Advanced glycation end-products (AGEs) are lower in prostate tumor tissue and inversely related to proportion of West African ancestry.

BACKGROUND: The metabolism of normal prostate relies on glycolysis, with prostate cancer having reduced glycolysis and increased aerobic metabolism. Advanced glycation end products (AGEs) accumulate in tissues as a result of age and glycolytic rate. Differential AGE levels were recently observed in prostate cancer tissues. Herein we sought to quantify AGEs in benign and cancer prostate tissue in a diverse cohort of patients. METHODS: Levels of the AGE Nε-(carboxylethyl)lysine (CML) were quantified by immunohistochemistry (IHC) in a tissue microarray which consisted of 3 cores from tumor and 2 cores from benign areas from 118 patients (87 African American and 31 European American). Ancestry informative markers for African Ancestry were available for 79 patients. Epithelial and stromal areas were quantified separately using an E-cadherin mask. CML levels were compared with clinical grade group and ancestry by mixed linear effect models. Age, prostate-specific antigen (PSA) levels, body mass index (BMI), and hemoglobin A1C were included as covariates. RESULTS: CML levels were lower in areas of the tumor, for both epithelium and surrounding stroma, compared with benign, but did not significantly change with tumor grade group. Age, PSA levels, BMI, and hemoglobin A1C did not associate with CML levels. CML levels were inversely associated with the percentage of African Ancestry in all tissues. CONCLUSIONS: The low CML levels in cancer may reflect the reduced glycolytic state of the tissue. The inverse relationship between African Ancestry and CML levels in both benign and cancer areas suggests a state of reduced glycolysis. It is yet to be determined whether altered glycolysis and CML levels are bystanders or drivers of carcinogenesis.

Characterization of bromelain indicates a molar excess of inhibitor vs. enzyme molecules, a Jacalin-like lectin and Maillard reaction products.

The phytotherapeutic bromelain is a heterogeneous protein mixture, extracted from pineapple stem, with high proteolytic activity based on cysteine proteases. Its global protein chemical composition was analyzed qualitatively and quantitatively by SDS-PAGE and RP-HPLC. A SDS-PAGE method with elaborate sample pretreatment was developed, to cope with the bromelain's self-digestion properties and the hypothetical disulfide scrambling during electrophoresis. Both can produce misleading results, if not considered. RP-HPLC was applied for its high separation power for bromelain proteinaceous compounds. A peak identification and assignment to different protein classes in bromelain was done by enzyme kinetics and MS. The method was successfully applied for the quantitative determination of the molar ratio between inhibitor and enzyme and resulted to be approximately 3:2. Bromelain contains, from a molar point of view, inhibitor molecules as major component, which thus might be considered as a natural pharmaceutical excipient in Bromelain, because it protects the enzymes against autolysis. We described two methods to separate the inhibitor fraction from the enzyme fraction, RP-HPLC and size exclusion chromatography. A pineapple derived Jacalin-like-lectin, herein called 'Anlec', was identified and quantified by RP-HPLC-MS in bromelain and its content was determined to be 5%, related to all proteins in bromelain. Anlec binds specifically to mannose-containing glycans and is discussed in literature to possess anti-HIV medical potential. Bromelain could therefore be a possible and economic source for the production of Anlec. An isolation strategy of Anlec from bromelain, in high purity, is shown in this work. The presented RP-HPLC results are comprehensive in chemical information, and the method is expedient to provide appropriate bromelain protein isolations but also to accomplish quality control, covering all relevant protein components. It is furthermore shown, that proteins in bromelain may react with reducing sugars in a Maillard reaction to form glycated proteins. Maillard reaction products in bromelain are detected and characterized and could be responsible for the limited stability and storage times at room temperature of bromelain. Even the active center thiol group could be potentially glycated.

Determination of Free-Form and Peptide Bound Pyrraline in the Commercial Drinks Enriched with Different Protein Hydrolysates.

Pyrraline, a causative factor for the recent epidemics of diabetes and cardiovascular disease, is also employed as an indicator to evaluate heat damage and formation of advanced glycation end-products (AGEs) in foods. Peptide-enriched drinks (PEDs) are broadly consumed worldwide due to rapid rate of absorption and perceived health effects. It can be hypothesized that PED is an important source of pyrraline, especially peptide bound pyrraline (Pep-Pyr). In this study we determined free-form pyrraline (Free-Pyr) and Pep-Pyr in drinks enriched with whey protein hydrolysate (WPH), soy protein hydrolysate (SPH) and collagen protein hydrolysate (CPH). A detection method was developed using ultrahigh-performance liquid chromatography with UV-visible detector coupled with tandem mass spectrometry after solid-phase extraction (SPE). The SPE led to excellent recovery rates ranging between 93.2% and 98.5% and a high reproducibility with relative standard deviations (RSD) of <5%. The limits of detection and quantification obtained were 30.4 and 70.3 ng/mL, respectively. Pep-Pyr was identified as the most abundant form (above 96 percent) of total pyrraline, whereas Free-Pyr was present in a small proportion (less than four percent) of total pyrraline. The results indicate that PED is an important extrinsic source of pyrraline, especially Pep-Pyr. As compared with CPH- and SPH-enriched drinks, WPH-enriched drinks contained high content of Pep-Pyr. The Pep-Pyr content is associated with the distribution of peptide lengths and the amino acid compositions of protein in PEDs.

Redox proteomics: Methods for the identification and enrichment of redox-modified proteins and their applications.

PTMs are defined as covalent additions to functional groups of amino acid residues in proteins like phosphorylation, glycosylation, S-nitrosylation, acetylation, methylation, lipidation, SUMOylation as well as oxidation. Oxidation of proteins has been characterized as a double-edged sword. While oxidative modifications, in particular of cysteine residues, are widely involved in the regulation of cellular homeostasis, oxidative stress resulting in the oxidation of biomolecules along with the disruption of their biological functions can be associated with the development of diseases, such as cancer, diabetes, and neurodegenerative diseases, respectively. This is also the case for advanced glycation end products, which result from chemical reactions of keto compounds such as oxidized sugars with proteins. The role of oxidative modifications under physiological and pathophysiological conditions remains largely unknown. Recently, novel technologies have been established that allow the enrichment, identification, and characterization of specific oxidative PTMs (oxPTMs). This is essential to develop strategies to prevent and treat diseases that are associated with oxidative stress. Therefore this review will focus on (i) the methods and technologies, which are currently applied for the detection, identification, and quantification of oxPTMs including the design of high throughput approaches and (ii) the analyses of oxPTMs related to physiological and pathological conditions.

The effect of an AGE-rich dietary extract on the activation of NF-κB depends on the cell model used.

Advanced glycation end products (AGEs) are the results of a chemical reaction of reactive aldehydes, such as sugars, with amino acid side chains. AGEs can be formed by the heating process of the food and taken up with the diet. They are thought to be at least in part responsible for major complications in age-related diseases. The activation of the transcription factor NF-κB plays a prominent role in AGE-induced cell signaling. This study aimed to elucidate the effect of exogenous AGEs on NF-κB activation in different cell models. Therefore a bread crust extract commonly found in a Western diet was chosen as an AGE-rich sample. Using RP-HPLC, 23 fractions from the bread crust extract were obtained. The immunodetection with specific antibodies for N-carboxymethyllysine arg-pyrimidine, pentosidine and 3-deoxyglucosone-imidazolone showed that the majority of the AGEs were located in the late fractions. Three different NF-κB reporter cell lines including NF-κB/293/GFP-Luc™, NF-κB/Jurkat/GFP™ and RAW/NF-κB/SEAPorter™ were stimulated with the 23 fractions. There was no direct correlation between the AGE content in the fractions and the cell activation. Whereas in Jurkat-T-cells, the stimulation seems to correlate at least in part with the AGE content, in HEK-293 epithelial cell nearly all fractions can stimulate NF-κB. In macrophages few fractions stimulate NF-κB whereas some fractions even inhibit the p38 MAP kinase. The highest expression of the AGE receptors like RAGE, AGER-1, AGER-2 and AGER-3 was detected in the macrophage RAW cell line. In conclusion the present study showed a new approach to study bioactive compounds in bread crust extract. The identification of the bioactive compounds is still ongoing.

Analysis of protein glycation using phenylboronate acrylamide gel electrophoresis.

Carbohydrate modification of proteins adds complexity and diversity to the proteome. However, undesired carbohydrate modifications also occur in the form of glycation, resulting in diseases such as diabetes, Alzheimer's disease, autoimmune diseases, and cancer. The analysis of glycated proteins is challenging due to their complexity and variability. Numerous analytical techniques have been developed that require expensive specialised equipment and complex data analysis. In this chapter, we describe a simple electrophoresis-based method that enables users to detect, identify, and analyze these post-translational modifications. This new cost-effective methodology will aid the detection of unwanted glycation products in processed foods and may lead to new diagnostics and therapeutics for age-related chronic diseases and glycosylation disorders.

Bioguided fractionation and isolation of natural inhibitors of advanced glycation end-products (AGEs) from Calophyllum flavoramulum.

Advanced glycation end-products (AGEs) are associated with many pathogenic disorders such as Alzheimer's disease, pathogenesis of diabetes, atherosclerosis or endothelial dysfunction leading to cardiovascular events. Clusiaceae and Calophyllaceae families are rich in compounds like polyphenols which are able to inhibit their formation and are therefore of great interest. Calophyllum flavoramulum Hend. & Wyatt-Sm., a native Malaysian plant, was selected after an anti-AGEs screening conducted on DCM and MeOH extracts from plants belonging to these aforementioned families. In a first study, bioguided fractionation of the MeOH leaf extract of C. flavoramulum afforded amentoflavone, 3-methoxy-2-hydroxyxanthone, 3,4-dihydroxy-tetrahydrofuran-3-carboxylic acid, quercitrin, 3,4-dihydroxybenzoic acid, canophyllol and apetalactone. Amentoflavone and 3-methoxy-2-hydroxyxanthone were found to be very potent (IC(50)=0.05 and 0.06 mM respectively), while anti-AGEs activities of quercitrin and 3,4-dihydroxybenzoic acid appeared as moderately strong (IC(50)=0.5 mM). In a second study, a systematic phytochemical study of the cyclohexane, DCM and EtOAc extracts obtained from the same plant was conducted to isolate the following products: flavoramulone, 6-deoxyjacareubin, rheediachromenoxanthone, 2,3-dihydroamentoflavone and benzoic acid. 3,4-Dihydroxy-tetrahydrofuran-3-carboxylic acid and flavoramulone were isolated for the first time and their structures were identified by means of IR, MS and NMR spectrometries.

In vitro-prepared advanced glycation end-products and the modulating potential of their low-molecular weight degradation products in IRPTC-A rat proximal-tubular derived kidney epithelial cell line.

Low-molecular advanced glycation end-products (AGEs)-degradation products resulting from a proteolysis of tissue or circulating AGEs represent up to 80% of AGE plasma immunoreactivity. These AGE peptides contribute to the dramatic increase in AGE levels in end-stage renal disease even in the absence of diabetes. Because glomerular filtered AGE-degradation products may accumulate within intracellular compartments of proximal tubular epithelial cells, we investigated whether there is a pathway potentially mediating damaging effects of AGE-degradation products by perturbation of the function of the tubuloepithelium. Proximal tubular-derived rat kidney cells (IRPTC) were incubated with high-molecular AGEs highly modified by incubation of bovine serum albumin (BSA) with glucose for 50 days in vitro, and with low-molecular AGE-degradation products derived from proteolytic cleavage and isolated in the molecular range between 1 and 30 kDa. The proliferation of IRPTC (3H-thymidine incorporation) was reduced to 89+/-1% and 69+/-2% after 24 hr of incubation with BSA-AGE and BSA-AGE-degradation products, respectively. The cell viability of IRPTC was reduced significantly to 59+/-15% and 31+/-13% after 144 hr of incubation with BSA-AGE and BSA-AGE-degradation products, respectively. Conditioned media obtained from IRPTC incubated for 72 hr with BSA-AGE and its degradation products increased the proliferation rate of renal fibroblasts (RFb) to 222+/-24% and 449+/-40%, respectively. Incubation of IRPTC with BSA-AGE-degradation products increased the expression of endothelin-1 (ET-1) mRNA to 210% after 1 hr; the expression of platelet-derived growth factor-B (PDGF-B) mRNA reached 184% after 2 hr. Regarding the toxicity of AGEs to the kidney, low-molecular weight AGE-degradation products possibly form an individual fraction with a comparatively higher toxic potential.

Aislamiento de productos finales de la glucosilación avanzada por cromatografía de afinidad / Isolation of advanced glycosylation end products by affinity chromatography

Se describió un procedimiento para obtener productos finales de la glucosilación avanzada a partir de una mezcla de albúmina que había sido glucosilada e incubada a 37 ºC en condiciones de esterilidad, oscuridad y en presencia de glucosa por 6 sem. Se empleó la cromatografía de afinidad con matriz de lisozima para aislar los péptidos glucosilados que eluyeron con hidróxido de sodio 0,1 N. Se determinó la densidad óptica a 280 nm de cada fracción. Se observó que las fracciones eluidas de la mezcla de albúmina y glucosa, describieron una curva con un área mayor que la mezcla de albúmina sin glucosa, este hecho coincidió con lo planteado en otros trabajos. Se concluyó que la cromatografía de afinidad con matriz de lisozima es un método eficaz para aislar los productos finales de la glucosilación avanzada. Se planteó que estos productos podrían emplearse para elaborar métodos inmunoquímicos de detección en la sangre, tejidos u otros líquidos corporales. Las lecturas de las densidades ópticas fueron útiles para demostrar los péptidos glucosilados que eluyeron(AU)

Differential expression of receptors for advanced glycation end products on monocytes in patients with IDDM.

Accelerated modification of proteins by glucose terminating in the formation of advanced glycation endproducts (AGEs) is one of the main pathogenetic mechanisms of diabetes-associated complications. One pathway by which AGEs may exert their effects is by interaction with specific receptors initially identified on macrophages, monocytes and endothelial cells. As AGE-induced autocrine upregulation of AGE receptors has been observed in vitro, we hypothesized that AGE-binding might be enhanced in diabetic patients to compensate for the elevated levels of circulating AGEs. We therefore examined the expression of AGE-binding sites on peripheral monocytes, serum levels of AGEs and AGE-induced cytokine production in patients with insulin-dependent diabetes mellitus (IDDM) compared to age-matched, healthy control subjects. In patients, AGE-binding capacity was significantly increased and there was only one class of binding sites, as revealed by Scatchard analysis (1.8 x 10(5) vs 1.4 x 10(5) binding sites per cell). Affinity of binding was, however, similar (Ka 1.5 x 10(6) vs 1.4 x 10(6) mol(-1)). Saturation of binding was reached at 2.0-3.0 micromol/l with AGE-bovine serum albumin (BSA) as ligand. In contrast, cytometry using fluorescein isothiocyanate-labelled AGE-proteins showed no saturability and reversibility of AGE-binding up to 80 micromol/l, indicating non-specific binding in this concentration range. Again, this non-specific binding was significantly higher in IDDM patients. In addition, we found much higher levels of circulating AGEs in patients as compared to controls and studied possible functional consequences of increased AGE binding in vitro, monocyte stimulation by AGEs triggering cytokine release to a similar extent in patients and controls, i.e. independently of the AGE-binding capacity. Our finding of an enhanced overall AGE-binding capacity of peripheral monocytes in IDDM could be instrumental in limiting the plasma concentration of AGEs, the non-specific binding coming into play after saturation of specific binding sites by higher plasma AGE-levels. Both binding strategies may act in concert as "damage limitation mechanisms" in the development of AGE-dependent diabetic complications.

Tobacco smoke is a source of toxic reactive glycation products.

Smokers have a significantly higher risk for developing coronary and cerebrovascular disease than nonsmokers. Advanced glycation end products (AGEs) are reactive, cross-linking moieties that form from the reaction of reducing sugars and the amino groups of proteins, lipids, and nucleic acids. AGEs circulate in high concentrations in the plasma of patients with diabetes or renal insufficiency and have been linked to the accelerated vasculopathy seen in patients with these diseases. Because the curing of tobacco takes place under conditions that could lead to the formation of glycation products, we examined whether tobacco and tobacco smoke could generate these reactive species that would increase AGE formation in vivo. Our findings show that reactive glycation products are present in aqueous extracts of tobacco and in tobacco smoke in a form that can rapidly react with proteins to form AGEs. This reaction can be inhibited by aminoguanidine, a known inhibitor of AGE formation. We have named these glycation products "glycotoxins." Like other known reducing sugars and reactive glycation products, glycotoxins form smoke, react with protein, exhibit a specific fluorescence when cross-linked to proteins, and are mutagenic. Glycotoxins are transferred to the serum proteins of human smokers. AGE-apolipoprotein B and serum AGE levels in cigarette smokers were significantly higher than those in nonsmokers. These results suggest that increased glycotoxin exposure may contribute to the increased incidence of atherosclerosis and high prevalence of cancer in smokers.

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.

The endothelial cell binding site for advanced glycation end products consists of a complex: an integral membrane protein and a lactoferrin-like polypeptide.

Advanced glycation end products (AGEs), formed as the result of the extended interaction of proteins with ketoses, modulate central properties of endothelial cells and mononuclear phagocytes by interacting with a cell surface binding site comprised of a novel integral membrane protein (receptor for AGE = RAGE) and a lactoferrin-like polypeptide (LF-L), the latter having sequence identity to lactoferrin (LF). To further understand this cellular binding site, the interaction of RAGE with LF-L and LF was characterized. By ligand blotting and a solid state competitive binding assay, 125I-LF-L and 125I-LF bound to RAGE immobilized on nitrocellulose membranes or polypropylene tubes in a time-dependent and reversible manner, demonstrating a high affinity component with Kd approximately 100 pM. The interaction of 125I-LF-L and 125I-LF with RAGE was independent of iron in LF and was competed by addition of an excess of unlabeled carboxyl-terminal portion of LF. Cross-linking studies with purified 125I-LF-L and RAGE, in the presence of disuccinimidyl suberate, showed a new, slowly migrating band, corresponding to a complex of RAGE and LF-L, and cross-linking on mouse aortic endothelial cells showed two new slowly migrating bands on immunoblotting visualized with both anti-RAGE IgG and anti-LF-L IgG. These data lead us to propose that the endothelial cell surface binding site for AGEs consists of LF-L bound noncovalently to RAGE anchored in the cell membrane.

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.