A perspective on the Maillard reaction and the analysis of protein glycation by mass spectrometry: probing the pathogenesis of chronic disease

Quantitative analysis of glycation patterns in human serum albumin using 16O/18O-labeling and MALDI-TOF MS

BACKGROUND

The glycation of human serum albumin (HSA) during diabetes can affect the ability of this protein to bind drugs and small solutes in blood. This study describes the use of (16)O/(18)O-labeling and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to compare the levels of modification that occur throughout HSA under various glycation conditions in vitro. These quantitative studies build on a recent report that has identified the early and advanced glycation products that are formed on such samples of HSA.

METHODS

Glycated HSA samples were prepared by incubating 42 g/l HSA with 0 to 15 mmol/l glucose at pH 7.4 and 37°C for up to 5 weeks. A control HSA sample was digested in (16)O-enriched water and glycated HSA samples were digested in the presence of (18)O-enriched water. These 2 types of samples were then mixed and the amounts of (16)O- vs. (18)O-labeled peptides were measured to determine the levels of modification that were occurring throughout HSA.

RESULTS

The largest levels of modification occurred in residues 101-119, 1-10 or 42-51, 87-100, 360-372, 521-531, and 275-286 of HSA after 2 weeks of glycation, and in residues 21-41, 1-10 or 42-51, 521-531, 82-93, and 146-160 after 5 weeks of glycation. Some of these regions contained the N-terminus, K199, K439, and K525, which have been previously identified as major glycation sites on HSA. The glycation pattern of HSA was dominated by early glycation products (e.g., fructosyl-lysine) after a reaction period of 2 weeks for mildly glycated HSA, while advanced glycation end products became more prominent at longer reaction times.

CONCLUSIONS

The time course of the observed modifications indicated that the pattern of glycation products changed as HSA was incubated over longer periods of time with glucose. Several regions found to have significant levels of modification were at or near the major drug binding regions on HSA. These results explain why the interaction of some drugs with HSA has been observed to vary with the level of glycation for this protein.

Oxidative stress induced carbonylation in human plasma

The focus of this study was on the assessment of technology that might be of clinical utility in identification, quantification, characterization of carbonylation in human plasma proteins. Carbonylation is widely associated with oxidative stress diseases. Breast cancer patient samples were chosen as a stress positive case based on the fact that oxidative stress has been reported to be elevated in this disease. Measurements of 8-isoprostane in plasma confirmed that breast cancer patients in this study were indeed experiencing significant oxidative stress. Carbonyl groups in proteins from freshly drawn blood were derivatized with biotin hydrazide after which the samples were dialyzed and the biotinylated proteins subsequently selected, digested and labeled with iTRAQ™ heavy isotope coding reagent(s). Four hundred sixty proteins were identified and quantified, 95 of which changed 1.5 fold or more in concentration. Beyond confirming the utility of the analytical method, association of protein carbonylation was examined as well. Nearly one fourth of the selected proteins were of cytoplasmic, nuclear, or membrane origin. Analysis of the data by unbiased knowledge assembly methods indicated the most likely disease associated with the proteins was breast neoplasm. Pathway analysis showed the proteins which changed in carbonylation were strongly associated with Brca1, the breast cancer type-1 susceptibility protein. Pathway analysis indicated the major molecular functions of these proteins are defense, immunity and nucleic acid binding.

Comprehensive identification of glycated peptides and their glycation motifs in plasma and erythrocytes of control and diabetic subjects

Nonenzymatic glycation of proteins sets the stage for formation of advanced glycation end-products and development of chronic complications of diabetes. In this report, we extended our previous methods on proteomics analysis of glycated proteins to comprehensively identify glycated proteins in control and diabetic human plasma and erythrocytes. Using immunodepletion, enrichment, and fractionation strategies, we identified 7749 unique glycated peptides, corresponding to 3742 unique glycated proteins. Semiquantitative comparisons showed that glycation levels of a number of proteins were significantly increased in diabetes and that erythrocyte proteins were more extensively glycated than plasma proteins. A glycation motif analysis revealed that some amino acids were favored more than others in the protein primary structures in the vicinity of the glycation sites in both sample types. The glycated peptides and corresponding proteins reported here provide a foundation for potential identification of novel markers for diabetes, hyperglycemia, and diabetic complications in future studies.

AGE restriction in diabetes mellitus: a paradigm shift

Persistently elevated oxidative stress and inflammation precede or occur during the development of type 1 or type 2 diabetes mellitus and precipitate devastating complications. Given the rapidly increasing incidence of diabetes mellitus and obesity in the space of a few decades, new genetic mutations are unlikely to be the cause, instead pointing to environmental initiators. A hallmark of contemporary culture is a preference for thermally processed foods, replete with pro-oxidant advanced glycation endproducts (AGEs). These molecules are appetite-increasing and, thus, efficient enhancers of overnutrition (which promotes obesity) and oxidant overload (which promotes inflammation). Studies of genetic and nongenetic animal models of diabetes mellitus suggest that suppression of host defenses, under sustained pressure from food-derived AGEs, may potentially shift homeostasis towards a higher basal level of oxidative stress, inflammation and injury of both insulin-producing and insulin-responsive cells. This sequence promotes both types of diabetes mellitus. Reducing basal oxidative stress by AGE restriction in mice, without energy or nutrient change, reinstates host defenses, alleviates inflammation, prevents diabetes mellitus, vascular and renal complications and extends normal lifespan. Studies in healthy humans and in those with diabetes mellitus show that consumption of high amounts of food-related AGEs is a determinant of insulin resistance and inflammation and that AGE restriction improves both. This Review focuses on AGEs as novel initiators of oxidative stress that precedes, rather than results from, diabetes mellitus. Therapeutic gains from AGE restriction constitute a paradigm shift.

Comparison of modification sites formed on human serum albumin at various stages of glycation

BACKGROUND

Many of the complications encountered during diabetes can be linked to the non-enzymatic glycation of proteins, including human serum albumin (HSA). However, there is little information regarding how the glycation pattern of HSA changes as the total extent of glycation is varied. The goal of this study was to identify and conduct a semi-quantitative comparison of the glycation products on HSA that are produced in the presence of various levels of glycation.

METHODS

Three glycated HSA samples were prepared in vitro by incubating physiological concentrations of HSA with 15 mmol/l glucose for 2 or 5 weeks, or with 30 mmol/l glucose for 4 weeks. These samples were then digested and examined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the glycation products that were formed.

RESULTS

It was found that the glycation pattern of HSA changed with its overall extent of total glycation. Many modifications including previously-reported primary glycation sites (e.g., K199, K281, and the N-terminus) were consistently found in the tested samples. Lysines 199 and 281, as well as arginine 428, contained the most consistently identified and abundant glycation products. Lysines 93, 276, 286, 414, 439, and 524/525, as well as the N-terminus and arginines 98, 197, and 521, were also found to be modified at various degrees of HSA glycation.

CONCLUSIONS

The glycation pattern of HSA was found to vary with different levels of total glycation and included modifications at the 2 major drug binding sites on this protein. This result suggests that different modified forms of HSA, both in terms of the total extent of glycation and glycation pattern, may be found at various stages of diabetes. The clinical implication of these results is that the binding of HSA to some drug may be altered at various stages of diabetes as the extent of glycation and types of modifications in this protein are varied.

In vitro Antioxidant Activities of Maillard Reaction Products Produced in the Steaming Process of Polygonum multiflorum Root

The root of Polygonum multiflorum Thunb. (Heshouwu in Chinese) is one of the most popular herbs used in traditional Chinese medicine (TCM). However, after steam processing (Zhi-heshouwu in Chinese), the root is known to have different properties and medicinal values compared with Heshouwu. Eleven volatile Maillard reaction products were identified in the extract of Zhi-heshouwu, but not in that of Heshouwu. The new products were four furanones, two furans, two nitrogen compounds, one pyran, one alcohol and one sulfur compound. The antioxidant activities were compared between the extracts from Zhi-heshouwu and Heshouwu. The results showed that the extract from Zhi-heshouwu presented a higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity than the extract from Heshouwu, with IC50 values of 0.43 mg/mL and 2.9 mg/mL, respectively ( p<0.05). The hydroxyl radical scavenging activities of the two were similar (IC50 0.98 mg/mL and 1.45 mg/mL, respectively; p > 0.05). 5-Hydroxymethyl-furfural, a main compound in the extract of Zhi-heshouwu, showed IC50 values for scavenging DPPH radicals and hydroxyl radicals of 1.6 mg/mL and 0.24 mg/mL, respectively. The antioxidant activities of the extract from Zhi-heshouwu could partly explain the different therapeutic effects of Heshouwu and Zhi-heshouwu in TCM.

Possible involvement of advanced glycation end products in periodontal diseases

Periodontal diseases are considered as multifactorial conditions initiated by infection with pathogenic bacteria, promoted by inflammation and immune response against bacteria and modified by different environmental and genetic factors. Recently, interest in periodontal diseases has been increasing due to the awareness that the hyperinflammatory status associated with this disorder could impose a significant increase of reactive oxygen species (ROS) relevant to numerous systemic diseases driven by a pro-oxidant profile. A highly complex interplay occurs between oxidative stress and AGEs (Advanced Glycation End products), a group of heterogeneous compounds that form constantly under physiologic conditions, although their rate of formation is markedly increased in hyperglycemia and oxidizing conditions. Starting from the most relevant hypotheses on the pathogenesis of periodontal diseases, the present review outlines its relationship with oxidative stress and inflammation response in order to make a critical evaluation of the potential role of AGEs in periodontal deterioration. Although direct evidence for the presence of AGEs in the periodontal ligament is still lacking, valuable approaches based on the use of periodontal cells along with genetic and biochemical studies in animal models and chronic periodontal patients support a potential role for protein glycation in the aetiology and severity of this disease. Following a review of the current literature, the present study highlights the need for further investigation on the presence of AGEs in the periodontal ligament as a means for the comprehension of the pathogenic mechanisms underlying periodontal diseases in order to develop prevention and treatment modalities for this dysfunction.

Dietary advanced glycation end products and aging

Advanced glycation end products (AGEs) are a heterogeneous, complex group of compounds that are formed when reducing sugar reacts in a non-enzymatic way with amino acids in proteins and other macromolecules. This occurs both exogenously (in food) and endogenously (in humans) with greater concentrations found in older adults. While higher AGEs occur in both healthy older adults and those with chronic diseases, research is progressing to both quantify AGEs in food and in people, and to identify mechanisms that would explain why some human tissues are damaged, and others are not. In the last twenty years, there has been increased evidence that AGEs could be implicated in the development of chronic degenerative diseases of aging, such as cardiovascular disease, Alzheimer’s disease and with complications of diabetes mellitus. Results of several studies in animal models and humans show that the restriction of dietary AGEs has positive effects on wound healing, insulin resistance and cardiovascular diseases. Recently, the effect of restriction in AGEs intake has been reported to increase the lifespan in animal models. This paper will summarize the work that has been published for both food AGEs and in vivo AGEs and their relation with aging, as well as provide suggestions for future research.

Advanced glycation end-products and the kidney

BACKGROUND

Advanced glycation end-products (AGEs) are increased in situations with hyperglycemia and oxidative stress such as diabetes mellitus. They are products of nonenzymatic glycation and oxidation of proteins and lipids. The kidney plays an important role in clearance and metabolism of AGEs.

METHODS

Medline and other relevant databases were searched. In addition, key review articles were scanned for relevant original publication. Finally, original data from our research group were also included.

RESULTS

Kidney podocytes and endothelial cells express specific receptors for AGEs. Their activation leads to multiple pathophysiological effects including hypertrophy with cell cycle arrest and apoptosis, altered migration, and generation of proinflammatory cytokines. AGEs have been primarily implicated in the pathophysiology of diabetic nephropathy and diabetic microvascular complications. AGEs are also involved in other primary renal diseases as well as in the development and progression of atherosclerosis. However, serum or plasma concentrations of AGEs do not correlate well with cardiovascular events in patients with chronic kidney disease (CKD). This is likely due to the fact that serum concentrations failed to correlate with AGEs deposited in target tissues. Several inhibitors of the AGE-RAGE axis are currently tested for various indications.

CONCLUSION

AGEs and their receptors are involved in the pathogenesis of vascular and kidney disease. The role of circulating AGEs as biomarkers for cardiovascular risk estimation is questionable. Whether putative inhibitors of AGEs will get the maturity for its therapeutic use in the future remains open.

B-Type Natriuretic Peptide Signal Peptide Circulates in Human Blood

Background— The diagnosis of cardiac necrosis such as myocardial infarction can be difficult and relies on the use of circulating protein markers like troponin. However, there is a clear need to identify circulating, specific biomarkers that can detect cardiac ischemia without necrosis.

Methods and Results— Using specific immunoassay and tandem mass spectrometry, we show that a fragment derived from the signal peptide of B-type natriuretic peptide (BNPsp) not only is detectable in cytosolic extracts of explant human heart tissue but also is secreted from the heart into the circulation of healthy individuals. Furthermore, plasma levels of BNPsp in patients with documented acute ST-elevation myocardial infarction (n=25) rise to peak values (≈3 times higher than the 99th percentile of the normal range) significantly earlier than the currently used biomarkers myoglobin, creatine kinase-MB, and troponin. Preliminary receiver-operating characteristic curve analysis comparing BNPsp concentrations in ST-elevation myocardial infarction patients and other patient groups was positive (area under the curve=0.97; P <0.001), suggesting that further, more rigorous studies in heterogeneous chest pain patient cohorts are warranted.

Conclusion— Our results demonstrate for the first time that BNPsp exists as a distinct entity in the human circulation and could serve as a new class of circulating biomarker with the potential to accelerate the clinical diagnosis of cardiac ischemia and myocardial infarction.

Clinical Trial Registration— URL: http://www.anzctr.org.au. Unique identifier: ACTRN12609000040268.

Increased concentration of two different advanced glycation end-products detected by enzyme immunoassays with new monoclonal antibodies in sera of patients with rheumatoid arthritis

Background

Levels of pentosidine (representative of advanced glycation end-products) in sera of patients with rheumatoid arthritis are increased when compared with sera of other diagnoses or healthy controls. These levels have been reported to correlate with clinical indices of rheumatoid arthritis activity and with laboratory markers of inflammation. The purpose of this study was to find out if these findings pertain to other advanced glycation end-products.

Methods

We have developed two immunoassays based on new monoclonal antibodies to advanced glycation end-products. Antibody 103-E3 reacts with an unidentified antigen, formed in the reaction of proteins with ribose, while antibody 8-C1 responds to N^ε-(carboxyethyl)lysine. We have used these monoclonal antibodies to measure levels of advanced glycation end-products in sera of patients with rheumatoid arthritis, systemic lupus erythematosus, osteoarthritis, and healthy controls. We calculated the correlations between advanced glycation end-product levels in rheumatoid arthritis sera and the Disease Activity Score 28 (DAS28), age, disease duration, CRP, anti-CCP, rheumatoid factor and treatment with corticosteroids, respectively.

Results

Levels of both glycation products were significantly higher in sera of patients with rheumatoid arthritis when compared with sera of patients with systemic lupus erythematosus, osteoarthritis, or the healthy controls. Neither the level of N^ε-(carboxyethyl)lysine nor the level of the 103-E3 antigen in rheumatoid arthritis sera correlated with the DAS28-scored rheumatoid arthritis activity. The levels of both antigens in rheumatoid arthritis sera did not correlate with age, gender, corticosteroid treatment, or levels of CRP, anti-CCP antibodies, and rheumatoid factor in sera.

Conclusions

We report highly specific increases in the levels of two advanced glycation end-products in sera of patients with rheumatoid arthritis. This increase could be explained neither by rheumatoid arthritis activity nor by inflammation. We propose a working hypothesis that presumes the existence of a link between advanced glycation end-product formation and induction of autoimmunity.

Dihydrochalcones: Implication in resistance to oxidative stress and bioactivities against advanced glycation end-products and vasoconstriction

Flavonoids are a group of polyphenol compounds with known antioxidant activities. Among them, dihydrochalcones are mainly found in apple leaves (Malus domestica). Glycosylated dihydrochalcones were previously found in large amounts in leaves of two genotypes of Malus with contrasting resistance to fire blight, a bacterial disease caused by Erwinia amylovora. In the present study we demonstrate that soluble polyphenol patterns comprised phloridzin alone or in combination with two additional dihydrochalcones, identified as sieboldin and trilobatin. Presence of sieboldin in young leaves correlated well with a high 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. Moreover, these leaves displayed enhanced tolerance to paraquat, a photooxidative-stress generating herbicide. Interestingly, phloridzin had a high activity in the oxygen radical absorbance capacity (ORAC) assay, but its presence alone in leaves did not correlate with tolerance to paraquat. In order to further characterise the activity of these compounds, we tested their ability to prevent oxidative-dependent formation of advanced glycation end-products (AGEs) and phenylephrine-induced contraction of isolated rat mesenteric arteries. The antioxidant capacity of sieboldin was clearly demonstrated by showing that this compound (i) prevented vasoconstriction and (ii) inhibited AGEs formation. Both assays provided interesting information concerning a potential use of sieboldin as a therapeutic. Hence, our results strongly argue for a bioactivity of dihydrochalcones as functional antioxidants in the resistance of Malus leaves to oxidative stress. In addition, we demonstrate for the first time that sieboldin is a powerful multipotent antioxidant, effective in preventing physiopathological processes. Further work should aim at demonstrating the potential use of this compound as a therapeutic in treating free radical-involving diseases.

Carbohydrate biomarkers for future disease detection and treatment

Carbohydrates are considered as one of the most important classes of biomarkers for cell types, disease states, protein functions, and developmental states. Carbohydrate "binders" that can specifically recognize a carbohydrate biomarker can be used for developing novel types of site specific delivery methods and imaging agents. In this review, we present selected examples of important carbohydrate biomarkers and how they can be targeted for the development of therapeutic and diagnostic agents. Examples are arranged based on disease categories including (1) infectious diseases, (2) cancer, (3) inflammation and immune responses, (4) signal transduction, (5) stem cell transformation, (6) embryo development, and (7) cardiovascular diseases, though some issues cross therapeutic boundaries.

Role of pyridoxamine in the formation of the Amadori/Heyns compounds and aggregates during the glycation of beta-lactoglobulin with galactose and tagatose

The effect of pyridoxamine on the Maillard reaction during the formation of conjugates of beta-lactoglobulin with galactose and tagatose under controlled conditions (pH 7, 0.44 aw, 40 and 50 degrees C, for 6 days) has been studied, for the first time, by means of the changes in reducing carbohydrates, formation of Amadori or Heyns compounds, and aggregates and browning development. The results showed the formation of interaction products between pyridoxamine and galactose or tagatose either in the presence or in the absence of beta-lactoglobulin, indicating that pyridoxamine competes with the free amino groups of beta-lactoglobulin for the carbonyl group of both carbohydrates. Thus, a small inhibitory effect of pyridoxamine on the initial stages of the Maillard reaction was pointed out. Furthermore, much lower aggregation and color formation rates were observed in the conjugates of beta-lactoglobulin galactose/tagatose with pyridoxamine than without this compound, supporting its potent inhibitory effect on the advanced and final stages of the Maillard reaction. These findings reveal the usefulness of food-grade inhibitors of the advanced stages of the Maillard reaction, such as pyridoxamine, that, in combination with mild storage conditions, could lead to the formation of safer neoglycoconjugates without impairing their nutritional quality.

Maillard reaction, mitochondria and oxidative stress: potential role of antioxidants

Glycation and oxidative stress are two important processes known to play a key role in complications of many disease processes. Oxidative stress, either via increasing reactive oxygen species (ROS), or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo. Maillard Reactions, occur in vivo as well as in vitro and are associated with the chronic complications of diabetes, aging and age-related diseases. Hyperglycaemia causes the autoxidation of glucose, glycation of proteins, and the activation of polyol metabolism. These changes facilitate the generation of reactive oxygen species and decrease the activity of antioxidant enzymes such as Cu,Zn-superoxide dismutase, resulting in a remarkable increase of oxidative stress. A large body of evidence indicates that mitochondria alteration is involved and plays a central role in various oxidative stress-related diseases. The damaged mitochondria produce more ROS (increase oxidative stress) and less ATP (cellular energy) than normal mitochondria. As they are damaged, they cannot burn or use glucose or lipid and cannot provide cell with ATP. Further, glucose, amino acids and lipid will not be correctly used and will accumulate outside the mitochondria; they will undergo more glycation (as observed in diabetes, obesity, HIV infection and lipodystrophia). The objective of this paper is to discuss how to stop the vicious circle established between oxidative stress, Maillard Reaction and mitochondria. The potential application of some antioxidants to reduce glycation phenomenon and to increase the antioxidant defence system by targeting mitochondria will be discussed. Food and pharmaceutical companies share the same challenge, they must act now, urgently and energetically.

Glycation isotopic labeling with 13C-reducing sugars for quantitative analysis of glycated proteins in human plasma

Non-enzymatic glycation of proteins is a post-translational modification produced by a reaction between reducing sugars and amino groups located in lysine and arginine residues or in the N-terminal position. This modification plays a relevant role in medicine and food industry. In the clinical field, this undesired role is directly linked to blood glucose concentration and therefore to pathological conditions derived from hyperglycemia (>11 mm glucose) such as diabetes mellitus or renal failure. An approach for qualitative and quantitative analysis of glycated proteins is here proposed to achieve the three information levels for their complete characterization. These are: 1) identification of glycated proteins, 2) elucidation of sugar attachment sites, and 3) quantitative analysis to compare glycemic states. Qualitative analysis was carried out by tandem mass spectrometry after endoproteinase Glu-C digestion and boronate affinity chromatography for isolation of glycated peptides. For this purpose, two MS operational modes were used: higher energy collisional dissociation-MS2 and CID-MS3 by neutral loss scan monitoring of two selective neutral losses (162.05 and 84.04 Da for the glucose cleavage and an intermediate rearrangement of the glucose moiety). On the other hand, quantitative analysis was based on labeling of proteins with [(13)C(6)]glucose incubation to evaluate the native glycated proteins labeled with [(12)C(6)]glucose. As glycation is chemoselective, it is exclusively occurring in potential targets for in vivo modifications. This approach, named glycation isotopic labeling, enabled differentiation of glycated peptides labeled with both isotopic forms resulting from enzymatic digestion by mass spectrometry (6-Da mass shift/glycation site). The strategy was then applied to a reference plasma sample, revealing the detection of 50 glycated proteins and 161 sugar attachment positions with identification of preferential glycation sites for each protein. A predictive approach was also tested to detect potential glycation sites under high glucose concentration.

Mass spectrometric investigation of molecular variability of grass pollen group 1 allergens

Natural grass pollen allergens exhibit a wide variety of isoforms. Precise characterization of such microheterogeneity is essential to improve diagnosis and design appropriate immunotherapies. Moreover, standardization of allergen vaccine production is a prerequisite for product safety and efficiency. Both qualitative and quantitative analytical methods are thus required to monitor and control the huge natural variability of pollens, as well as final product quality. A proteomic approach has been set up to investigate in depth the structural variability of five group 1 allergens originating from distinct grass species (Ant o 1, Dac g 1, Lol p 1, Phl p 1, and Poa p 1). Whereas group 1 is the most conserved grass pollen allergen, great variations were shown between the various isoforms found in these five species using mass spectrometry, with many amino acid exchanges, as well as variations in proline hydroxylation level and in main N-glycan motifs. The presence of O-linked pentose residues was also demonstrated, with up to three consecutive units on the first hydroxyproline of Ant o 1. In addition, species-specific peptides were identified that might be used for product authentication or individual allergen quantification. Lastly, natural or process-induced modifications (deamidation, oxidation, glycation) were evidenced, which might constitute useful indicators of product degradation.

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.