Intraneuronal advanced glycation endproducts in presenilin-1 Alzheimer's disease

A detection model for cognitive dysfunction based on volatile organic compounds from a large Chinese community cohort

INTRODUCTION

We explored whether volatile organic compound (VOC) detection can serve as a screening tool to distinguish cognitive dysfunction (CD) from cognitively normal (CN) individuals.

METHODS

The cognitive function of 1467 participants was assessed and their VOCs were detected. Six machine learning algorithms were conducted and the performance was determined. The plasma neurofilament light chain (NfL) was measured.

RESULTS

Distinguished VOC patterns existed between CD and CN groups. The CD detection model showed good accuracy with an area under the receiver-operating characteristic curve (AUC) of 0.876. In addition, we found that 10 VOC ions showed significant differences between CD and CN individuals (p < 0.05); three VOCs were significantly related to plasma NfL (p < 0.005). Moreover, a combination of VOCs with NfL showed the best discriminating power (AUC = 0.877).

DISCUSSION

Detection of VOCs from exhaled breath samples has the potential to provide a novel solution for the dilemma of CD screening.

Is carbonyl/AGE/RAGE stress a hallmark of the brain aging?

Recent studies have linked carbonyl stress to many physiological processes. Increase in the levels of carbonyl compounds, derived from both endogenous and exogenous sources, is believed to accompany normal age-related decline as well as different pathologies. Reactive carbonyl species (RCS) are capable of damaging biomolecules via their involvement in a net of nonspecific reactions. In the advanced stages of RCS metabolism, variety of poorly degraded adducts and crosslinks, collectively named advanced glycoxidation end products (AGEs), arises. They are accumulated in an age-dependent manner in different tissues and organs and can contribute to inflammatory processes. In particular, detrimental effects of the end products are realized via activation of the specific receptor for AGEs (RAGE) and RAGE-dependent inflammatory signaling cascade. Although it is unclear, whether carbonyl stress is causal for age-associated impairments or it results from age- and disease-related cell damages, increased levels of RCS and AGEs are tightly related to inflammaging, and therefore, attenuation of the RAGE signaling is suggested as an effective approach for the treatment of inflammation and age-related disorders. The question raised in this review is whether specific metabolism in the aging brain related to carbonyl/RCS/AGE/RAGE stress.

Black Tea Theaflavin Detoxifies Metabolic Toxins in the Intestinal Tract of Mice

SCOPE

This study is to determine the in vivo efficacy of black tea theaflavin (TF) to detoxify two metabolic toxins, ammonia and methylglyoxal (MGO), in mice METHODS AND RESULTS: Under in vitro conditions, TF is able to react with ammonia, MGO, and hydrogen peroxide to produce its aminated, MGO conjugated, and oxidized products, respectively. In TF-treated mice, the aminated TF, the MGO conjugates of TF and aminated TF, and the oxidized TF are searched using LC-MS/MS. The results provide the first in vivo evidence that the unabsorbed TF is able to trap ammonia to form the aminated TF; furthermore, both TF and the aminated TF have the capacity to trap MGO to generate the corresponding mono-MGO conjugates. Moreover, TF is oxidized to dehydrotheaflavin, which underwent further amination in the gut. By exposing TF to germ-free (GF) mice and conventionalized mice (GF mice colonized with specific-pathogen-free microbiota), the gut microbiota is demonstrated to facilitate the amination and MGO conjugation of TF.

CONCLUSION

TF has the capacity to remove the endogenous metabolic toxins through oxidation, amination, and MGO conjugation in the intestinal tract, which can potentially explain why TF still generates in vivo efficacy while showing a poor systematic bioavailability.

Potentially Harmful Maillard Reaction Products in Food and Herb Medicines

The Maillard reaction is of great significance in food, herb medicines, and life processes. It is usually occurring during the process of food and herb medicines processing and storage. The formed Maillard reaction productions (MRPs) in food and herb medicines not only generate a large number of efficacy components but also generate a small amount of harmful substance that cannot be ignored. Some of the MRPs, especially the advanced glycation end products (AGEs) are concerning humans, based on the possibility to induce cancer and mutations in laboratory animals. Numerous studies have been reported on the formation, analysis, and control of the potentially harmful MRPs (PHMRPs). Therefore, the investigation into the formation, analysis, and control of PHMRPs in food and herb medicines is very important for improving the quality and safety of food and herb medicines. This article provides a brief review of the formation, analysis (major content), and control of PHMRPs in food and herb medicines, which will provide a base and reference for safe processing and storage of food and herb medicines. Practical Applications. The formed Maillard reaction productions in food and herb medicines not only generate a large number of functional components but also generate a small amount of harmful substance that cannot be ignored. This contribution provides a brief review on the formation (including the correlative studies between MRs and the PHMRPs, mechanisms, and the main pathways); analysis (major content, pretreatment for analysis, qualitative and quantitative analysis, and structural identification analysis); and control (strategies and mechanisms) of PHMRPs in food and herb medicines, which will provide a solid theoretical foundation and a valuable reference for safe processing and storage for food and herb medicines.

Acetoacetate enhancement of glucose mediated DNA glycation

Acetoacetate (AA) is a ketone body, which generates reactive oxygen species (ROS). ROS production is impacted by the formation of covalent bonds between amino groups of biomacromolecules and reducing sugars (glycation). Glycation can damage DNA by causing strand breaks, mutations, and changes in gene expression. DNA damage could contribute to the pathogenesis of various diseases, including neurological disorders, complications of diabetes, and aging. Here we studied the enhancement of glucose-mediated DNA glycation by AA for the first time. The effect of AA on the structural changes, Amadori and advanced glycation end products (AGEs) formation of DNA incubated with glucose for 4 weeks were investigated using various techniques. These included UV-Vis, circular dichroism (CD) and fluorescence spectroscopy, and agarose gel electrophoresis. The results of UV-Vis and fluorescence spectroscopy confirmed that AA increased the DNA-AGE formation. The NBT test showed that AA also increased Amadori product formation of glycated DNA. Based on the CD and agarose gel electrophoresis results, the structural changes of glycated DNA was increased in the presence of AA. The chemiluminescence results indicated that AA increased ROS formation. Thus AA has an activator role in DNA glycation, which could enhance the adverse effects of glycation under high glucose conditions.

Trapping Methylglyoxal by Myricetin and Its Metabolites in Mice

Trapping of methylglyoxal (MGO) has been determined to be one of the potential mechanisms for dietary polyphenols to prevent chronic diseases. In this study, myricetin was demonstrated to efficiently trap MGO to generate mono- and di-MGO adducts under in vitro conditions. Furthermore, the mono- and di-MGO adducts of myricetin were detected in urine and fecal samples collected from myricetin-treated mice based on LC-MS analysis. More importantly, the mono-MGO adducts of the mono- and di-methylated myricetin were also found in these mouse samples. Further dose-dependent studies demonstrated that myricetin and its methylated metabolites significantly trapped MGO in a dose-dependent manner with the 400 mg/kg dose having the highest trapping efficacy (mono-MGO-myricetin: 272.0 ± 90.9 nM in urine and 1.05 ± 0.67 μg/g in feces; mono-MGO-mono-Me-myricetin: 135.2 ± 77.6 nM in urine and 1.16 ± 0.65 μg/g in feces; and mono-MGO-di-Me-myricetin: 17.0 ± 5.9 nM in urine and 0.19 ± 0.04 μg/g in feces) compared to the 100 and 200 mg/kg doses. In conclusion, this study demonstrates for the first time the in vivo trapping efficacy of myricetin, suggesting that intake of myricetin-containing foods has the potential to scavenge MGO in vivo and to prevent MGO-induced harmful effects to human health.

Study of glycation process of human carbonic anhydrase II as well as investigation concerning inhibitory influence of 3-beta-hydroxybutyrate on it

Glycation is a non-enzymatic reaction between carbonyl groups in sugar and free amino groups in proteins. This reaction leads to changes in structure and functions of proteins in which the advanced glycation end products (AGEs) are the final outcome and cause many complications in diabetic patients. We herein examined the effect of fasting on the glycation process of human Carbonic anhydrase II under physiological conditions (37 °C and pH 7.4) employing various techniques, including Ultraviolet-visible spectroscopy, fluorescence spectroscopy and CD Spectroscopy. We found an increased 3-beta-hydroxybutyrate upon fasting. We studied various samples of control carbonic anhydrase (without glucose and 3-beta-hydroxybutyrate), carbonic anhydrase with glucose, carbonic anhydrase treated with 3-beta-hydroxybutyrate (BHB) and carbonic anhydrase along with glucose and 3-beta-hydroxybutyrate. The samples were incubated for 35 days under physiological conditions. Our results indicated that 3-beta-hydroxybutyrate inhibited the glycation process, decreased glucose binding to the protein, prevented the formation of AGEs, and modified the enzyme activity. Our findings would open new windows toward the enzymatic procedure which would have profound implication in understanding the diabetes mechanisms.

Benfotiamine treatment activates the Nrf2/ARE pathway and is neuroprotective in a transgenic mouse model of tauopathy

Impaired glucose metabolism, decreased levels of thiamine and its phosphate esters, and reduced activity of thiamine-dependent enzymes, such as pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase occur in Alzheimer's disease (AD). Thiamine deficiency exacerbates amyloid beta (Aβ) deposition, tau hyperphosphorylation and oxidative stress. Benfotiamine (BFT) rescued cognitive deficits and reduced Aβ burden in amyloid precursor protein (APP)/PS1 mice. In this study, we examined whether BFT confers neuroprotection against tau phosphorylation and the generation of neurofibrillary tangles (NFTs) in the P301S mouse model of tauopathy. Chronic dietary treatment with BFT increased lifespan, improved behavior, reduced glycated tau, decreased NFTs and prevented death of motor neurons. BFT administration significantly ameliorated mitochondrial dysfunction and attenuated oxidative damage and inflammation. We found that BFT and its metabolites (but not thiamine) trigger the expression of Nrf2/antioxidant response element (ARE)-dependent genes in mouse brain as well as in wild-type but not Nrf2-deficient fibroblasts. Active metabolites were more potent in activating the Nrf2 target genes than the parent molecule BFT. Docking studies showed that BFT and its metabolites (but not thiamine) bind to Keap1 with high affinity. These findings demonstrate that BFT activates the Nrf2/ARE pathway and is a promising therapeutic agent for the treatment of diseases with tau pathology, such as AD, frontotemporal dementia and progressive supranuclear palsy.

Effect of glycation inhibitors on aging and age-related diseases

Vast evidence supports the view that glycation of proteins is one of the main factors contributing to aging and is an important element of etiopathology of age-related diseases, especially type 2 diabetes mellitus, cataract and neurodegenerative diseases. Counteracting glycation can therefore be a means of increasing both the lifespan and healthspan. In this review, accumulation of glycation products during aging is presented, pathophysiological effects of glycation are discussed and ways of attenuation of the effects of glycation are described, concentrating on prevention of glycation. The effects of glycation and glycation inhibitors on the course of selected age-related diseases, such as Alzheimer's disease, Parkinson's disease and cataract are also reviewed.

Acetoacetate promotes the formation of fluorescent advanced glycation end products (AGEs)

Acetoacetate (AA) is an important ketone body, which produces reactive oxygen species (ROS). Advanced glycation end products (AGEs) are defined as final products of glycation process whose production is influenced by the levels of ROS. The accumulation of AGEs in the body contributes to pathogenesis of many diseases including complications of diabetes, and Alzheimer's and Parkinson's disease. Here, we evaluated the impact of AA on production of AGEs upon incubation of human serum albumin (HSA) with glucose. The effect of AA on the AGEs formation of HSA was studied under physiological conditions after incubation with glucose for 35 days. The physical techniques including circular dichroism (CD) and fluorescence spectroscopy were used to assess the impact of AA on formation and structural changes of glycated HSA (GHSA). Our results indicated that the secondary and tertiary structural changes of GHSA were increased in the presence of AA. The fluorescence intensity measurements of AGEs also showed an increase in AGEs formation. Acetoacetate has an activator effect in formation of AGEs through ROS production. The presence of AA may result in enhanced glycation in the presence of glucose and severity of complications associated with accumulation of AGEs.

Bioactive ginger constituents alleviate protein glycation by trapping methylglyoxal

Considerable evidence suggests that long-term pathological diabetes is a result of the accumulation of tissue macromolecules that have been progressively modified by nonenzymatic glycation of protein. Methylglyoxal (MGO) is a highly reactive endogenous dicarbonyl metabolite derived from multiple sources such as glucose and lipids and is thought to contribute greatly to protein glycation and the formation of advanced glycation end products (AGEs). In this study, we demonstrated for the first time that both [6]-shogaol (6S) and [6]-gingerol (6G), the major active components in ginger, markedly trapped MGO in vitro and consequently formed mono-MGO adducts, 6S-MGO and 6G-MGO, which were purified from the respective chemical reaction and characterized as novel compounds by NMR experiments and LC-MS/MS approaches. We revealed that the α-carbon of the carbonyl group in the side chain of 6S or 6G is the major active site for trapping MGO. We also demonstrated that 6S and 6G could effectively inhibit the formation of MGO-induced AGEs via trapping MGO in a time-dependent manner in the human serum albumin (HSA)-MGO system. Mono-MGO adducts, 6S-MGO and 6G-MGO, were determined to be the major conjugates in 6S- and 6G-treated HSA-MGO assays, respectively, using LC-ESI-MS techniques. These findings showed the potential effects of 6S and 6G on the prevention of protein glycation, suggesting regular consumption of ginger root extract may attenuate the progression of MGO-associated diabetic complications in patients.

Glycation of the high affinity NGF-receptor and RAGE leads to reduced ligand affinity

AGEs are posttranslational modifications generated by irreversible non-enzymatic crosslinking reactions between sugars and proteins - a reaction referred to as glycation. Glycation, a feature of ageing, can lead to non-degradable and less functional proteins and enzymes and can additionally induce inflammation and further pathophysiological processes such as neurodegeneration. In this study we investigated the influence of glycation on the high affinity NGF-receptor TrkA and the AGE-receptor RAGE. We quantified the binding affinity of the TrkA-receptor and RAGE to their ligands by surface plasmon resonance (SPR) and compared these to the binding affinity after glycation. At the same time, we established a glycation procedure using SPR. We found that glycation of TrkA reduced the affinity to NGF by a factor of three, which could be shown to lead to a reduction of NGF-dependent neurite outgrowth in PC12 cells. Glycation of RAGE reduced binding affinity of AGEs by 10-fold.

Decoding Alzheimer's disease from perturbed cerebral glucose metabolism: implications for diagnostic and therapeutic strategies

Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder, which severely impacts on the global economic development and healthcare system. Though AD has been studied for more than 100 years since 1906, the exact cause(s) and pathogenic mechanism(s) remain to be clarified. Also, the efficient disease-modifying treatment and ideal diagnostic method for AD are unavailable. Perturbed cerebral glucose metabolism, an invariant pathophysiological feature of AD, may be a critical contributor to the pathogenesis of this disease. In this review, we firstly discussed the features of cerebral glucose metabolism in physiological and pathological conditions. Then, we further reviewed the contribution of glucose transportation abnormality and intracellular glucose catabolism dysfunction in AD pathophysiology, and proposed a hypothesis that multiple pathogenic cascades induced by impaired cerebral glucose metabolism could result in neuronal degeneration and consequently cognitive deficits in AD patients. Among these pathogenic processes, altered functional status of thiamine metabolism and brain insulin resistance are highly emphasized and characterized as major pathogenic mechanisms. Finally, considering the fact that AD patients exhibit cerebral glucose hypometabolism possibly due to impairments of insulin signaling and altered thiamine metabolism, we also discuss some potential possibilities to uncover diagnostic biomarkers for AD from abnormal glucose metabolism and to develop drugs targeting at repairing insulin signaling impairment and correcting thiamine metabolism abnormality. We conclude that glucose metabolism abnormality plays a critical role in AD pathophysiological alterations through the induction of multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, and so forth. To clarify the causes, pathogeneses and consequences of cerebral hypometabolism in AD will help break the bottleneck of current AD study in finding ideal diagnostic biomarker and disease-modifying therapy.

Abnormal thiamine-dependent processes in Alzheimer's Disease. Lessons from diabetes

Reduced glucose metabolism is an invariant feature of Alzheimer's Disease (AD) and an outstanding biomarker of disease progression. Glucose metabolism may be an attractive therapeutic target, whether the decline initiates AD pathophysiology or is a critical component of a cascade. The cause of cerebral regional glucose hypometabolism remains unclear. Thiamine-dependent processes are critical in glucose metabolism and are diminished in brains of AD patients at autopsy. Further, the reductions in thiamine-dependent processes are highly correlated to the decline in clinical dementia rating scales. In animal models, thiamine deficiency exacerbates plaque formation, promotes phosphorylation of tau and impairs memory. In contrast, treatment of mouse models of AD with the thiamine derivative benfotiamine diminishes plaques, decreases phosphorylation of tau and reverses memory deficits. Diabetes predisposes to AD, which suggests they may share some common mechanisms. Benfotiamine diminishes peripheral neuropathy in diabetic humans and animals. In diabetes, benfotiamine induces key thiamine-dependent enzymes of the pentose shunt to reduce accumulation of toxic metabolites including advanced glycation end products (AGE). Related mechanisms may lead to reversal of plaque formation by benfotiamine in animals. If so, the use of benfotiamine could provide a safe intervention to reverse biological and clinical processes of AD progression. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Glyoxalase I retards renal senescence

Although kidney functions deteriorate with age, little is known about the general morphological alterations and mechanisms of renal senescence. We hypothesized that carbonyl stress causes senescence and investigated the possible role of glyoxalase I (GLO1), which detoxifies precursors of advanced glycation end products in the aging process of the kidney. We observed amelioration of senescence in GLO1-transgenic aged rats (assessed by expression levels of senescence markers such as p53, p21(WAF1/CIP1), and p16(INK4A)) and a positive rate of senescence-associated β-galactosidase (SABG) staining, associated with reduction of renal advanced glycation end product accumulation (estimated by the amount of carboxyethyl lysine). GLO1-transgenic rats showed amelioration of interstitial thickening (observed as an age-related presentation in human renal biopsy specimens) and were protected against age-dependent decline of renal functions. We used GLO1 overexpression or knockdown in primary renal proximal tubular epithelial cells to investigate the effect of GLO1 on cellular senescence. Senescence markers were significantly up-regulated in renal proximal tubular epithelial cells at late passage and in those treated with etoposide, a chemical inducer of senescence. GLO1 cellular overexpression ameliorated and knockdown enhanced the cellular senescence phenotypes. Furthermore, we confirmed the association of decreased GLO1 enzymatic activity and age-dependent deterioration of renal function in aged humans with GLO1 mutation. These findings indicate that GLO1 ameliorates carbonyl stress to retard renal senescence.

Variations in the neuropathology of familial Alzheimer's disease

Mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes cause autosomal dominant familial Alzheimer's disease (AD). PSEN1 and PSEN2 are essential components of the gamma-secretase complex, which cleaves APP to affect Abeta processing. Disruptions in Abeta processing have been hypothesised to be the major cause of AD (the amyloid cascade hypothesis). These genetic cases exhibit all the classic hallmark pathologies of AD including neuritic plaques, neurofibrillary tangles (NFT), tissue atrophy, neuronal loss and inflammation, often in significantly enhanced quantities. In particular, these cases have average greater hippocampal atrophy and NFT, more significant cortical Abeta42 plaque deposition and more substantial inflammation. Enhanced cerebral Abeta40 angiopathy is a feature of many cases, but particularly those with APP mutations where it can be the dominant pathology. Additional frontotemporal neuronal loss in association with increased tau pathology appears unique to PSEN mutations, with mutations in exons 8 and 9 having enlarged cotton wool plaques throughout their cortex. The mechanisms driving these pathological differences in AD are discussed.

Pentosidine accumulation in human oocytes and their correlation to age-related apoptosis

Age-related atresia of ovarian follicles is characterized by apoptosis of the constituent cells. Recent studies have indicated that dysfunction of the proteasome and endoplasmic reticulum and subsequent apoptosis in the presence of oxidative stress have relevance to aging. The aim of this study was to assess the involvement of these processes in age-related follicular atresia. Formalin-fixed, paraffin-embedded sections of ovaries obtained at surgery from 74 women (age: 21-54 y) were examined with the terminal deoxynucleotidyl transferase-mediated, dUTP-biotin nick-end labeling (TUNEL) method and an immunohistochemical technique. Primary antibodies used in immunohistochemistry were against pentosidine, ubiquitin and caspase 12. Histological localization of these substances in oocytes was observed by light microscopy, and labeling indices of these cells were evaluated by regression analysis. Positive signals for pentosidine, ubiquitin, caspase 12, and TUNEL were detectable in oocytes of the primordial, primary and their atretic follicles. Regression analysis revealed an age-related increase in the labeling indices for pentosidine, ubiquitin, caspase 12, and TUNEL. These results suggest that pentosidine accumulation in human oocytes is related to apoptosis and increases with age. Further studies will be necessary to clarify the involvement of pentosidine accumulation, proteasome inhibition, and endoplasmic reticulum stress in age-related apoptosis of oocytes in human ovaries.

Novel inhibitors of glycation and AGE formation

Accelerated formation of advanced glycation/lipoxidation and endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several natural and synthetic compounds have been proposed and tested as inhibitors of AGE/ALE formation. We have previously reported the therapeutic effects of several new AGE/ALE inhibitors on the prevention of nephropathy and dyslipidemia in streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the effects of various concentrations of a compound, LR-90, on the progression of renal disease and its effects on AGE and receptor for AGE (RAGE) protein expression on the kidneys of diabetic STZ-rats. Diabetic male Sprague-Dawley rats were treated with or without LR-90 (0, 5, 20, 25, and 50 mg/l of drinking water). After 32 weeks, body weight, glycemic status, renal function, and plasma lipids were measured. Kidney histopathology and AGE/ALE accumulation and RAGE protein expression in tissues were also determined. In vitro studies were also performed to determine the possible mechanism of action of LR-90 in inhibiting AGE formation and AGE-protein cross-linking. LR-90 protected the diabetic kidneys by inhibiting the increase in urinary albumin-to-creatinine ratio and ameliorated hyperlipidemia in diabetic rats in a concentration-dependent fashion without any effects on hyperglycemia. LR-90 treatment also reduced kidney AGE/ALE accumulation and RAGE protein expression in a concentration-dependent manner. In vitro, LR-90 exhibited general antioxidant properties by inhibiting metal-catalyzed reactions and reactive oxygen species (OH radical) and reactive carbonyl species (methlyglyoxal, glyoxal) generations without any effect on pyridoxal 5' phosphate. The compound also prevents AGE-protein cross-linking reactions. These findings demonstrate the bioefficacy of LR-90 in treating nephropathy and hyperlipidemia in diabetic animals by inhibiting AGE accumulation, RAGE protein expression, and protein oxidation in the diabetic kidney. Additionally, our study suggests that LR-90 may be useful also to delay the onset and progression of diabetic atherosclerosis as the compound can inhibit the expression of RAGE and inflammation-related pathology, as well as prevent lipid peroxidation reactions.

[Maillard reaction products in food as pro-inflammatory and pro-arteriosclerotic factors of degenerative diseases]

Heating of food induces the formation of Maillard reaction products (MRPs) caused by the reaction of reducing sugars with proteins or amino acids. Analogous reactions occur in the human body, eventually forming "Advanced Glycation Endproducts" (AGEs). AGEs accumulate in aging tissues accelerating degenerative-inflammatory and proliferative processes. MRPs present in food can also directly cause inflammatory processes in the intestines and, once absorbed, would support and reinforce any inflammatory and degenerative process occurring in the body. The contribution of AGEs (and additional MRPs) in the development of diabetic complications as well as nephropathy, neuropathy, micro- and macroangiopathies is now well established. Which of the MRPs or AGEs in particular induce these cellular processes is currently unknown. Thus the exact knowledge of the chemical structures of the MRPs could help to minimize the formation of "harmful MRPs" that occur due to heating in food processing. Because MRPs play a decisive role in the successful marketing of edibles due to their characteristics as flavor components, it is important to increase the amount of innocuous and palatable MRPs, and minimize signal active pro-inflammatory MRPs by the use of defined preparation methods. It is practicable to use low-priced immunological methods for the quantitative determination of specific MRPs or AGEs. In the medical area, the knowledge of the signal active MRP/AGE structures provides the opportunity to measure their concentrations in body fluids and tissues and thus determine their influence on inflammatory and age-related degenerative processes (e. g., late diabetic complications, arteriosclerosis, degeneration of neurons). From a clinical perspective, the application of RAGE antagonists after an appropriate chemical diagnosis could be effective in supporting the treatment of affected patient groups, especially older diabetic and dialysis patients.

Differences in regional brain atrophy in genetic forms of Alzheimer's disease

Multiple degenerative hallmarks characterize Alzheimer's disease: insoluble protein deposition, neuronal loss and cortical atrophy. Atrophy begins in the medial temporal lobe and becomes global by end stage. In a small proportion of cases, these tissue changes are caused by mutations in three known genes. These cases are affected earlier in life and have more abundant protein deposition, which may indicate greater tissue atrophy and degeneration. This issue remains unresolved. Grey matter atrophy in different cortical regions was determined in genetic cases of Alzheimer's disease (N = 13) and compared to sporadic cases (N = 13) and non-diseased controls (N = 23). Genetic mutations were found to influence the degree and regional pattern of atrophy. The majority of cases had greater medial temporal atrophy than sporadic disease, suggesting that abnormalities affecting Abeta metabolism selectively increase hippocampal degeneration. Cases with mutations in presenilin-1 demonstrated additional increased frontotemporal atrophy. This effect may be due to the influence of presenilin-1 on tau phosphorylation and metabolism. These differences may explain the earlier onset ages in these different forms of Alzheimer's disease.

Methylglyoxal downregulates Raf-1 protein through a ubiquitination-mediated mechanism

Abnormal accumulation of methylglyoxal, a physiological glucose metabolite, is considered a potential link between hyperglycemia and diabetes complications. Evidence has shown that methylglyoxal modifies cellular proteins by glycation and oxidation, resulting in dysfunction or loss of cellular proteins. Raf-1 protein-serine/threonine kinase serves as a central switch board in the transmission of many growth and developmental signals. It was reported that Raf-1 levels appear to decrease in some diabetic subjects. But the potential mechanisms have not yet been clarified. Here, we tested the hypothesis that methylglyoxal-mediated proteolysis might contribute to the downregulation of Raf-1 levels. We observed that a rapid and detectable decrease in Raf-1 protein levels was induced by methylglyoxal, which was accelerated by treating with a Raf-1 activator, phorbol-12-myristate-13-acetate, and by expressing active forms of Raf-1 and Ras. Moreover, immunoprecipitation and immunoblotting assays showed that co-treatment of cells with methylglyoxal and phorbol-12-myristate-13-acetate caused dramatic ubiquitination in both total intracellular proteins and Raf-1. Blocking phosphorylation with the protein kinase C inhibitor bisindolylmaleimide, or inhibiting intracellular oxidation by addition of the antioxidant N-acetyl-l-cysteine could reverse the ubiquitination and downregulation of Raf-1 induced by methylglyoxal and phorbol-12-myristate-13-acetate. These results suggest that methylglyoxal-mediated intracellular oxidation and ubiquitin/proteasome-dependent proteolysis are involved in the downregulation of Raf-1, which may be closely related to the development complications in diabetes.

Proteins in human brain cortex are modified by oxidation, glycoxidation, and lipoxidation. Effects of Alzheimer disease and identification of lipoxidation targets

Diverse oxidative pathways, such as direct oxidation of amino acids, glycoxidation, and lipoxidation could contribute to Alzheimer disease pathogenesis. A global survey for the amount of structurally characterized probes for these reactions is lacking and could overcome the lack of specificity derived from measurement of 2,4-dinitrophenylhydrazine reactive carbonyls. Consequently we analyzed (i) the presence and concentrations of glutamic and aminoadipic semialdehydes, N(epsilon)-(carboxymethyl)-lysine, N(epsilon)-(carboxyethyl)-lysine, and N(epsilon)-(malondialdehyde)-lysine by means of gas chromatography/mass spectrometry, (ii) the biological response through expression of the receptor for advanced glycation end products, (iii) the fatty acid composition in brain samples from Alzheimer disease patients and age-matched controls, and (iv) the targets of N(epsilon)-(malondialdehyde)-lysine formation in brain cortex by proteomic techniques. Alzheimer disease was associated with significant, although heterogeneous, increases in the concentrations of all evaluated markers. Alzheimer disease samples presented increases in expression of the receptor for advanced glycation end products with high molecular heterogeneity. Samples from Alzheimer disease patients also showed content of docosahexaenoic acid, which increased lipid peroxidizability. In accordance, N(epsilon)-(malondialdehyde)-lysine formation targeted important proteins for both glial and neuronal homeostasis such as neurofilament L, alpha-tubulin, glial fibrillary acidic protein, ubiquinol-cytochrome c reductase complex protein I, and the beta chain of ATP synthase. These data support an important role for lipid peroxidation-derived protein modifications in Alzheimer disease pathogenesis.

Novel inhibitors of advanced glycation endproducts

A number of natural or synthetic compounds as AGE inhibitors have been proposed, discovered or currently being advanced by others and us. We have identified two new classes of aromatic compounds; aryl- (and heterocyclic) ureido and aryl (and heterocyclic) carboxamido phenoxyisobutyric acids, and benzoic acid derivatives and related compounds, as potential inhibitors of glycation and AGE formation. Some of these novel compounds also showed "AGE-breaking" activities in vitro. Current evidence is that chelation of transition metals and/or trapping or indirect inhibition of formation of reactive carbonyl compounds are involved in the mechanisms of action of these novel AGE inhibitors and breakers. Here, we review the inhibitors of glycation and AGE-breakers published to date and present the results of our in vitro and in vivo investigations on a number of these novel AGE inhibitors. These AGE-inhibitors and AGE-breakers may find therapeutic use in the treatment of diseases that AGE formation and accumulation may be responsible for their pathogenesis such as diabetes, Alzheimer's, rheumatoid arthritis, and atherosclerosis.

Spatial patterns of mammalian brain aging: distribution of cathepsin D-immunoreactive cell bodies and dystrophic dendrites in aging dogs resembles that in Alzheimer's disease

Elevated levels of the lysosomal enzyme cathepsin D are found in the early stages of Alzheimer's disease (AD) and co-occur with intraneuronal tangles. The present study tested whether increases in cathepsin D would emerge during aging in another mammalian species. Regional brain patterns of cathepsin D immunostaining were compared in dogs ages 0.35 to 16 years. Accumulations of immunopositive material were evident in neuronal cell bodies in many forebrain sites in middle-age to old dogs (>/=6 years). Three types could be distinguished: (1) dense aggregates with no particular position within the cell body; (2) crescent-shaped "caps" that occupied one pole of the cell body; and (3) very dense "spikes" that extended from the cell body for variable distances into the apical dendrite; these spikes were found in only a few areas, most notably the subiculum and layer V of neocortex. The spikes appeared between ages 2 and 5 years and increased steadily with age thereafter. Spikes were found in the subiculum in the aged human brain but only infrequently; they were, however, present in large numbers in AD brains. These results established that brain aging in dogs is (1) well advanced by middle age, (2) varies markedly across regions, and (3) in at least some of its aspects (dystrophic dendrites) is prominent in areas known to exhibit pathology early in the course of AD. Combined with previous results for rats, these findings indicated that changes in cathepsin D observed in AD, in particular in the temporal lobe, reflect a generalized mammalian pattern of brain aging.