Age- and stage-dependent accumulation of advanced glycation end products in intracellular deposits in normal and Alzheimer's disease brains

In this immunohistochemical study, the age- and stage-dependent accumulation of advanced glycation end-products (AGEs) in Alzheimer's disease (AD) and their relation to the formation of neurofibrillary tangles and neuronal cell death was investigated. For this purpose, the distribution of AGEs in neurons and glia was analyzed in the auditory association area of superior temporal gyrus (Brodmann area 22) of young and old non-demented controls and compared with early- and late-stage AD. A possible co-localization of AGEs with typical hallmarks of AD, such as hyperphosphorylated tau (as a marker for disturbed kinase/phosphatase activity), nNOS (as a marker for nitroxidative stress) and caspase-3 (as a marker of apoptotic cell death), was also investigated. Our results show that the percentage of AGE-positive neurons (and astroglia) increase both with age and, in AD patients, with the progression of the disease (Braak stages). Interestingly, nearly all if those neurons which show diffuse cytosolic AGE immunoreactivity also contain hyperphosphoryated tau, suggesting a link between AGE accumulation and the formation of early neurofibrillary tangles. Many, but not all, neurons show a co-localization of AGEs with other markers of neurodegeneration, such as nNOS and caspase-3

Immunochemical crossreactivity of antibodies specific for "advanced glycation endproducts" with "advanced lipoxidation endproducts"

Antibodies against advanced glycation endproducts (AGEs) are used for their immunohistological localization in tissues, for example in Alzheimer’s disease (AD) or diabetes. Many monoclonal and polyclonal antibodies have been used, and their specificity is unknown in most cases. Increased radical production, leading to the formation of lipid-derived reactive carbonyl species, such as malondialdehyde (MDA), acrolein, and glyoxal, is a characteristic aspect of age-related diseases like Alzheimer’s disease or diabetic polyneuropathy. These reactive carbonyl species are able to modify proteins, resulting in AGE related structures, termed “advanced lipoxidation products” (ALEs). In this study, the monoclonal carboxymethyllysine-specific antibody 4G9 and the polyclonal AGE-antibody K2189 were tested for their immunoreactivity towards these carbonyl-derived protein modifications. To investigate which carbonyl-modified amino acid side chains are specifically recognized by these antibodies, peptide membranes were incubated with glyoxal, MDA and acrolein. As model proteins, microtubuli associated protein tau (MAP-tau), β-amyloid, human serum albumin and chicken egg albumin were incubated likewise. It was found that both antibodies detected reaction products of these carbonyl compounds on lysine- and arginine residues and for the protein modification, it was found that some epitopes might not be detected. In conclusion, AGE-antibodies might not only detect sugar-derived AGEs but also structures derived from lipid peroxidation products (serving as markers of oxidative stress)

Comparison of Plasma and Urine Biomarker Performance in Acute Kidney Injury.

New renal biomarkers measured in urine promise to increase specificity for risk stratification and early diagnosis of acute kidney injury (AKI) but concomitantly may be altered by urine concentration effects and chronic renal insufficiency. This study therefore directly compared the performance of AKI biomarkers in urine and plasma.This single-center, prospective cohort study included 110 unselected adults undergoing cardiac surgery with cardiopulmonary bypass between 2009 and 2010. Plasma and/or urine concentrations of creatinine, cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), liver fatty acid-binding protein (L-FABP), kidney injury molecule 1 (KIM1), and albumin as well as 15 additional biomarkers in plasma and urine were measured during the perioperative period. The primary outcome was AKI defined by AKIN serum creatinine criteria within 72 hours after surgery.Biomarkers in plasma showed markedly better discriminative performance for preoperative risk stratification and early postoperative (within 24h after surgery) detection of AKI than urine biomarkers. Discriminative power of urine biomarkers improved when concentrations were normalized to urinary creatinine, but urine biomarkers had still lower AUC values than plasma biomarkers. Best diagnostic performance 4h after surgery had plasma NGAL (AUC 0.83), cystatin C (0.76), MIG (0.74), and L-FAPB (0.73). Combinations of multiple biomarkers did not improve their diagnostic power. Preoperative clinical scoring systems (EuroSCORE and Cleveland Clinic Foundation Score) predicted the risk for AKI (AUC 0.76 and 0.71) and were not inferior to biomarkers. Preexisting chronic kidney disease limited the diagnostic performance of both plasma and urine biomarkers.In our cohort plasma biomarkers had higher discriminative power for risk stratification and early diagnosis of AKI than urine biomarkers. For preoperative risk stratification of AKI clinical models showed similar discriminative performance to biomarkers. The discriminative performance of both plasma and urine biomarkers was reduced by preexisting chronic kidney disease

Ranking of candidate urine biomarkers.

<p>Ranking of biomarkers in urine according to their preoperative (pre-OP) and postoperative (4h and 24h after CPB) AUC-ROC performance for risk stratification and detection of AKI. AUC values <0.5 were expressed as 1-AUC indicated by AUC−. Parameters marked with * were not included in the Human KidneyMAP^® and were measured separately. The confidence intervals for AUCs were calculated with the DeLong method. Abbreviations: CTGF, connective tissue growth factor; CysC, Cystatin C; GSTα, glutathione S-transferase-α; IL18, interleukin 18; KIM1, kidney injury molecule 1; L-FABP, liver-type fatty acid-binding protein; NGAL neutrophil gelatinase-associated lipocalin; THP, Tamm-Horsfall protein; TIMP1, tissue inhibitor of metalloproteinases 1; TFF3, trefoil factor 3; VEGF, vascular endothelial growth factor.</p

Diagnostic performance of biomarkers in urine.

<p>Receiver operating characteristic curves (AUC-ROC) show discriminative abilities for preoperative risk stratification (pre-OP) and postoperative diagnosis of AKI (at 2h, 4h and 24h after CPB) for all patients (solid thick line) and separately for patients with (sold thin line) and without (dashed line) preexisting CKD. Indicated are AUC (p-value).</p

Ranking of candidate plasma biomarkers.

<p>Ranking of biomarkers in plasma according to their preoperative (pre-OP) and postoperative (4h and 24h after CPB) AUC-ROC performance for risk stratification and detection of AKI. AUC values <0.5 were expressed as 1-AUC indicated by AUC−. Parameters marked with * were measured with the assays indicated in the methods section, all others were measured using the Human CustomMAP. The confidence intervals for AUCs were calculated with the DeLong method. Abbreviations: BAFF, B-cell activating factor; BLC, B lymphocyte chemoattractant, chemokine C-X-C motif ligand (CXCL) 13; CKINE-6, chemokine with 6 cysteines, chemokine C-C motif ligand (CCL) 21; CysC, cystatin C; ICAM-1, intercellular adhesion molecule 1, cluster of differentiation (CD) 54; IP10, interferon-γ-induced protein 10, CXCL 10; ITAC, interferon-inducible T-cell alpha chemoattractant, CXCL11, IP9; L-FABP, liver-type fatty acid-binding protein; MCP-1, monocyte chemotactic protein-1, CCL2; MIG, monokine induced by interferon-γ, CXCL9; MIP3B, macrophage inflammatory protein-3ß, CCL19; NGAL, neutrophil gelatinase-associated lipocalin; SDF-1, stromal cell-derived factor-1, CXCL12; S-RAGE, soluble receptor for advanced glycosylation end products.</p