the immunoglobulin superfamily: implications for homeostasis and chronic disease

Receptor for AGE (RAGE) is a member of the immunoglobulin superfamily that engages distinct classes of ligands. The biology of RAGE is driven by the settings in which these ligands accumulate, such as diabetes, inflammation, neurodegenerative disorders and tumors. In this review, we discuss the context of each of these classes of ligands, including advance glycation end-products, amyloid beta peptide and the family of beta sheet fibrils, S100/calgranulins and amphoterin. Implications for the role of these ligands interacting with RAGE in homeostasis and disease will be considered.

Alzheimer's disease: inside, outside, upside down

Neurotoxicity of beta-amyloid peptide (A beta) in Alzheimer's disease (AD) is usually thought to arise from the nonspecific effects of high concentrations of A beta on vulnerable neurons, resulting in membrane destabilization and increasing intracellular calcium concentration. This review advances the hypothesis that at early stages of AD, when A beta is present in lower amounts, its ability to perturb the function of cellular targets is mediated by specific cofactors present on the cell surface and intracellularly. Receptor for advanced glycation endproducts (RAGE) is a cell-surface receptor which binds A beta and amplifies its effects on cells in the nanomolar range. The intracellular enzyme A beta-binding alcohol dehydrogenase (ABAD) is likely to engage nascent A beta formed in the endoplasmic reticulum, and to mediate cell stress from this site. The analysis of A beta interaction with RAGE and ABAD, as well as other cofactors, provides insight into new mechanisms and, potentially, identifies therapeutic targets relevant to neuronal dysfunction in AD.

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.

Inflammatory repertoire of Alzheimer's disease and nondemented elderly microglia in vitro

We have previously developed and characterized isolated microglia and astrocyte cultures from rapid (<4 h) brain autopsies of Alzheimer's disease (AD) and nondemented elderly control (ND) patients. In the present study, we evaluate the inflammatory repertoire of AD and ND microglia cultured from white matter (corpus callosum) and gray matter (superior frontal gyrus) with respect to three major proinflammatory cytokines, three chemokines, a classical pathway complement component, a scavenger cell growth factor, and a reactive nitrogen intermediate. Significant, dose-dependent increases in the production of pro-interleukin-1beta (pro-IL-1beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory peptide-1alpha (MIP-1alpha), IL-8, and macrophage colony-stimulating factor (M-CSF) were observed after exposure to pre-aggregated amyloid beta peptide (1-42) (Abeta1-42). Across constitutive and Abeta-stimulated conditions, secretion of complement component C1q, a reactive nitrogen intermediate, and M-CSF was significantly higher in AD compared with ND microglia. Taken together with previous in situ hybridization findings, these results demonstrate unequivocally that elderly human microglia provide a brain endogenous source for a wide range of inflammatory mediators.

RAGE: a multiligand receptor contributing to the cellular response in diabetic vasculopathy and inflammation

RAGE is a multiligand member of the immunoglobulin superfamily of cell surface molecules whose properties extend the paradigm of ligand-receptor interactions. The receptor recognizes families of ligands with diverse structural features, such as advanced glycation endproducts (AGEs), amyloidogenic peptides/polypeptides, amphoterins, and S100/calgranulins rather than individual species. Engagement of RAGE by its ligands upregulates the receptor and initiates a cycle of sustained cellular perturbation; increased levels of RAGE on the cell surface make it an ideal target for subsequent ligand interactions and for propagating cellular dysfunction. At this time, the only means known to break this apparently vicious cycle appears to be blocking access to RAGE or removing the ligands. Taken together, these data suggest that RAGE has the potential to function as a progression factor in a range of disorders (AGEs are relevant to diabetes and other settings of oxidant stress, amyloidogenic peptides are relevant to amyloidoses, S100/calgranulins are relevant to inflammatory disorders, etc.) in which its ligands accumulate. The chronic juxtaposition of ligand and receptor triggers sustained cellular perturbation favoring mechanisms eventuating in tissue injury rather than those that would restore homeostasis.

The biology of the receptor for advanced glycation end products and its ligands

Receptor for advanced glycation end products (RAGE) is a multiligand member of the immunoglobulin superfamily of cell surface molecules whose repertoire of ligands includes advanced glycation end products (AGEs), amyloid fibrils, amphoterins and S100/calgranulins. The overlapping distribution of these ligands and cells overexpressing RAGE results in sustained receptor expression which is magnified via the apparent capacity of ligands to upregulate the receptor. We hypothesize that RAGE-ligand interaction is a propagation factor in a range of chronic disorders, based on the enhanced accumulation of the ligands in diseased tissues. For example, increased levels of AGEs in diabetes and renal insufficiency, amyloid fibrils in Alzheimer's disease brain, amphoterin in tumors and S100/calgranulins at sites of inflammation have been identified. The engagement of RAGE by its ligands can be considered the 'first hit' in a two-stage model, in which the second phase of cellular perturbation is mediated by superimposed accumulation of modified lipoproteins (in atherosclerosis), invading bacterial pathogens, ischemic stress and other factors. Taken together, these 'two hits' eventuate in a cellular response with a propensity towards tissue destruction rather than resolution of the offending pathogenic stimulus. Experimental data are cited regarding this hypothesis, though further studies will be required, especially with selective low molecular weight inhibitors of RAGE and RAGE knockout mice, to obtain additional proof in support of our concept.

Recognition of structurally diverse substrates by type II 3-hydroxyacyl-CoA dehydrogenase (HADH II)/amyloid-beta binding alcohol dehydrogenase (ABAD)

Human type II hydroxyacyl-CoA dehydrogenase/amyloid-beta binding alcohol dehydrogenase (HADH II/ABAD) is an oxidoreductase whose salient features include broad substrate specificity, encompassing 3-hydroxyacyl-CoA derivatives, hydroxysteroids, alcohols and beta-hydroxybutyrate, and the capacity to bind amyloid-beta peptide, leading to propagation of amyloid-induced cell stress. In this study, we examine the structure and enzymatic activity of the homologous rat HADH II/ABAD enzyme. We report the crystal structure of rat HADH II/ABAD as a binary complex with its NADH cofactor to 2.0 A resolution, as a ternary complex with NAD(+) and 3-ketobutyrate (acetoacetate) to 1.4 A resolution, and as a ternary complex with NADH and 17 beta-estradiol to 1.7 A resolution. This first crystal structure of an HADH II confirms these enzymes are closely related to the short-chain hydroxysteroid dehydrogenases and differ substantially from the classic, type I 3-hydroxyacyl-CoA dehydrogenases. Binding of the ketobutyrate substrate is accompanied by closure of the active site specificity loop, whereas the steroid substrate does not appear to require closure for binding. Despite the different chemical nature of the two bound substrates, the presentation of chemical groups within the active site of each complex is remarkably similar, allowing a general mechanism for catalytic activity to be proposed. There is a characteristic extension to the active site that is likely to accommodate the CoA moiety of 3-hydroxyacyl-CoA substrates. Rat HADH II/ABAD also binds amyloid-beta (1-40) peptide with a K(D) of 21 nM, which is similar to the interaction exhibited between this peptide and human HADH II/ABAD. These studies provide the first structural insights into HADH II/ABAD interaction with its substrates, and indicate the relevance of the rodent enzyme and associated rodent models for analysis of HADH II/ABAD's physiologic and pathophysiologic properties.

Expression of Egr-1 in late stage emphysema

The transcription factor early growth response (Egr)-1 is an immediate-early gene product rapidly and transiently expressed after acute tissue injury. In contrast, in this report we demonstrate that lung tissue from patients undergoing lung reduction surgery for advanced emphysema, without clinical or anatomical evidence of acute infection, displays a selective and apparently sustained increase in Egr-1 transcripts and antigen, compared with a broad survey of other genes, including the transcription factor Sp1, whose levels were not significantly altered. Enhanced Egr-1 expression was especially evident in smooth muscle cells of bronchial and vascular walls, in alveolar macrophages, and some vascular endothelium. Gel shift analysis with (32)P-labeled Egr probe showed a band with nuclear extracts from emphysematous lung which was supershifted with antibody to Egr-1. Egr-1 has the capacity to regulate genes relevant to the pathophysiology of emphysema, namely those related to extracellular matrix formation and remodeling, thrombogenesis, and those encoding cytokines/chemokines and growth factors. Thus, we propose that further analysis of Egr-1, which appears to be up-regulated in a sustained fashion in patients with late stage emphysema, may provide insights into the pathogenesis of this destructive pulmonary disease, as well as a new facet in the biology of Egr-1.

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.

Interaction of the receptor for advanced glycation end products (RAGE) with transthyretin triggers nuclear transcription factor kB (NF-kB) activation

Mutated transthyretin (TTR) fibrils are associated with the pathology of familial amyloidotic polyneuropathy (FAP), in which extracellular amyloid deposits lead to degeneration of cells and tissues, in particular neurons of the peripheral nerve. Here we present evidence that the receptor for advanced glycation end products (RAGE), previously associated with Alzheimer's disease, acts as a selective cell surface acceptor site for both soluble and fibrillar TTR. Immunohistochemical studies demonstrating increased expression of RAGE in FAP tissues suggested the relevance of this receptor to TTR-induced fibrillar pathology. In vitro studies using soluble RAGE showed saturable specific interaction with soluble and fibrillar TTR with a K(d) of approximately 120 nM. However, no binding was observed when soluble TTR was combined with retinol-binding protein, which represents the form in which TTR normally circulates in plasma. Specific binding of TTR to RAGE-transfected Chinese hamster ovary cells (which was completely blocked by anti-RAGE) was observed, confirming that RAGE could mediate TTR binding to cellular surfaces. RAGE-dependent activation of nuclear transcription factor kB (NF-kB) by TTR fibrils was shown in PC-12 cells stably transfected to overexpress the receptor. Furthermore, FAP nerves showed up-regulation of p50, one of the NF-kB subunits, when compared with age-matched controls. From these observations we predict that, in vivo, the presence of TTR fibrils associated with cellular surfaces of FAP patients, by contributing to NF-kB activation, leads to the pathogenesis of neurodegeneration. Further insights into the consequences of the interaction of fibrillar TTR with RAGE may therefore provide a better understanding of neurodegeneration associated with FAP.

Receptor-dependent cell stress and amyloid accumulation in systemic amyloidosis

Accumulation of fibrils composed of amyloid A in tissues resulting in displacement of normal structures and cellular dysfunction is the characteristic feature of systemic amyloidoses. Here we show that RAGE, a multiligand immunoglobulin superfamily cell surface molecule, is a receptor for the amyloidogenic form of serum amyloid A. Interactions between RAGE and amyloid A induced cellular perturbation. In a mouse model, amyloid A accumulation, evidence of cell stress and expression of RAGE were closely linked. Antagonizing RAGE suppressed cell stress and amyloid deposition in mouse spleens. These data indicate that RAGE is a potential target for inhibiting accumulation of amyloid A and for limiting cellular dysfunction induced by amyloid A.

Chronic aminoguanidine attenuates renal dysfunction and injury in aging rats

We have previously shown that aging is associated with increased lipid peroxidation, reductions in renal function, and increased glomerular sclerosis. The mechanism(s) responsible for these age-related changes are not clear. The purpose of the present studies was to determine if there was an increase in inducible nitric oxide synthase (iNOS) with aging, and if so, whether inhibition of iNOS would prevent aging injury by preventing free radical-mediated lipid peroxidation. iNOS protein expression in the kidney increased by approximately 90% by 24 months. Inhibition of iNOS by aminoguanidine (0.1% in drinking water) for 9 months, beginning at 13 months of age, reduced blood pressure, improved glomerular filtration rate by 70%, and renal plasma flow by 40%, whereas glomerular sclerosis was considerably reduced. Renal F2-isoprostanes and malondialdehyde levels, markers of oxidative stress and lipid peroxidation, were not reduced by aminoguanidine. Aminoguanidine also did not attenuate immunostaining for advanced glycosylation end products (AGE) in the kidneys. These findings suggest that aminoguanidine attenuates aging renal dysfunction by inhibiting a pathophysiologic function of iNOS that is independent of free radical-mediated lipid peroxidation or significant effects on AGE deposition.

Activation of receptor for advanced glycation end products: a mechanism for chronic vascular dysfunction in diabetic vasculopathy and atherosclerosis

Receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules and engages diverse ligands relevant to distinct pathological processes. One class of RAGE ligands includes glycoxidation products, termed advanced glycation end products, which occur in diabetes, at sites of oxidant stress in tissues, and in renal failure and amyloidoses. RAGE also functions as a signal transduction receptor for amyloid beta peptide, known to accumulate in Alzheimer disease in both affected brain parenchyma and cerebral vasculature. Interaction of RAGE with these ligands enhances receptor expression and initiates a positive feedback loop whereby receptor occupancy triggers increased RAGE expression, thereby perpetuating another wave of cellular activation. Sustained expression of RAGE by critical target cells, including endothelium, smooth muscle cells, mononuclear phagocytes, and neurons, in proximity to these ligands, sets the stage for chronic cellular activation and tissue damage. In a model of accelerated atherosclerosis associated with diabetes in genetically manipulated mice, blockade of cell surface RAGE by infusion of a soluble, truncated form of the receptor completely suppressed enhanced formation of vascular lesions. Amelioration of atherosclerosis in these diabetic/atherosclerotic animals by soluble RAGE occurred in the absence of changes in plasma lipids or glycemia, emphasizing the contribution of a lipid- and glycemia-independent mechanism(s) to atherogenesis, which we postulate to be interaction of RAGE with its ligands. Future studies using mice in which RAGE expression has been genetically manipulated and with selective low molecular weight RAGE inhibitors will be required to definitively assign a critical role for RAGE activation in diabetic vasculopathy. However, sustained receptor expression in a microenvironment with a plethora of ligand makes possible prolonged receptor stimulation, suggesting that interaction of cellular RAGE with its ligands could be a factor contributing to a range of important chronic disorders.

Role of ERAB/L-3-hydroxyacyl-coenzyme A dehydrogenase type II activity in Abeta-induced cytotoxicity

Endoplasmic reticulum-associated amyloid beta-peptide (Abeta)-binding protein (ERAB)/L-3-hydroxyacyl-CoA dehydrogenase type II (HADH II) is expressed at high levels in Alzheimer's disease (AD)-affected brain, binds Abeta, and contributes to Abeta-induced cytotoxicity. Purified recombinant ERAB/HADH II catalyzed the NADH-dependent reduction of S-acetoacetyl-CoA with a Km of approximately 68 microM and a Vmax of approximately 430 micromol/min/mg. The contribution of ERAB/HADH II enzymatic activity to Abeta-mediated cellular dysfunction was studied by site-directed mutagenesis in the catalytic domain (Y168G/K172G). Although COS cells cotransfected to overexpress wild-type ERAB/HADH II and variant beta-amyloid precursor protein (betaAPP(V717G)) showed DNA fragmentation, cotransfection with Y168G/K172G-altered ERAB and betaAPP(V717G) was without effect. We thus asked whether the enzyme might recognize alcohol substrates of which the aldehyde products could be cytotoxic; ERAB/HADH II catalyzed oxidation of a variety of simple alcohols (C2-C10) to their respective aldehydes in the presence of NAD+ and NAD-dependent oxidation of 17beta-estradiol. Addition of micromolar levels of synthetic Abeta(1-40) to purified ERAB/HADH II inhibited, in parallel, reduction of S-acetoacetyl-CoA (Ki approximately 1.6 microM), as well as oxidation of 17beta-estradiol (Ki approximately 3.2 microM) and (-)-2-octanol (Ki approximately 2.6 microM). Because micromolar levels of Abeta were required to inhibit ERAB/HADH II activity, whereas Abeta binding to ERAB/HADH II occurred at much lower concentrations (Km approximately 40-70 nM), the latter more closely simulating Abeta levels within cells, Abeta perturbation of ERAB/HADH II was likely to result from mechanisms other than the direct modulation of enzymatic activity. Cells cotransfected to overexpress ERAB/HADH II and betaAPP(V717G) generated malondialdehyde-protein and 4-hydroxynonenal-protein epitopes, which were detectable only at the lowest levels in cells overexpressing either ERAB/HADH II or betaAPP(V717G) alone. Generation of such toxic aldehydes was not observed in cells contransfected to overexpress Y168G/K172G-altered ERAB and betaAPP(V717G). We conclude that the generalized alcohol dehydrogenase activity of ERAB/HADH II is central to the cytotoxicity observed in an Abeta-rich environment.

Human blood-brain barrier receptors for Alzheimer's amyloid-beta 1- 40. Asymmetrical binding, endocytosis, and transcytosis at the apical side of brain microvascular endothelial cell monolayer

A soluble monomeric form of Alzheimer's amyloid-beta (1-40) peptide (sAbeta1-40) is present in the circulation and could contribute to neurotoxicity if it crosses the brain capillary endothelium, which comprises the blood-brain barrier (BBB) in vivo. This study characterizes endothelial binding and transcytosis of a synthetic peptide homologous to human sAbeta1-40 using an in vitro model of human BBB. 125I-sAbeta1-40 binding to the brain microvascular endothelial cell monolayer was time dependent, polarized to the apical side, and saturable with high- and low-affinity dissociation constants of 7.8+/-1.2 and 52.8+/-6.2 nM, respectively. Binding of 125I-sAbeta1-40 was inhibited by anti-RAGE (receptor for advanced glycation end products) antibody (63%) and by acetylated low density lipoproteins (33%). Consistent with these data, transfected cultured cells overexpressing RAGE or macrophage scavenger receptor (SR), type A, displayed binding and internalization of 125I-sAbeta1-40. The internalized peptide remains intact > 94%. Transcytosis of 125I-sAbeta1-40 was time and temperature dependent, asymmetrical from the apical to basolateral side, saturable with a Michaelis constant of 45+/-9 nM, and partially sensitive to RAGE blockade (36%) but not to SR blockade. We conclude that RAGE and SR mediate binding of sAbeta1-40 at the apical side of human BBB, and that RAGE is also involved in sAbeta1-40 transcytosis.

RAGE-Abeta interactions in the pathophysiology of Alzheimer's disease

RAGE is a cell surface molecule primarily identified for its capacity to bind advanced glycation end-products and amphoterin. Immunocytochemical studies demonstrated that in Alzheimer's Disease (AD) the expression of RAGE is elevated in neurons close to neuritic plaque beta-amyloid (Abeta) deposits and in the cells of Abeta containing vessels. Cross-linking of surface bound Abeta 1-40 to endothelial cells, yielded a band of 50 kDa identified as RAGE. Using the soluble extracellular domain of recombinant human RAGE, we found that Abeta binds to RAGE with a Kd = 57 +/- 14 nM, a value close to those found for mouse brain endothelial cells and rat cortical neurons. The interaction of Abeta with RAGE in neuronal, endothelial, and RAGE-transfected COS-1 cells induced oxidative stress, as assessed by the TBARS and MTT assays. ELISA demonstrated a 2.5 times increase of RAGE in AD over control brains. Activated microglia also showed elevated expression of RAGE. In the BV-2 microglial cell line, RAGE bound Abeta in dose dependent manner with a Kd of 25 +/- 9 nM. Soluble Abeta induced the migration of microglia along a concentration gradient, while immobilized Abeta arrested this migration. Abeta-RAGE interaction also activated NF-kappaB, resulting in neuronal up-regulation of macrophage-colony stimulating factor (M-CSF) which also induced microglial migration. Taken together, our data suggest that RAGE-Abeta interactions play an important role in the pathophysiology of Alzheimer's Disease.

Vitamin E ameliorates enhanced renal lipid peroxidation and accumulation of F2-isoprostanes in aging kidneys

Aging results in progressive glomerular sclerosis and reductions in glomerular filtration rate (GFR). Oxidative stress may be an important mechanism for the aging process, but to date the role of oxidative stress on renal aging has not been determined. The present study was performed to determine whether age-related alterations in renal hemodynamics and morphology were associated with oxidative stress and whether this could be attenuated by chronic administration of vitamin E. Rats, aged 13 mo, were given either control diet containing vitamin E 50 IU/kg (n = 6) or a high-vitamin E diet (5,000 IU/kg; n = 6) for 9 mo. Another group of rats (3-4 mo old; n = 7) served as young controls. Aging was accompanied by a 60% reduction in GFR, a threefold increase in renal F2 isoprostanes, newly discovered vasoconstrictive F2-like prostaglandins generated by free radical-mediated lipid peroxidation. Renal aging was also associated with an increase in oxidant-sensitive heme oxygenase, advanced glycosylation end products (AGEs), and the AGE receptor, RAGE. AGE-RAGE interaction has been shown to induce oxidative stress. With high-vitamin E diet, GFR was increased by 50%, F2 isoprostanes were suppressed, and expression of heme oxygenase and RAGE was attenuated. There was also a tendency for glomerular sclerosis to be attenuated. These data demonstrate that age-related decline in renal function is accompanied by oxidative stress and that administration of antioxidants, such as vitamin E, could attenuate the decline in renal function.

An intracellular protein that binds amyloid-beta peptide and mediates neurotoxicity in Alzheimer's disease

Amyloid-beta is a neurotoxic peptide which is implicated in the pathogenesis of Alzheimer's disease. It binds an intracellular polypeptide known as ERAB, thought to be a hydroxysteroid dehydrogenase enzyme, which is expressed in normal tissues, but is overexpressed in neurons affected in Alzheimer's disease. ERAB immunoprecipitates with amyloid-beta, and when cell cultures are exposed to amyloid-beta, ERAB inside the cell is rapidly redistributed to the plasma membrane. The toxic effect of amyloid-beta on these cells is prevented by blocking ERAB and is enhanced by overexpression of ERAB. By interacting with intracellular amyloid-beta, ERAB may therefore contribute to the neuronal dysfunction associated with Alzheimer's disease.

Monocytes and tissue factor promote thrombosis in a murine model of oxygen deprivation

Clinical conditions associated with local or systemic hypoxemia can lead to prothrombotic diatheses. This study was undertaken to establish a model of whole-animal hypoxia wherein oxygen deprivation by itself would be sufficient to trigger tissue thrombosis. Furthermore, this model was used to test the hypothesis that hypoxia-induced mononuclear phagocyte (MP) recruitment and tissue factor (TF) expression may trigger the local deposition of fibrin which occurs in response to oxygen deprivation. Using an environmental chamber in which inhaled oxygen tension was lowered to 6%, hypoxic induction of thrombosis was demonstrated in murine pulmonary vasculature by 8 h based upon: (a) immunohistologic evidence of fibrin formation in hypoxic lung tissue using an antifibrin antibody, confirmed by 22.5-nm strand periodicity by electron microscopy; (b) immunoblots revealing fibrin gamma-gamma chain dimers in lungs from hypoxic but not normoxic mice or hypoxic mice treated with hirudin; (c) accelerated deposition of 125I-fibrin/fibrinogen and 111In-labeled platelets in the lung tissue of hypoxic compared with normoxic animals; (d) reduction of tissue 125I-fibrin/fibrinogen accumulation in animals which had either been treated with hirudin or depleted of platelets before hypoxic exposure. Because immunohistochemical analysis of hypoxic pulmonary tissue revealed strong MP staining for TF, confirmed by increased TF RNA in hypoxic lungs, and because 111In-labeled murine MPs accumulated in hypoxic pulmonary tissue, we evaluated whether recruited MPs might be responsible for initiation of hypoxia-induced thrombosis. This hypothesis was supported by several lines of evidence: (a) MP depletion before hypoxia reduced thrombosis, as measured by reduced 125I-fibrin/fibrinogen deposition and reduced accumulation of cross-linked fibrin by immunoblot; (b) isolated murine MPs demonstrated increased TF immunostaining when exposed to hypoxia; and (c) administration of an anti-rabbit TF antibody that cross-reacts with murine TF decreased 125I-fibrin/fibrinogen accumulation and cross-linked fibrin accumulation in response to hypoxia in vivo. In summary, these studies using a novel in vivo model suggest that MP accumulation and TF expression may promote hypoxia-induced thrombosis.

Advanced glycation endproducts (AGEs) induce oxidant stress in the gingiva: a potential mechanism underlying accelerated periodontal disease associated with diabetes

We hypothesized that one mechanism underlying advanced periodontal disease in diabetes may involve oxidant stress in the gingiva, induced by the effects of Advanced Glycation Endproducts (AGEs), the irreversible products of non-enzymatic glycation and oxidation of proteins and lipids which accumulate in diabetic plasma and tissue. Infusion of AGE albumin, a prototypic ligand, into mice resulted in increased generation of thiobarbituric acid reactive substances (TBARS) compared with infusion of non-glycated albumin in the gingiva, as well as in the lung, kidney and brain. Pretreatment of the animals with the antioxidants probucol or N-acetylcysteine (NAC) prevented the generation of TBARS in the gingiva. Affinity-purified antibody to AGEs demonstrated increased immunoreactivity for AGEs in the vasculature and connective tissues of the gingiva in streptozotocin-induced diabetic mice compared to non-diabetic controls. Increased immunoreactivity for AGEs was also demonstrated in the gingiva of diabetic humans compared with non-diabetic individuals via immunohistochemistry and ELISA. Consistent with these data, immunohistochemistry for heme oxygenase-1, a marker of enhanced oxidant stress, was increased in the gingival vasculature of diabetic mice and humans compared with non-diabetic controls. These data suggest that AGEs present in diabetic gingiva may be associated with a state of enhanced oxidant stress, a potential mechanism for accelerated tissue injury.

The receptor for advanced glycation end products (RAGE) is a central mediator of the interaction of AGE-beta2microglobulin with human mononuclear phagocytes via an oxidant-sensitive pathway. Implications for the pathogenesis of dialysis-related amyloidosis

An important component of amyloid fibrils in dialysis-related amyloidosis is a form of beta2microglobulin modified with advanced glycation end products (AGEs) of the Maillard reaction, known as AGE-beta2M. We demonstrate here that the interaction of AGE-beta2M with mononuclear phagocytes (MPs), cells important in the pathogenesis of the inflammatory arthropathy of dialysis-related amyloidosis, is mediated by the receptor for AGEs, or RAGE. 125I-AGE-beta2M bound to immobilized RAGE or to MPs in a specific, dose-dependent manner (Kd approximately 53.5 and approximately 81.6 nM, respectively), a process inhibited in the presence of RAGE blockade. AGE-beta2M-mediated monocyte chemotaxis was prevented by excess sRAGE or anti-RAGE IgG. Induction of tumor necrosis factor-alpha (TNF) expression by MPs exposed to AGE-beta2M resulted from engagement of RAGE, as appearances of TNF transcripts and TNF antigen release into culture supernatants were prevented by addition of sRAGE, a process mediated, at least in part, by oxidant stress. AGE-beta2M reduced cytochrome c and the elaboration of TNF by MPs was inhibited by N-acetylcysteine. Consistent with these data, immunohistochemical studies of AGE-laden amyloid deposits of a long-term hemodialysis patient revealed positive staining for RAGE in the MPs infiltrating these lesions. These data indicate that RAGE is a central binding site for AGEs formed in vivo and suggest that AGE-beta2M-MP-RAGE interaction likely contributes to the initiation of an inflammatory response in amyloid deposits of long-term hemodialysis patients, a process which may ultimately lead to bone and joint destruction.

RAGE and amyloid-beta peptide neurotoxicity in Alzheimer's disease

Amyloid-beta peptide is central to the pathology of Alzheimer's disease, because it is neurotoxic--directly by inducing oxidant stress, and indirectly by activating microglia. A specific cell-surface acceptor site that could focus its effects on target cells has been postulated but not identified. Here we present evidence that the 'receptor for advanced glycation end products' (RAGE) is such a receptor, and that it mediates effects of the peptide on neurons and microglia. Increased expressing of RAGE in Alzheimer's disease brain indicates that it is relevant to the pathogenesis of neuronal dysfunction and death.

RAGE: a novel cellular receptor for advanced glycation end products

Exposure of proteins to reducing sugars results in nonenzymatic glycation with the ultimate formation of advanced glycation end products (AGEs). One means through which AGEs modulate cellular functions is through binding to specific cell surface acceptor molecules. The receptor for AGEs (RAGE) is such a receptor and is a newly identified member of the immunoglobulin superfamily expressed on endothelial cells (ECs), mononuclear phagocytes (MPs), and vascular smooth muscle cells (SMCs) in both vivo and in vitro. Binding of AGEs to RAGE results in induction of cellular oxidant stress, as exemplified by the generation of thiobarbituric acid-reactive substances, expression of heme oxygenase type I, and activation of the transcription factor NF-kB, with consequences for a range of cellular functions. AGEs on the surface of diabetic red cells enhance binding to endothelial RAGE and result in enhanced oxidant stress in the vessel wall. By using reagents to selectively block access to RAGE, the role of this receptor in AGE-mediated perturbation of cellular properties can be dissected in detail.

The receptor for advanced glycation end-products has a central role in mediating the effects of advanced glycation end-products on the development of vascular disease in diabetes mellitus

Proteins or lipids exposed to aldose sugars undergo initial and ultimately irreversible modification resulting in the formation of so-called advanced glycation end-products (AGEs). AGEs are postulated to be especially important in the setting of diabetes mellitus due to hyperglycaemia characteristic of this disorder. Our work has demonstrated that one of the principal means by which AGEs interact with the vascular wall is by interaction with their cellular receptor, the receptor for advanced glycation end-products (RAGE), which is present on the surface of endothelial cells, smooth muscle cells, mesangial cells, mononuclear phagocytes and certain neurons. AGEs interact with RAGE, resulting in the induction of monocyte chemotaxis as well as oxidant stress. One of the consequences of AGE-RAGE-induced cellular oxidant stress is the enhanced expression of vascular cell adhesion molecule-1 on the endothelial surface, a critical consequence of which is the attraction of mononuclear phagocytes into the vessel wall. In both cases, the pro-inflammatory effects of AGEs may be inhibited in the presence of RAGE blockade, using either anti-RAGE F(ab')2 or soluble RAGE, the extracellular domain of the molecule. These data suggest that inhibition of RAGE may interfere with monocyte chemotaxis and attraction into the vessel wall where AGEs deposit/form, suggesting the potential of this intervention to interfere with a critical step in the development of vascular disease, especially in patients with diabetes.

Cerebral protection in homozygous null ICAM-1 mice after middle cerebral artery occlusion. Role of neutrophil adhesion in the pathogenesis of stroke

Acute neutrophil (PMN) recruitment to postischemic cardiac or pulmonary tissue has deleterious effects in the early reperfusion period, but the mechanisms and effects of neutrophil influx in the pathogenesis of evolving stroke remain controversial. To investigate whether PMNs contribute to adverse neurologic sequelae and mortality after stroke, and to study the potential role of the leukocyte adhesion molecule intercellular adhesion molecule-1 (ICAM-1) in the pathogenesis of stroke, we used a murine model of transient focal cerebral ischemia consisting of intraluminal middle cerebral artery occlusion for 45 min followed by 22 h of reperfusion. PMN accumulation, monitored by deposition of 111In-labeled PMNs in postischemic cerebral tissue, was increased 2.5-fold in the ipsilateral (infarcted) hemisphere compared with the contralateral (noninfarcted) hemisphere (P < 0.01). Mice immunodepleted of neutrophils before surgery demonstrated a 3.0-fold reduction in infarct volumes (P < 0.001), based on triphenyltetrazolium chloride staining of serial cerebral sections, improved ipsilateral cortical cerebral blood flow (measured by laser Doppler), and reduced neurological deficit compared with controls. In wild-type mice subjected to 45 min of ischemia followed by 22 h of reperfusion, ICAM-1 mRNA was increased in the ipsilateral hemisphere, with immunohistochemistry localizing increased ICAM-1 expression on cerebral microvascular endothelium. The role of ICAM-1 expression in stroke was investigated in homozygous null ICAM-1 mice (ICAM-1 -/-) in comparison with wild-type controls (ICAM-1 +/+). ICAM-1 -/- mice demonstrated a 3.7-fold reduction in infarct volume (P < 0.005), a 35% increase in survival (P < 0.05), and reduced neurologic deficit compared with ICAM-1 +/+ controls. Cerebral blood flow to the infarcted hemisphere was 3.1-fold greater in ICAM-1 -/- mice compared with ICAM-1 +/+ controls (P < 0.01), suggesting an important role for ICAM-1 in the genesis of postischemic cerebral no-reflow. Because PMN-depleted and ICAM-1-deficient mice are relatively resistant to cerebral ischemia-reperfusion injury, these studies suggest an important role for ICAM-1-mediated PMN adhesion in the pathophysiology of evolving stroke.

Advanced glycation endproducts interacting with their endothelial receptor induce expression of vascular cell adhesion molecule-1 (VCAM-1) in cultured human endothelial cells and in mice. A potential mechanism for the accelerated vasculopathy of diabetes

Vascular cell adhesion molecule-1 (VCAM-1), an inducible cell-cell recognition protein on the endothelial cell surface (EC), has been associated with early stages of atherosclerosis. In view of the accelerated vascular disease observed in patients with diabetes, and the enhanced expression of VCAM-1 in diabetic rabbits, we examined whether irreversible advanced glycation endproducts (AGEs), could mediate VCAM-1 expression by interacting with their endothelial cell receptor (receptor for AGE, RAGE). Exposure of cultured human ECs to AGEs induced expression of VCAM-1, increased adhesivity of the monolayer for Molt-4 cells, and was associated with increased levels of VCAM-1 transcripts. The inhibitory effect of anti-RAGE IgG, a truncated form of the receptor (soluble RAGE) or N-acetylcysteine on VCAM-1 expression indicated that AGE-RAGE-induced oxidant stress was central to VCAM-1 induction. Electrophoretic mobility shift assays on nuclear extracts from AGE-treated ECs showed induction of specific DNA binding activity for NF-kB in the VCAM-1 promoter, which was blocked by anti-RAGE IgG or N-acetylcysteine. Soluble VCAM-1 antigen was elevated in human diabetic plasma. These data are consistent with the hypothesis that AGE-RAGE interaction induces expression of VCAM-1 which can prime diabetic vasculature for enhanced interaction with circulating monocytes.

Non-enzymatically glycated tau in Alzheimer's disease induces neuronal oxidant stress resulting in cytokine gene expression and release of amyloid beta-peptide

Paired helical filament (PHF) tau is the principal component of neurofibrillary tangles, a characteristic feature of the neurodegenerative pathology in Alzheimer's disease (AD). Post-translational modification of tau, especially phosphorylation, has been considered a major factor in aggregation and diminished microtubule interactions of PHF-tau. Recently, it has been recognized that PHF-tau is also subject to non-enzymatic glycation, with formation of advanced glycation end products (AGEs). We now show that as a consequence of glycation, PHF-tau from AD and AGE-tau generate oxygen free radicals, thereby activating transcription via nuclear factor-kappa B, increasing amyloid beta-protein precursor and release of approximately 4 kD amyloid beta-peptides. These data provide insight into how PHF-tau disturbs neuronal function, and add to a growing body of evidence that oxidant stress contributes to the pathogenesis of AD.

Alzheimer neurofibrillary lesions: molecular nature and potential roles of different components

Neurofibrillary lesions found in Alzheimer disease (AD) are known to react with antibodies raised against different molecules. At least 20 components have been detected in neurofibrillary tangles. These components can be roughly categorized into five groups, which include structural proteins, kinases and other cytosolic enzymes, stress-related molecules, amyloid and amyloid binding proteins, and others. Among them, an abnormal form of microtubule associated protein tau, PHF-tau, is a major component of Alzheimer NFT. Kinases associated with NFT, especially those belonging to the family of proline-directed Ser/Thr kinases, are considered to be important for PHF-tau hyperphosphorylation. A potentially significant kinase is a Cdc2-related kinase, which is associated tightly with paired helical filaments, has a molecular weight of 33kDa and is different from other known Cdc2-related kinases. The possibility that some of the NFT-associated elements may play an active role in the pathogenesis of Alzheimer's disease was supported by recent studies, in which advanced glycated products and markers of oxidant stress were located in NFT. In addition, PHF-tau was found to be glycated, and in vitro glycated tau was capable of inducing oxidant stress. Further characterization of different components of NFT by biochemical and other approaches will be important for understanding the mechanisms involved in the supramolecular aggregation of PHF within NFT.

Hypoxia/reoxygenation-mediated induction of astrocyte interleukin 6: a paracrine mechanism potentially enhancing neuron survival

To elucidate mechanisms underlying neuroprotective properties of astrocytes in brain ischemia, production of neurotrophic mediators was studied in astrocytes exposed to hypoxia/reoxygenation (H/R). Rat astrocytes subjected to H/R released increased amounts of interleukin (IL) 6 in a time-dependent manner, whereas levels of tumor necrosis factor and IL-1 remained undetectable. IL-6 transcripts were induced in hypoxia and the early phase of reoxygenation, whereas synthesis and release of IL-6 antigen/activity occurred during reoxygenation. Elevated levels of IL-6 mRNA were due, at least in part, to increased transcription, as shown by nuclear runoff analysis. The mechanism stimulating synthesis and release of IL-6 antigen by astrocytes was probably production of reactive oxygen intermediates (ROIs), which occurred within 15-20 minutes after placing hypoxia cultures back into normoxia, as the inhibitor diphenyl iodonium inhibited the burst of ROIs and subsequent IL-6 generation (blockade of nitric oxide formation had no effect on ROI generation or IL-6 production). Enhanced IL-6 generation was also observed in human astrocytoma cultures exposed to H/R. Survival of differentiated PC12 cells exposed to H/R was potentiated by conditioned medium from H/R astrocytes, an effect blocked by neutralizing anti-IL-6 antibody. In a gerbil model of brain ischemia, IL-6 activity was lower in the hippocampus, an area sensitive to ischemia, compared with IL-6 activity in the cortex, an area more resistant to ischemia. IL-6 antigen, demonstrated immunohistochemically, was increased in astrocytes from ischemic regions of gerbil brain. These data suggest that H/R enhances transcription of IL-6, resulting in increased translation and release of IL-6 antigen after the burst of ROI generated early during reoxygenation. Release of IL-6 from astrocytes could exert a paracrine neurotrophic effect in brain ischemia.

Cellular receptors for advanced glycation end products. Implications for induction of oxidant stress and cellular dysfunction in the pathogenesis of vascular lesions

Advanced glycation end products (AGEs) form by the interaction of aldoses with proteins and the subsequent molecular rearrangements of the covalently linked sugars, eventuating in a diverse group of fluorescent compounds of yellow-brown color. This heterogeneous class of nonenzymatically glycated proteins or lipids is found in the plasma and accumulates in the vessel wall and tissues even in normal aging. As a consequence of hyperglycemia, AGE formation and deposition are much enhanced in diabetes, in which their presence has been linked to secondary complications, especially microvascular disease. This review summarizes the cellular interactions of AGEs and describes the central role of a novel receptor for AGE (RAGE). RAGE, an immunoglobulin superfamily member, mediates the binding of AGEs to endothelial cells and mononuclear phagocytes, interacts with a lactoferrin-like polypeptide that also binds AGEs, and appears to activate intracellular signal transduction mechanisms consequent to its interaction with the glycated ligand. RAGE is expressed by ECs, mononuclear phagocytes, smooth muscle cells, mesangial cells, and neurons, indicating a potential role in the regulation of their properties in homeostasis and/or their dysfunction in the development of diabetic complications. Since AGEs have been shown to generate reactive oxygen intermediates, tethering of AGEs to the cell surface by their receptors focuses oxidant stress on cellular targets, resulting in changes in gene expression and the cellular phenotype. The discovery of RAGE and development of reagents to block its interaction with AGEs should provide insights into the role of this ligand-receptor interaction in the pathogenesis of diabetic complications and, potentially, atherosclerosis.

Receptor for advanced glycation end products (AGEs) has a central role in vessel wall interactions and gene activation in response to circulating AGE proteins

The extended interaction of aldoses with proteins or lipids results in nonenzymatic glycation and oxidation, ultimately forming AGEs, the presence of which in the plasma and vessel wall is associated with diabetic vascular complications. We show here that AGE albumin in the intravascular space interacts with the vessel wall via binding to an integral membrane protein, receptor for AGE (RAGE), a member of the immunoglobulin superfamily, resulting in clearance from the plasma and induction of interleukin 6 mRNA. Intravenously infused 125I-AGE albumin showed a rapid phase of plasma clearance with deposition in several organs. Rapid removal of 125I-AGE albumin from the plasma was prevented by administration of a soluble, truncated form of RAGE, which blocked binding of 125I-labeled AGE albumin to cultured endothelial cells and mononuclear phagocytes, as well as by pretreatment with anti-RAGE IgG. Ultrastructural studies with AGE albumin-colloidal gold conjugates perfused in situ showed that in murine coronary vasculature this probe was taken up by endothelial plasmalemmal vesicles followed by transport either to the abluminal surface or by accumulation in intracellular vesicular structures reminiscent of endosomes and lysosomes. Consequences of AGE-RAGE interaction included induction of interleukin 6 mRNA expression in mice. These data indicate that RAGE mediates the interaction of AGEs with the vessel wall, both for removal of these glycated proteins from the plasma and for changes in gene expression.

Advanced glycation end products (AGEs) on the surface of diabetic erythrocytes bind to the vessel wall via a specific receptor inducing oxidant stress in the vasculature: a link between surface-associated AGEs and diabetic complications

Vascular complications are an important cause of morbidity and mortality in patients with diabetes. The extent of vascular complications has been linked statistically to enhanced adherence of diabetic erythrocytes to endothelial cells (ECs) and to the accumulation of a class of glycated proteins termed advanced glycation end products (AGEs). We hypothesized that formation of AGEs on the surface of diabetic erythrocytes could mediate their interaction with ECs leading to binding and induction of vascular dysfunction. Enhanced binding of diabetic erythrocytes to ECs was blocked by preincubation of erythrocytes with anti-AGE IgG or preincubation of ECs with antibodies to the receptor for AGE (RAGE). Immunoblotting of cultured human ECs and immunostaining of normal/diabetic human tissue confirmed the presence of RAGE in the vessel wall. Binding of diabetic erythrocytes to endothelium generated an oxidant stress, as measured by production of thiobarbituric acid-reactive substances (TBARS) and activation of the transcription factor NF-kappa B, both of which were blocked by probucol or anti-RAGE IgG. Erythrocytes from diabetic rats infused into normal rats had an accelerated, early phase of clearance that was prevented, in part, by antibody to RAGE. Liver tissue from rats infused with diabetic erythrocytes showed elevated levels of TBARS, which was prevented by pretreatment with anti-RAGE IgG or probucol. Thus, erythrocyte surface AGEs can function as ligands that interact with RAGE on endothelium. The extensive contact of diabetic erythrocytes bearing surface-associated AGEs with vessel wall RAGE could be important in the development of vascular complications.

Glycated tau protein in Alzheimer disease: a mechanism for induction of oxidant stress

The stability of proteins that constitute the neurofibrillary tangles and senile plaques of Alzheimer disease suggests that they would be ideal substrates for nonenzymatic glycation, a process that occurs over long times, even at normal levels of glucose, ultimately resulting in the formation of advanced glycation end products (AGEs). AGE-modified proteins aggregate, and they generate reactive oxygen intermediates. Using monospecific antibody to AGEs, we have colocalized these AGEs with paired helical filament tau in neurofibrillary tangles in sporadic Alzheimer disease. Such neurons also exhibited evidence of oxidant stress: induction of malondialdehyde epitopes and heme oxygenase 1 antigen. AGE-recombinant tau generated reactive oxygen intermediates and, when introduced into the cytoplasm of SH-SY5Y neuroblastoma cells, induced oxidant stress. We propose that in Alzheimer disease, AGEs in paired helical filament tau can induce oxidant stress, thereby promoting neuronal dysfunction.

Tumor necrosis factor-alpha production in human head and neck squamous cell carcinoma

Recent studies suggest that tumor necrosis factor-alpha (TNF-alpha), a pleiotropic cytokine, is responsible for some of the systemic and local effects, including tumor-associated cachexia and neoplastic bone destruction, seen in patients with cancer. This study was undertaken to determine if TNF-alpha is produced by human squamous cell carcinoma of the head and neck, and, if so, to determine its source and cellular distribution. Tumor specimens from nine patients with squamous cell carcinoma of the head and neck region were immunohistochemically examined for the presence of TNF-alpha. TNF-alpha was localized with antibody to human TNF-alpha by the immunoperoxidase method to the tumor and vessel endothelial cells in all nine specimens. By Western blot analysis, two protein bands recognized by anti-human TNF-alpha antibody in the soluble proteins of the tumor specimens were identified. These proteins--25 KD and 17 KD--represent the precursor and mature forms of TNF-alpha. To verify squamous cell carcinoma production of TNF-alpha, a cell culture of human head and neck squamous carcinoma was examined. The 25 KD immunoreactive protein, the TNF-alpha precursor, was found in extracts from this culture by Western blot analysis. These findings suggest that tumor cells are able to produce TNF-alpha; this production may explain some of the systemic and local effects seen in patients with squamous cell carcinoma of the head and neck.

Heme oxygenase-1 is associated with the neurofibrillary pathology of Alzheimer's disease

Heme oxygenase-1 is an important enzyme that degrades heme, a pro-oxidant, leading to the formation of antioxidant molecules. In this study we demonstrate by immunocytochemistry close association of heme oxygenase-1 with Alzheimer neurofibrillary pathology and with the neurofibrillary tangles found in progressive supranuclear palsy and subacute sclerosing panencephalitis. In Alzheimer's disease, using two different rabbit antisera against heme oxygenase-1 protein, we localized, using immunocytochemical methods, heme oxygenase-1 to neurofibrillary tangles, senile plaque neurites, granulovacuolar degeneration, and neuropil threads. Only light background staining was seen in young controls and sporadic lesion-related immunoreactivity in age-matched controls. The increase in heme oxygenase-1 protein in association with the neurofibrillary pathology of Alzheimer's disease and other diseases characterized by neurofibrillary tangles supports the notion that the generation of free radicals and oxidative stress plays a role in the pathogenesis of neurofibrillary pathology.

Advanced Maillard reaction end products are associated with Alzheimer disease pathology

During aging long-lived proteins accumulate specific post-translational modifications. One family of modifications, termed Maillard reaction products, are initiated by the condensation between amino groups of proteins and reducing sugars. Protein modification by the Maillard reaction is associated with crosslink formation, decreased protein solubility, and increased protease resistance. Here, we present evidence that the characteristic pathological structures associated with Alzheimer disease contain modifications typical of advanced Maillard reaction end products. Specifically, antibodies against two Maillard end products, pyrraline and pentosidine, immunocytochemically label neurofibrillary tangles and senile plaques in brain tissue from patients with Alzheimer disease. In contrast, little or no staining is observed in apparently healthy neurons of the same brain. The Maillard-reaction-related modifications described herein could account for the biochemical and insolubility properties of the lesions of Alzheimer disease through the formation of protein crosslinks.

Hypoxic induction of interleukin-8 gene expression in human endothelial cells

Because leukocyte-mediated tissue damage is an important component of the pathologic picture in ischemia/reperfusion, we have sought mechanisms by which PMNs are directed into hypoxic tissue. Incubation of human endothelial cells (ECs) in hypoxia, PO2 approximately 14-18 Torr, led to time-dependent release of IL-8 antigen into the conditioned medium; this was accompanied by increased chemotactic activity for PMNs, blocked by antibody to IL-8. Production of IL-8 by hypoxic ECs occurred concomitantly with both increased levels of IL-8 mRNA, based on polymerase chain reaction analysis, and increased IL-8 transcription, based on nuclear run-on assays. Northern analysis of mRNA from hypoxic ECs also demonstrated increased levels of mRNA for macrophage chemotactic protein-1, another member of the chemokine superfamily of proinflammatory cytokines. IL-8 gene induction was associated with the presence of increased binding activity in nuclear extracts from hypoxic ECs for the NF-kB site. Studies with human umbilical vein segments exposed to hypoxia also demonstrated increased elaboration of IL-8 antigen compared with normoxic controls. In mice exposed to hypoxia (PO2 approximately 30-40 Torr), there was increased pulmonary leukostasis, as evidenced by increased myeloperoxidase activity in tissue homogenates. In parallel, increased levels of transcripts for IP-10, a murine homologue in the chemokine family related to IL-8, were observed in hypoxic lung tissue. Taken together, these data suggest that hypoxia constitutes a stimulus for leukocyte chemotaxis and tissue leukostasis.

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

Attack by reactive oxygen intermediates, common to many kinds of cell/tissue injury, has been implicated in the development of diabetic and other vascular diseases. Such oxygen-free radicals can be generated by advanced glycation end products (AGEs), which are nonenzymatically glycated and oxidized proteins. Since cellular interactions of AGEs are mediated by specific cellular binding proteins, receptor for AGE (RAGE) and the lactoferrin-like polypeptide (LF-L), we tested the hypothesis that AGE ligands tethered to the complex of RAGE and LF-L could induce oxidant stress. AGE albumin or AGEs immunoisolated from diabetic plasma resulted in induction of endothelial cell (EC) oxidant stress, including the generation of thiobarbituric acid reactive substances (TBARS) and resulted in the activation of NF-kappa B, each of which was blocked by antibodies to AGE receptor polypeptides and by antioxidants. Infusion of AGE albumin into normal animals led to the appearance of malondialdehyde determinants in the vessel wall and increased TBARS in the tissues, activation of NF-kappa B, and induction of heme oxygenase mRNA. AGE-induced oxidant stress was inhibited by pretreatment of animals with either antibodies to the AGE receptor/binding proteins or antioxidants. These data indicate that interaction of AGEs with cellular targets, such as ECs, leads to oxidant stress resulting in changes in gene expression and other cellular properties, potentially contributing to the development of vascular lesions. Further studies will be required to dissect whether oxidant stress occurs on the cell surface or at an intracellular locus.